The first step to finding the most accurate code is to confirm that you are working with the correct version of the ICD-10-CM Official Guidelines for Coding and Reporting. The correct version may be the most recent update, or – in the context of retrospective coding– it may need to be a previous version that corresponds to the date of service, says Adrienne Commeree, MLS, RHIA, CPC, CPMA, CCS, CEMC, CPIP, professor at Tacoma Community College in Tacoma, Washington.
Either way, the CMS website includes PDFs of current guidelines, previous years’ guidelines, updates, and other helpful links. While it is highly recommended to reference the physical ICD-10-CM codebook, there are also convenient, free code look-up tools, such as ICD10Data.com.
Assessing Section I.B, General Coding Guidelines
Section I.B of the ICD-10-CM manual contains general guidelines that apply to the entire classification. These instructions, plus the conventions mentioned in Section I.A, take precedence over the coding guidelines in the Tabular and Alphabetic Index. Included are 19 headings. They range from the basic process of locating the proper code set to documenting complications of care.
This article will go through each section in detail.
Section I.B.1 of the 2025 ICD-10-CM guidelines
Section I.B.1 of the 2025 ICD-10-CM guidelines is as follows:
1. Locating a code in the ICD-10-CM
To select a code in the classification that corresponds to a diagnosis or reason for visit documented in a medical record, first locate the term in the Alphabetic Index, and then verify the code in the Tabular List. Read and be guided by instructional notations that appear in both the Alphabetic Index and the Tabular List.
It is essential to use both the Alphabetic Index and Tabular List when locating and assigning a code. The Alphabetic Index does not always provide the full code. Selection of the full code, including laterality and any applicable 7th character can only be done in the Tabular List. A dash (-) at the end of an Alphabetic Index entry indicates that additional characters are required. Even if a dash is not included at the Alphabetic Index entry, it is necessary to refer to the Tabular List to verify that no 7th character is required.
Key points:
- Start by checking for the main term in the Alphabetical Index
- Do NOT code solely from the Alphabetical Index, as it does not always contain full codes
- Verify codes in the Tabular List (be aware of laterality, 7th characters, notes, and exclusions)
This section explains how coders should approach locating a code. Commeree provides an example of finding a code for neuroblastoma.
“Let’s say that I want to find a code for a neuroblastoma of the nasal concha,” she says. “Neuroblastoma” is the main term. In the Alphabetic Index (located at the front of the coding book), finding the main term “neuroblastoma” would lead to the following entry:
Neuroblastoma
olfactory C30.0
specified site – see Neoplasm, malignant, by site
unspecified site C74.90
We have subterms in the first indentation of our main term, such as olfactory neuroblastoma, she explains, which is followed by C30.0. However, C30.0 is not necessarily the full code. We don’t know yet. We do not code directly from the alphabetic index.
Next, we have to verify this code in the Tabular List. Code C30.0 (malignant neoplasm of nasal cavity) is in Chapter 2 of the Tabular List for neoplasms. According to the list, this code includes malignant neoplasms in the cartilage of nose, nasal concha, internal nose, septum of nose, and vestibule of nose.
Code C30.0 also includes an Excludes1 note. Excludes1 notes indicate that the codes listed should never be reported with the main code under any circumstances. In this case, the Excludes1 note includes: malignant neoplasms of the nasal bone, nose not otherwise specified, olfactory bulb, posterior margin of nasal septum and choana, skin of nose, turbinates, and unspecified malignant neoplasm of skin of nose. In this case, the Excludes1 note does not interfere with the given details, so C30.0 is the most accurate code.
Section I.B.2 of the 2025 ICD-10-CM guidelines
Section I.B.2 is as follows:
2. Level of Detail in Coding
Diagnosis codes are to be used and reported at their highest number of characters available and to the highest level of specificity documented in the medical record.
ICD-10-CM diagnosis codes are composed of codes with 3, 4, 5, 6 or 7 characters. Codes with three characters are included in ICD-10-CM as the heading of a category of codes that may be further subdivided by the use of fourth and/or fifth characters and/or sixth characters, which provide greater detail.
A three-character code is to be used only if it is not further subdivided. A code is invalid if it has not been coded to the full number of characters required for that code, including the 7th character, if applicable.
