General coding guidelines — Section I.B
Twenty rules that apply to every chapter and, unless stated otherwise, to every health care setting.
Section I.B holds twenty general coding guidelines that apply to every chapter of ICD-10-CM and, unless a guideline says otherwise, to every health care setting. They cover how to find a code, how much detail to report, signs and symptoms, multiple coding, sequelae, laterality, who may document what, complications of care and the correct use of unspecified codes.
The twenty general coding guidelines at a glance#
| # | Guideline | The rule |
|---|---|---|
| 1 | Locating a code | Index first, then verify in the Tabular List. The Index does not always give the full code; laterality and any 7th character can only be selected in the Tabular List. A dash (–) at the end of an Index entry means more characters are required — but even with no dash you must go to the Tabular List to check for a 7th character. |
| 2 | Level of detail | Report codes at their highest number of characters available and to the highest level of specificity documented. A 3-character code is used only if it is not further subdivided. |
| 3 | Code range | Use codes from A00.0 through T88.9, Z00–Z99.8 and U00–U85 to identify diagnoses, symptoms, conditions, problems, complaints or other reasons for the encounter. |
| 4 | Signs and symptoms | Acceptable for reporting when a related definitive diagnosis has not been established by the provider. Chapter 18 (R00.0–R99) holds many but not all symptom codes. |
| 5 | Integral to the disease process | NEVER Signs and symptoms routinely associated with a disease process are not assigned as additional codes, unless the classification instructs otherwise. |
| 6 | Not integral to the disease process | ALWAYS Additional signs and symptoms that are not routinely associated with the disease process should be coded when present. |
| 7 | Multiple coding for a single condition | Use additional code → add a secondary code, if known. Code first → the underlying condition is sequenced first, if known. Code, if applicable, any causal condition first → this code may be principal when the causal condition is unknown or not applicable. |
| 8 | Acute and chronic conditions | Same condition documented as both acute (subacute) and chronic, with separate Index subentries at the same indentation level → code both, acute first. |
| 9 | Combination code | One code classifying two diagnoses, or a diagnosis with an associated manifestation or complication. Assign the combination code alone when it fully identifies the conditions or the Index so directs. Add a secondary code only when the combination code lacks necessary specificity. |
| 10 | Sequela (late effects) | No time limit. Two codes, in this order: the residual condition first, the sequela code second. The code for the acute phase is never used with a late-effect code. |
| 11 | Impending or threatened condition | If it occurred → code as confirmed. If not → look for an Index subentry for impending or threatened, and the main terms Impending and Threatened. Subterm listed → assign it. Not listed → code the existing underlying condition(s) only. |
| 12 | Reporting the same code more than once | NEVER Each unique ICD-10-CM code may be reported only once per encounter — including for bilateral conditions with no laterality codes, and for two different conditions that classify to the same code. |
| 13 | Laterality | No bilateral code and the condition is bilateral → code both sides. Side not identified → unspecified side, which should rarely be used. See the table below for the two-encounter rule. |
| 14 | Documentation by clinicians other than the provider | Ten listed exceptions where another clinician's documentation may support code assignment. See the table below. |
| 15 | Syndromes | Follow Index guidance. Absent Index guidance, code the documented manifestations. Additional codes may be assigned for manifestations that are not an integral part of the disease process and have no unique code. |
| 16 | Documentation of complications of care | Based on the provider's documentation of the relationship between the condition and the care or procedure. Not everything that happens after care is a complication: there must be a cause-and-effect relationship and the condition must be clinically significant. The word “complication” need not appear. QUERY if the relationship is unclear. |
| 17 | Borderline diagnosis | Documented at discharge as “borderline” → code as confirmed, unless the classification has a specific entry (for example borderline diabetes). Borderline is not an uncertain diagnosis, so no distinction is made between inpatient and outpatient. |
| 18 | Sign, symptom and unspecified codes | These have acceptable, even necessary, uses. Code each encounter to the level of certainty known for that encounter. NEVER Select a specific code that the record does not support, and never order medically unnecessary testing to reach a more specific code. |
| 19 | Healthcare encounters in hurricane aftermath | External cause codes for the hurricane, sequenced after the injury code. Cataclysmic event codes outrank all other external cause codes except abuse and terrorism. See the table below. |
| 20 | Multiple sites coding | “Multiple” means two or more sites. Follow chapter-specific guidelines; absent those, code specified sites individually when documented, and use the “multiple sites” code only when the specific sites are not documented. |
Which codes may be assigned from another clinician's documentation?#
Ten items. Code assignment is normally based on the documentation of the patient's provider — the physician or other qualified health care practitioner legally accountable for establishing the diagnosis. Guideline I.B.14 lists ten exceptions where documentation by another clinician permitted to document in the official record may support code assignment.