Key points:
- Always code to the highest level of specificity that the documentation allows
- Codes that do not have the proper number of characters (up to seven) are invalid
Codes are arranged in categories and subcategories, with each subcategory adding a character (or more) to increase specificity. Some codes only consist of three characters, while others can have as many as seven.
“The code for hypertension, just hypertension in and of itself, is I10 (essential [primary] hypertension), and that’s the full code,” Commeree says.
However, there are other conditions in the hypertensive category that require more detail and more characters. For example, if a coder were to report I11.- (hypertensive heart disease) and just leave it at that, the code would be invalid. There are more characters needed in that code to indicate the type of hypertensive heart disease and whether it occurs with heart failure (I11.0) or without heart failure (I11.9).
Section I.B.3 of the 2025 ICD-10-CM guidelines
Section I.B.3 is as follows:
3. Code or codes from A00.0 through T88.9, Z00-Z99.8, U00-U85
The appropriate code or codes from A00.0 through T88.9, Z00-Z99.8, and U00-U85 must be used to identify diagnoses, symptoms, conditions, problems, complaints or other reason(s) for the encounter/visit.
Key point:
- Use as many codes as necessary from ranges A00.0-T88.9, Z00-Z99.8, and U00-U85 to identify why the patient went to go see the provider on that particular date of service
For example, a patient went to go see the provider due to a rash, Commeree says. The provider documents that the patient has “contact dermatitis due to cat dander.” So, maybe the patient visited friends with a cat and didn’t realize that they were allergic. The coder is going to look up “dermatitis” as the main term. “Contact” is an adjective– you’re not going to find the proper code under that term, and the same goes for “cat.” After finding “dermatitis,” you’d then follow the instructional note “see Dermatitis, contact, allergic.” This brings you to “contact,” from which you can find “allergic,” then “due to,” then “dander (cat) (dog) L23.81.”
Remember, you have to verify codes in the Tabular List. You’re going to take a look at Chapter 12, where the L codes are listed. It’s going to be under category 23, allergic contact dermatitis, under which there are subcategories, including L23.8- (allergic contact dermatitis due to other agents). In this case, the other agent is an animal, which leads to code L23.81 (allergic contact dermatitis due to animal [cat] [dog] dander). That code represents the reason why the patient went to see the provider that day.
Section I.B.4 of the 2025 ICD-10-CM guidelines
Section I.B.4 is as follows:
4. Signs and symptoms
Codes that describe symptoms and signs, as opposed to diagnoses, are acceptable for reporting purposes when a related definitive diagnosis has not been established (confirmed) by the provider. Chapter 18 of ICD-10-CM, Symptoms, Signs, and Abnormal Clinical and Laboratory Findings, Not Elsewhere Classified (codes R00.0 – R99) contains many, but not all, codes for symptoms.
See Section I.B.18. Use of Signs/Symptom/Unspecified Codes
Key point:
- Symptom codes (codes in range R00.0-R99) can be used until a definitive diagnosis is obtained
Commeree offers an example. A patient presents with an acute cough of uncertain cause. The provider instructs the patient to come back in a day or two to run some tests for an upper respiratory infection (URI). For this encounter, the provider has not established a definitive diagnosis, so the coder would report a code from range R00.0-R99 as the first-listed diagnosis code. Use code R05.1 (acute cough).
Section I.B.5 of the 2025 ICD-10-CM guidelines
Section I.B.5 is as follows:
5. Conditions that are an integral part of a disease process
Signs and symptoms that are associated routinely with a disease process should not be assigned as additional codes, unless otherwise instructed by the classification.
Key point:
- Do not report signs and symptoms that are routinely associated with a disease, unless otherwise instructed.
If a definitive diagnosis is established, the coder should not report signs and symptoms that are commonly and routinely associated with the disease. For example, a provider has established that a patient has a URI. He also documents that the patient has symptoms of acute cough and runny nose. These two symptoms are known symptoms of URIs, so it would be redundant for the coder to report them along with the diagnosis code.
Knowledge of the disease process is very important to discern which signs and symptoms “belong” to the patient’s condition.
Section I.B.6 of the 2025 ICD-10-CM guidelinesSection
I.B.6 is as follows:
6. Conditions that are not an integral part of a disease process
Additional signs and symptoms that may not be associated routinely with a disease process should be coded when present.