| May be coded from another clinician's documentation | Typically documented by | Constraint |
|---|---|---|
| Body Mass Index (BMI) | Dietitian | Secondary diagnosis only |
| Depth of non-pressure chronic ulcers | Wound care nurse | — |
| Pressure ulcer stage | Nurse | — |
| Coma scale | EMT, emergency department staff | Secondary diagnosis only |
| NIH stroke scale (NIHSS) | Nurse, stroke coordinator | Secondary diagnosis only |
| Social determinants of health (Chapter 21) | Social worker, case manager, community health worker, nurse; or self-reported and signed off into the record | Secondary diagnosis only |
| Laterality | Any clinician documenting in the record | Query if documentation conflicts on the affected side |
| Blood alcohol level | Laboratory, nursing | Secondary diagnosis only |
| Underimmunization status | Nurse, immunisation record | Secondary diagnosis only |
| Firearm injury intent | Trauma team, emergency documentation | — |
How is laterality handled across two encounters?#
| Situation | Assign |
|---|---|
| Bilateral condition, no bilateral code exists | Separate codes for the left and the right side |
| Bilateral condition, each side treated at separate encounters — first encounter | The bilateral code — the condition still exists on both sides |
| Second encounter, first side treated and the condition no longer exists there | The appropriate unilateral code for the side where the condition still exists |
| Second encounter, but treatment of the first side did not completely resolve the condition | The bilateral code is still appropriate |
| Side not documented by the provider | Code assignment may be based on documentation from other clinicians |
| Conflicting documentation on the affected side | QUERY the patient's provider |
| Documentation insufficient and clarification impossible | The unspecified side code — which should rarely be used |
Sequela — the two-code rule#
| Point | Detail |
|---|---|
| Definition | The residual effect — the condition produced — after the acute phase of an illness or injury has terminated |
| Time limit | None. The residual may be apparent early, as in cerebral infarction, or months or years later, as with a previous injury |
| Examples in the guideline | Scar formation resulting from a burn; deviated septum due to a nasal fracture; infertility due to tubal occlusion from old tuberculosis |
| Sequence | The condition or nature of the sequela first; the sequela code second |
| The exception | Where the sequela code is followed by a manifestation code identified in the Tabular List and title, or the sequela code has been expanded at the 4th, 5th or 6th character to include the manifestation — then one code carries it |
| Absolute rule | NEVER The code for the acute phase of the illness or injury that led to the sequela is never used with a code for the late effect |
Unspecified codes are not a failure#
Guideline I.B.18 states that sign, symptom and unspecified codes have acceptable, even necessary, uses, and that each encounter should be coded to the level of certainty known for that encounter. A diagnosis of pneumonia without the specific organism is the guideline's own example of a legitimate unspecified code.
| Do | Do not |
|---|---|
| Report signs and symptoms in place of a definitive diagnosis when no definitive diagnosis was established by the end of the encounter | NEVER Select a specific code that the medical record documentation does not support |
| Report the appropriate unspecified code when sufficient clinical information is not known or available about the condition | NEVER Conduct medically unnecessary diagnostic testing in order to determine a more specific code |
| Review the entire record to determine the specific reason for the encounter and the conditions treated | NEVER Treat “unspecified” as automatically a coding error — sometimes it is the most accurate code available |
Complications of care — what makes it a complication?#
| Requirement | Detail |
|---|---|
| Provider documentation of the relationship | Code assignment rests on the provider's documentation of the relationship between the condition and the care or procedure, unless the classification instructs otherwise |
| Scope | The guideline extends to any complication of care, regardless of the chapter the code sits in |
| Cause and effect | There must be a cause-and-effect relationship between the care provided and the condition |
| Clinical significance | The documentation must support that the condition is clinically significant |
| The word itself | It is not necessary for the provider to explicitly document the term “complication”. If the condition alters the course of the surgery as documented in the operative report, a complication code is appropriate |
| When unclear | QUERY the provider for clarification of the relationship between the condition and the care or procedure |
Hurricane aftermath — guideline I.B.19#
| Element | Rule |
|---|---|
| External cause codes | Assigned to identify the cause of injuries incurred as a result of the hurricane, for each encounter for care and treatment. NEVER Never a principal or first-listed diagnosis — the injury code comes first |
| Not for medical conditions | Not assigned for encounters treating hurricane victims' medical conditions where no injury, adverse effect or poisoning is involved |
| Health care setting | Any location where medical care is provided by licensed health care professionals |
| Sequencing | Cataclysmic event codes take priority over all other external cause codes except child and adult abuse and terrorism |
| The hurricane code | X37.0- Hurricane, with the appropriate 7th character — also assigned for injury from flooding caused by a levee breaking related to the hurricane |
| Flood | X38.- Flood, for injury from flooding resulting directly from the storm |
| Collapse | NEVER Do not assign X36.0- when the collapse is due to the hurricane. X36.0- is limited to collapse of man-made structures due to earth surface movements |
| Not a direct result | For injuries not directly caused by the hurricane — an evacuee injured in a motor vehicle accident — code the cause of that injury but do not assign X37.0- |
| Unclear | If it is not clear whether the injury was a direct result of the hurricane, assume it was and assign X37.0- |
| Other applicable codes | X30- excessive natural heat, X31- excessive natural cold, X38- flood |
| Z codes | Z59.0- homelessness, Z59.1 inadequate housing, Z59.5 extreme poverty, Z75.1, Z75.3, Z75.4, Z76.2, Z99.12 — not an all-inclusive list |
Practice questions#
Q1A patient has bilateral cataracts and the right eye is operated on at this encounter. The left eye will be done in three weeks. There is a bilateral code available. What is reported for this encounter?
- AThe code for the right eye only, because that is the eye treated
- BThe bilateral code
- CSeparate codes for the right and left eye
- DThe unspecified eye code
Show answer & rationale
Correct answer: B. The bilateral code
Rationale. Guideline I.B.13 is explicit: when a patient has a bilateral condition and each side is treated during separate encounters, assign the bilateral code, including for the encounter to treat the first side, because the condition still exists on both sides. The unilateral code becomes appropriate only at the second encounter, once the condition no longer exists on the treated side.
Q2A dietitian documents a BMI of 43.2. The provider's documentation contains no diagnosis of obesity, overweight or any related condition. What may be coded?
- AThe BMI code from Z68 and a code for morbid obesity
- BThe BMI code from Z68 only, as a secondary diagnosis
- CNeither code
- DA code for morbid obesity only
Show answer & rationale
Correct answer: C. Neither code
Rationale. Two guidelines combine here. I.B.14 permits BMI to be coded from a clinician other than the provider, but requires the associated diagnosis to be documented by the patient's provider. Section I.C.21.c.3 adds that BMI codes should only be assigned when there is an associated, reportable diagnosis documented by the provider. With no such diagnosis there is nothing to attach the BMI code to, so neither code is reported. Querying the provider is the appropriate next step.
Q3A patient is treated for a scar contracture resulting from a burn sustained four years ago. How is this coded?
- AThe burn code with 7th character A, then the scar
- BThe scar, then the burn code with 7th character S
- CThe burn code with 7th character S only
- DThe scar only — the burn is too old to code
Show answer & rationale
Correct answer: B. The scar, then the burn code with 7th character S
Rationale. Guideline I.B.10 requires two codes with the nature of the sequela sequenced first and the sequela code second. Section I.C.19.a adds that the 7th character S is added only to the injury code, not to the sequela code, and that the specific type of sequela such as a scar is sequenced first. There is no time limit on when a sequela code may be used, and the code for the acute phase is never reported with the late effect.
Q4A discharge summary documents “borderline hypertension.” The patient was an outpatient. How is it coded?