Key point:
- Signs and symptoms that are not routinely associated with a disease should be reported
For example, the patient presents with an acute cough and leg pain, Commeree says. Tests indicate that the patient has COVID-19. Leg pain is not a symptom associated with the disease process of COVID-19, so the symptom of leg pain would be reported separately. An acute cough, on the other hand, is an associated symptom, so it would not be reported. This could also apply if the patient was being treated for osteomyelitis (a disease associated with leg pain) and also had a cough– the cough can be coded.
Section I.B.7 of the 2025 ICD-10-CM guidelines
Section I.B.7 is as follows:
7. Multiple coding for a single condition
In addition to the etiology/manifestation convention that requires two codes to fully describe a single condition that affects multiple body systems, there are other single conditions that also require more than one code. “Use additional code” notes are found in the Tabular List at codes that are not part of an etiology/manifestation pair where a secondary code is useful to fully describe a condition. The sequencing rule is the same as the etiology/manifestation pair, “use additional code” indicates that a secondary code should be added, if known.
For example, for bacterial infections that are not included in chapter 1, a secondary code from category B95, Streptococcus, Staphylococcus, and Enterococcus, as the cause of diseases classified elsewhere, or B96, Other bacterial agents as the cause of diseases classified elsewhere, may be required to identify the bacterial organism causing the infection. A “use additional code” note will normally be found at the infectious disease code, indicating a need for the organism code to be added as a secondary code.
“Code first” notes are also under certain codes that are not specifically manifestation codes but may be due to an underlying cause. When there is a “code first” note and an underlying condition is present, the underlying condition should be sequenced first, if known.
“Code, if applicable, any causal condition first” notes indicate that this code may be assigned as a principal diagnosis when the causal condition is unknown or not applicable. If a causal condition is known, then the code for that condition should be sequenced as the principal or first-listed diagnosis.
Multiple codes may be needed for sequela, complication codes and obstetric codes to more fully describe a condition. See the specific guidelines for these conditions for further instruction.
Key points:
- Etiology/manifestation conventions require two codes:
- A code for the underlying cause, such as bacteria, virus, or fungi
- A code for the manifestation
- Watch out for (and follow) coding instructions in the Tabular List, such as “code first,” “use additional code” and “code, if applicable, any causal condition first”
“Code first” is a sequencing mandate, but there may be instances where a patient may have one condition in and of itself and they may not necessarily have that other underlying condition, Commeree points out.
She also offers an example. Code N13.6 (pyonephrosis) includes the instructions in the Tabular List for coders to “use additional code” to identify the infectious agent and includes the code range B95-B97. That gives you a list of all different types of codes for staphylococcus, streptococcus, E. coli, and other infections. So, you would report the code for the infectious agent after N13.6.
Section I.B.8 of the 2025 ICD-10-CM guidelines
Section I.B.8 is as follows:
8. Acute and Chronic Conditions
If the same condition is described as both acute (subacute) and chronic, and separate subentries exist in the Alphabetic Index at the same indentation level, code both and sequence the acute (subacute) code first.
Key point:
- If a condition is both acute and chronic, and both subentries are on the same indentation level in the Alphabetic Index, report the acute code first, then the chronic code.
Chronic conditions are “conditions that last one year or more and require ongoing medical attention or limit activities of daily living or both,” according to the Centers for Disease Control and Prevention (CDC). They require treatment on an ongoing basis. They can be reported as many times as that patient receives treatment and care for that condition. Examples include hypertension, chronic obstructive pulmonary disorder (COPD), and diabetes.
In coding, the span of time it takes for a condition to be considered chronic varies from illness to illness, and some do not even have a set time requirement. On the subject of chronic pain, the 2025 ICD-10-CM guidelines state, “There is no time frame defining when pain becomes chronic pain.” Therefore, coders must rely on provider discretion as to whether a condition is considered acute, chronic, or acute on chronic.
Some patients have both acute and chronic versions of the same condition. For example, a patient presents with both acute bronchitis and chronic bronchitis. You would look up the main term “bronchitis” — not “acute” or “chronic,” because those are adjectives– “bronchitis” in the Alphabetic Index, and you would find:
Bronchitis, (diffuse) (fibrous) (hypostatic) (infective) (membranous) J40
…acute or subacute (with bronchospasm or obstruction) J20.9
…chronic J42
Both “acute” and “chronic” are on the same indentation level, so, after verifying the codes in the Tabular List, you would report both conditions, with J20.9 (acute bronchitis, unspecified) being first, followed by J42 (unspecified chronic bronchitis).
Section I.B.9 of the 2025 ICD-10-CM guidelines
Section I.B.9 is as follows:
9. Combination Code
A combination code is a single code used to classify:
- Two diagnoses, or
- A diagnosis with an associated secondary process (manifestation)
- A diagnosis with an associated complication
Combination codes are identified by referring to subterm entries in the Alphabetic Index and by reading the inclusion and exclusion notes in the Tabular List.
Assign only the combination code when that code fully identifies the diagnostic conditions involved or when the Alphabetic Index so directs. Multiple coding should not be used when the classification provides a combination code that clearly identifies all of the elements documented in the diagnosis. When the combination code lacks necessary specificity in describing the manifestation or complication, an additional code should be used as a secondary code.
Key points:
- A combination code can classify two diagnoses, a diagnosis and a manifestation, or a diagnosis with a complication
- Ensure all parts of a combination code’s description is fulfilled before reporting it
The example that Commeree presents for the appropriate use of a combination code is for a diagnosis with an associated complication. A patient with Crohn’s disease of their large and small intestine presents with a gastrointestinal issue that turns out to be an intestinal blockage. The patient’s Crohn’s disease, a chronic condition, was complicated by the intestinal obstruction.
ICD-10-CM code K50.812 (Crohn’s disease of both small and large intestines with intestinal obstruction) would be the most appropriate code in this case. There’s a lot of information in that one combination code: Crohn’s disease, the fact that it’s affecting both the small and the large intestine, and an obstruction. Code K0.812 accurately describes all of that.
Something to keep in mind is that combination codes may have instructional notes in the Tabular List. Code K50.812, for example, instructs coders to use an additional code to identify manifestations, such as pyoderma gangrenosum (L88).
Section I.B.10 of the 2025 ICD-10-CM guidelines
Section I.B.10 is as follows:
10. Sequela (Late Effects)
A sequela is the residual effect (condition produced) after the acute phase of an illness or injury has terminated. There is no time limit on when a sequela code can be used.
The residual may be apparent early, such as in cerebral infarction, or it may occur months or years later, such as that due to a previous injury. Examples of sequela include: scar formation resulting from a burn, deviated septum due to a nasal fracture, and infertility due to tubal occlusion from old tuberculosis. Coding of sequela generally requires two codes sequenced in the following order: the condition or nature of the sequela is sequenced first. The sequela code is sequenced second.
An exception to the above guidelines is those instances where the code for the sequela is followed by a manifestation code identified in the Tabular List and title, or the sequela code has been expanded (at the fourth, fifth or sixth character levels) to include the manifestation(s). The code for the acute phase of an illness or injury that led to the sequela is never used with a code for the late effect.
See Section I.C.9. Sequelae of cerebrovascular disease
See Section I.C.15. Sequelae of complication of pregnancy, childbirth and the puerperium
See Section I.C.19. Application of 7th characters for Chapter 19
Key point:
- There is no time limitation for when the sequela codes can be used
Sequela codes give additional context to current conditions and show a connection between a previous known event or diagnosis and the current one. Whether the original event happened months ago or years ago, it should be reported, says Commeree.
For example, a patient presents with arthritis in his left elbow. After getting his history, the provider finds that he had suffered from a simple displaced humeral supracondylar fracture without intercondylar fracture in the same elbow from a fall as a child. The coder would report both M12.522 (traumatic arthropathy, left elbow) to represent the present arthritis and S42.412S (displaced simply supracondylar fracture without intercondylar fracture of left humerus, sequela).
Note that the sequela code has seven characters and ends with the character “S.” This letter will change depending on the encounter during which the provider makes the diagnosis of the patient, such as an initial encounter, a subsequent encounter, or sequela.
Section I.B.11 of the 2025 ICD-10-CM guidelines
Section I.B.11 is as follows:
11. Impending or Threatened Condition
Code any condition described at the time of discharge as “impending” or “threatened” as follows:
If it did occur, code as confirmed diagnosis.
If it did not occur, reference the Alphabetic Index to determine if the condition has a subentry term for “impending” or “threatened” and also reference main term entries for “Impending” and for “Threatened.”
If the subterms are listed, assign the given code.
If the subterms are not listed, code the existing underlying condition(s) and not the condition described as impending or threatened.
Key points:
- Impeding or threatened condition codes are for conditions that have NOT occurred by the time of discharge or time of patient leaving the visit.
For example, a pregnant patient presents to the emergency department complaining of irregular contractions. She’s in the 32nd week and was given a treatment to stop the contractions and was put on bedrest. The documented diagnosis was “threatened labor.”
So if you look at the main term “threatened” in the alphabetic index, you are going to find a subentry for “labor without delivery.” This is going to be in, this is the default code, O47.9. If it’s before 37 weeks, O47.0 there indicating that you need to have some additional characters.
O47.03, False labor before 37 completed weeks of gestation, third trimester
Section I.B.7 of the 2025 ICD-10-CM guidelines
Section I.B.12 is as follows:
12. Reporting Same Diagnosis Code More than Once
Each unique ICD-10-CM diagnosis code may be reported only once for an encounter. This applies to bilateral conditions when there are no distinct codes identifying laterality or two different conditions classified to the same ICD-10-CM diagnosis code.
Key point:
- Only report each ICD-10-CM code once per date of service
This guideline necessitates extra research in both the Alphabetic Index and Tabular List to discern whether the bilateral condition code is the only code for the condition.
Section I.B.13 of the 2025 ICD-10-CM guidelines
Section I.B.13 is as follows:
13. Laterality
Some ICD-10-CM codes indicate laterality, specifying whether the condition occurs on the left, right or is bilateral. If no bilateral code is provided and the condition is bilateral, assign separate codes for both the left and right side. If the side is not identified in the medical record, assign the code for the unspecified side.
When a patient has a bilateral condition and each side is treated during separate encounters, assign the “bilateral” code (as the condition still exists on both sides), including for the encounter to treat the first side. For the second encounter for treatment after one side has previously been treated and the condition no longer exists on that side, assign the appropriate unilateral code for the side where the condition still exists (e.g., cataract surgery performed on each eye in separate encounters). The bilateral code would not be assigned for the subsequent encounter, as the patient no longer has the condition in the previously-treated site. If the treatment on the first side did not completely resolve the condition, then the bilateral code would still be appropriate.
When laterality is not documented by the patient’s provider, code assignment for the affected side may be based on medical record documentation from other clinicians. If there is conflicting medical record documentation regarding the affected side, the patient’s provider should be queried for clarification. Codes for “unspecified” side should rarely be used, such as when the documentation in the record is insufficient to determine the affected side and it is not possible to obtain clarification.
Key points:
- When able, include laterality in the chosen code
- Always report codes to the highest level of specificity, especially with fractures
- Unspecified codes should only be used as last resort
Specificity of conditions is very important for coders to capture, as the patient may go to different specialists for the same condition, but the codes must accurately and consistently reflect the condition and its location. In coding, the fifth and sixth characters identify laterality.
For example, a patient presents after experiencing a motorcycle accident in which they breaks both of their arms. They sustained Smith’s fractures of the right radius and a closed Barton’s fracture of the left radius. You would not indicate that the patient has bilateral fractures. You’re not going to see bilateral codes in injuries. The providers would want more specificity and would want more information on which type of fracture occurred where. Therefore, the coder would report S52.541A (Smith’s fracture of right radius, initial encounter for closed fracture) and S52.562A (Barton’s fracture of left radius, initial encounter for closed fracture) to represent the respective injuries.
Section I.B.14 of the 2025 ICD-10-CM guidelines
Section I.B.14 is as follows:
14. Documentation by Clinicians Other than the Patient’s Provider
Code assignment is based on the documentation by the patient’s provider (i.e., physician or other qualified healthcare practitioner legally accountable for establishing the patient’s diagnosis). There are a few exceptions when code assignment may be based on medical record documentation from clinicians who are not the patient’s provider (i.e., physician or other qualified healthcare practitioner legally accountable for establishing the patient’s diagnosis). In this context, “clinicians” other than the patient’s provider refer to healthcare professionals permitted, based on regulatory or accreditation requirements or internal hospital policies, to document in a patient’s official medical record.
These exceptions include codes for:
- Body Mass Index (BMI)
- Depth of non-pressure chronic ulcers
- Pressure ulcer stage
- Coma scale
- NIH stroke scale (NIHSS)
- Social determinants of health (SDOH) classified to Chapter 21
- Laterality
- Blood alcohol level
- Underimmunization status
This information is typically, or may be, documented by other clinicians involved in the care of the patient (e.g., a dietitian often documents the BMI, a nurse often documents the pressure ulcer stages, and an emergency medical technician often documents the coma scale). However, the associated diagnosis (such as overweight, obesity, acute stroke, pressure ulcer, or a condition classifiable to category F10, Alcohol related disorders) must be documented by the patient’s provider. If there is conflicting medical record documentation, either from the same clinician or different clinicians, the patient’s provider should be queried for clarification.
The BMI, coma scale, NIHSS, blood alcohol level codes, codes for social determinants of health and underimmunization status should only be reported as secondary diagnoses.
See Section I.C.21.c.17. for additional information regarding coding social determinants of health.
Key points:
- Coders can use documentation provided by clinicians other than the patient’s provider to gain more information to report certain codes with the highest level of specificity
- The associated diagnosis must be documented by the patient’s provider
For example, if the patient comes in acutely intoxicated and there is documentation about their blood alcohol level, perhaps in the ambulance notes or nursing notes, the coder may use those notes to report the most appropriate code. But, the diagnosis of intoxication has to have been documented by the provider.
Section I.B.15 of the 2025 ICD-10-CM guidelines
Section I.B.15 is as follows:
15. Syndromes
Follow the Alphabetic Index guidance when coding syndromes. In the absence of Alphabetic Index guidance, assign codes for the documented manifestations of the syndrome. Additional codes for manifestations that are not an integral part of the disease process may also be assigned when the condition does not have a unique code.
Key points:
- When coding syndromes, use the Alphabetic Index for guidance
- If no guidance is available, or if there is no unique code, report the documented manifestations.
“A syndrome is a recognizable complex of symptoms and physical findings which indicate a specific condition for which a direct cause is not necessarily understood,” according to the American Medical Informatics Association.
One example is Sjögren’s syndrome. This syndrome describes an autoimmune disease that affects the entire body by compromising cells that produce tears, saliva, and mucus. It affects women more often than men and can be progressive or stay consistent throughout the patient’s life. ICD-10-CM code M35.07 (Sjögren’s syndrome with central nervous system involvement) describes the syndrome and includes instructions to “use additional code” to capture associated manifestations.
Section I.B.16 of the 2025 ICD-10-CM guidelines
Section I.B.16 is as follows:
16. Documentation of Complications of Care
Code assignment is based on the provider’s documentation of the relationship between the condition and the care or procedure, unless otherwise instructed by the classification. The guideline extends to any complications of care, regardless of the chapter the code is located in. It is important to note that not all conditions that occur during or following medical care or surgery are classified as complications. There must be a cause-and-effect relationship between the care provided and the condition, and the documentation must support that the condition is clinically significant. It is not necessary for the provider to explicitly document the term “complication.” For example, if the condition alters the course of the surgery as documented in the operative report, then it would be appropriate to report a complication code. Query the provider for clarification if the documentation is not clear as to the relationship between the condition and the care or procedure.
Key points:
- Complications, by their nature, will go across many classifications and areas, i.e. circulatory system, respiratory, digestive, and conditions, such as diabetes.
- Not all conditions that occur following a procedure are complications, so care must be used in analyzing documentation
Example:
Coding for complications of care can get really difficult because there are specific codes that identify complications and can affect providers’ quality ratings, so this is definitely something that you need to watch out for, says Commeree.
Coders should remember that not all conditions that occur following a procedure are classified as complications. Commeree gives the following example: When a patient has their joint replaced, like a hip replacement, there’s going to be a lot of bleeding. That is just par for the course when you’re getting the joint replacement. So, a significant amount of blood loss is not necessarily considered acute postoperative hemorrhaging. However, if the provider documents a cause-and-effect relationship between that joint replacement and perhaps a significant blood loss where the patient becomes anemic, that could be considered a complication. Documentation has to support that the condition of anemia is clinically significant.
Section I.B.17 of the 2025 ICD-10-CM guidelines
Section I.B.17 is as follows:
17. Borderline Diagnosis
If the provider documents a “borderline” diagnosis at the time of discharge, the diagnosis is coded as confirmed, unless the classification provides a specific entry (e.g., borderline diabetes). If a borderline condition has a specific index entry in ICD-10-CM, it should be coded as such. Since borderline conditions are not uncertain diagnoses, no distinction is made between the care setting (inpatient versus outpatient). Whenever the documentation is unclear regarding a borderline condition, coders are encouraged to query for clarification.
Key points:
- Report a “borderline” diagnosis at time of discharge as confirmed, unless there is a separate specific entry.
The Alphabetic Index includes the following options under the main term “borderline”:
Borderline
diabetes mellitus R73.03
hypertension R03.0
osteopenia M85.8-
pelvis, with obstruction during labor O65.1
personality F60.3
For example, a patient’s test for hypertension is just under the numeric limit for the condition. In this case, the coder would report “borderline” code R03.0 (elevated blood-pressure reading, without diagnosis of hypertension).
Section I.B.18 of the 2025 ICD-10-CM guidelines
Section I.B.18 is as follows:
18. Use of Sign/Symptom/Unspecified Codes 1
Sign/symptom and “unspecified” codes have acceptable, even necessary, uses. While specific diagnosis codes should be reported when they are supported by the available medical record documentation and clinical knowledge of the patient’s health condition, there are instances when signs/symptoms or unspecified codes are the best choices for accurately reflecting the healthcare encounter. Each healthcare encounter should be coded to the level of certainty known for that encounter.
As stated in the introductory section of these official coding guidelines, a joint effort between the healthcare provider and the coder is essential to achieve complete and accurate documentation, code assignment, and reporting of diagnoses and procedures. The importance of consistent, complete documentation in the medical record cannot be overemphasized. Without such documentation, accurate coding cannot be achieved. The entire record should be reviewed to determine the specific reason for the encounter and the conditions treated.
If a definitive diagnosis has not been established by the end of the encounter, it is appropriate to report codes for sign(s) and/or symptom(s) in lieu of a definitive diagnosis. When sufficient clinical information isn’t known or available about a particular health condition to assign a more specific code, it is acceptable to report the appropriate “unspecified” code (e.g., a diagnosis of pneumonia has been determined, but not the specific type). Unspecified codes should be reported when they are the codes that most accurately reflect what is known about the patient’s condition at the time of that particular encounter. It would be inappropriate to select a specific code that is not supported by the medical record documentation or conduct medically unnecessary diagnostic testing in order to determine a more specific code.
Key points:
- Unspecified codes should be used as a last resort, but there are still instances in which they are the most applicable coding option
- If a definitive diagnosis has not been established by the end of the encounter, the coder may report signs and symptoms
Although a patient’s care relies on facts and certainty, there are some occasions in which the diagnosis is uncertain. In these cases, the coder could report signs and symptoms in lieu of the definitive diagnosis.
However, the coding protocol differs depending on whether you are reporting for an inpatient or outpatient facility, Commeree points out. If you are doing outpatient coding, coders are to only report signs, symptoms, or diagnosis that are definitive. If documentation includes verbiage such as “probable,” “suspected,” “compatible with working diagnosis,” or anything that indicates uncertainty, the outpatient coder is not to report it. This goes against the directions given to inpatient coders, who are instructed to “code the condition as if it existed or was established,” according to Section II.H of the 2025 ICD-10-CM guidelines.
Section I.B.19 of the 2025 ICD-10-CM guidelines
Section I.B.19 is as follows:
19. Coding for Healthcare Encounters in Hurricane Aftermath
a. Use of External Cause of Morbidity Codes
An external cause of morbidity code should be assigned to identify the cause of the injury(ies) incurred as a result of the hurricane. The use of external cause of morbidity codes is supplemental to the application of ICD-10-CM codes. External cause of morbidity codes are never to be recorded as a principal diagnosis (first- listed in non-inpatient settings). The appropriate injury code should be sequenced before any external cause codes. The external cause of morbidity codes capture how the injury or health condition happened (cause), the intent (unintentional or accidental; or intentional, such as suicide or assault), the place where the event occurred, the activity of the patient at the time of the event, and the person’s status (e.g., civilian, military). They should not be assigned for encounters to treat hurricane victims’ medical conditions when no injury, adverse effect or poisoning is involved. External cause of morbidity codes should be assigned for each encounter for care and treatment of the injury. External cause of morbidity codes may be assigned in all health care settings. For the purpose of capturing complete and accurate ICD-10-CM data in the aftermath of the hurricane, a healthcare setting should be considered as any location where medical care is provided by licensed healthcare professionals.
b. Sequencing of External Causes of Morbidity Codes
Codes for cataclysmic events, such as a hurricane, take priority over all other external cause codes except child and adult abuse and terrorism and should be sequenced before other external cause of injury codes. Assign as many external cause of morbidity codes as necessary to fully explain each cause. For example, if an injury occurs as a result of a building collapse during the hurricane, external cause codes for both the hurricane and the building collapse should be assigned, with the external causes code for hurricane being sequenced as the first external cause code. For injuries incurred as a direct result of the hurricane, assign the appropriate code(s) for the injuries, followed by the code X37.0-, Hurricane (with the appropriate 7th character), and any other applicable external cause of injury codes. Code X37.0- also should be assigned when an injury is incurred as a result of flooding caused by a levee breaking related to the hurricane. Code X38.-, Flood (with the appropriate 7th character), should be assigned when an injury is from flooding resulting directly from the storm. Code X36.0.-, Collapse of dam or man- made structure, should not be assigned when the cause of the collapse is due to the hurricane. Use of code X36.0- is limited to collapses of man-made structures due to earth surface movements, not due to storm surges directly from a hurricane.
c. Other External Causes of Morbidity Code Issues
For injuries that are not a direct result of the hurricane, such as an evacuee that has incurred an injury as a result of a motor vehicle accident, assign the appropriate external cause of morbidity code(s) to describe the cause of the injury, but do not assign code X37.0-, Hurricane. If it is not clear whether the injury was a direct result of the hurricane, assume the injury is due to the hurricane and assign code X37.0-, Hurricane, as well as any other applicable external cause of morbidity codes. In addition to code X37.0-, Hurricane, other possible applicable external cause of morbidity codes include:
X30-, Exposure to excessive natural heat
X31-, Exposure to excessive natural cold
X38-, Flood
d. Use of Z codes
Z codes (other reasons for healthcare encounters) may be assigned as appropriate to further explain the reasons for presenting for healthcare services, including transfers between healthcare facilities, or provide additional information relevant to a patient encounter. The ICD-10-CM Official Guidelines for Coding and Reporting identify which codes may be assigned as principal or first-listed diagnosis only, secondary diagnosis only, or principal/first-listed or secondary (depending on the circumstances). Possible applicable Z codes include:
Z59.0-, Homelessness
Z59.1, Inadequate housing
Z59.5, Extreme poverty
Z75.1, Person awaiting admission to adequate facility elsewhere
Z75.3, Unavailability and inaccessibility of health-care facilities Z75.4, Unavailability and inaccessibility of other helping agencies
Z76.2, Encounter for health supervision and care of other healthy infant and child
Z99.12, Encounter for respirator [ventilator] dependence during power failure
The external cause of morbidity codes and the Z codes listed above are not an all-inclusive list. Other codes may be applicable to the encounter based upon the documentation. Assign as many codes as necessary to fully explain each healthcare encounter. Since patient history information may be very limited, use any available documentation to assign the appropriate external cause of morbidity and Z codes
Key points:
- External cause of morbidity codes give supplemental information about injuries and conditions (i.e., cause, intent, place, activity, status)
- External cause codes should never be reported as the primary diagnosis
- Z codes offer supplemental information, too, but certain ones can be reported as the primary diagnosis
Documenting details of a patient’s injury or condition is often given the most attention in provider notes (and rightly so), but capturing the events that led to the injury or condition is also very important. This section and its subheadings offer direction on how to implement external cause of morbidity codes, which are located in categories V00 (pedestrian conveyance accident) through Y99 (external cause status), specifically for hurricanes. It also includes Z codes from Chapter 21: Factors Influencing Health Status and Contact with Health Services, which also give more information to claims, such as encounters, and socioeconomic or psychosocial circumstances that impact the patient’s healthcare.
References
1 Just Coding article – Uncertain diagnosis? Outpatient coding is different by Dr. Shelley Safian