- ADo not code it — borderline is an uncertain diagnosis and this is an outpatient encounter
- BCode it as confirmed hypertension unless the classification provides a specific borderline entry
- CCode elevated blood pressure reading instead in all cases
- DCode it as confirmed only for inpatients
Show answer & rationale
Correct answer: B. Code it as confirmed hypertension unless the classification provides a specific borderline entry
Rationale. Guideline I.B.17 states that a borderline diagnosis documented at the time of discharge is coded as confirmed, unless the classification provides a specific entry such as borderline diabetes, and that because borderline conditions are not uncertain diagnoses no distinction is made between inpatient and outpatient. The guideline also encourages a query where documentation about a borderline condition is unclear.
Q5Two entirely different conditions documented at one encounter both classify to the same ICD-10-CM code. How many times is that code reported?
- ATwice, once for each condition
- BOnce
- CTwice, with a modifier to distinguish them
- DIt depends on the setting
Show answer & rationale
Correct answer: B. Once
Rationale. Guideline I.B.12 states that each unique ICD-10-CM diagnosis code may be reported only once for an encounter, and applies that rule both to bilateral conditions where no distinct laterality codes exist and to two different conditions classified to the same ICD-10-CM diagnosis code.
Scenarios#
An office note documents both acute and chronic cholecystitis. The Alphabetic Index has separate subentries for acute and for chronic at the same indentation level under the main term.
Show coded answer & rationale
| Seq | Code | Description |
|---|---|---|
| 1 | 1 | the code for the acute form |
| 2 | 2 | the code for the chronic form |
Rationale. Guideline I.B.8 states that 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 code first. Note the two conditions in the rule: both must be documented, and separate subentries must exist at the same indentation level. Where a combination code exists for the acute-on-chronic condition, guideline I.B.9 governs instead and the combination code alone is assigned.
Guideline: Section I.B.8, I.B.9
A patient is admitted with acute appendicitis. The record documents right lower quadrant abdominal pain and also documents a new, unrelated productive cough that was evaluated with a chest radiograph.
Show coded answer & rationale
| Seq | Code | Description |
|---|---|---|
| 1 | 1 | acute appendicitis |
| 2 | 2 | the cough — reported because it is not integral to appendicitis and was separately evaluated |
Rationale. Guideline I.B.5 prohibits assigning signs and symptoms that are routinely associated with a disease process as additional codes — right lower quadrant pain is integral to appendicitis and is not coded separately. Guideline I.B.6 requires that additional signs and symptoms not routinely associated with the disease process be coded when present. The cough also satisfies Section III, because a diagnostic procedure was performed.
Guideline: Section I.B.5, I.B.6; Section III
A patient presents with severe substernal chest pain. The provider documents “impending myocardial infarction”. Serial troponins and electrocardiograms are negative; no infarction occurred. The Alphabetic Index has no subentry for impending under the relevant main terms, and the main terms Impending and Threatened do not lead to a usable entry for this condition.
Show coded answer & rationale
| Seq | Code | Description |
|---|---|---|
| 1 | 1 | the underlying condition(s) actually documented and treated — for example the unstable angina or the chest pain |
Rationale. Guideline I.B.11 sets out a four-step test for impending or threatened conditions. If it did occur, code it as confirmed. If it did not, check the Index for a subentry for impending or threatened and check the main terms Impending and Threatened. If the subterms are listed, assign the given code. If they are not listed, code the existing underlying condition(s) and not the condition described as impending or threatened.
Guideline: Section I.B.11
Primary sources#
- ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027CMS — the source document for every page on this site (effective 1 Oct 2026)
- NCHS ICD-10-CM files — Tabular List, Index, POA exempt listOfficial code files, addenda and the list of codes exempt from POA reporting
- ICD-10 Coordination and Maintenance CommitteeWhere code proposals are debated; agendas, summaries and meeting materials
- CMS ICD-10 homeCode sets, transition guidance and Medicare coding policy
- AHA Coding ClinicOfficial coding advice from the AHA Central Office — subscription required
- HHS OIG Work PlanActive audit topics — useful for prioritising internal coding audits
- MEDESUN Medical Coding AcademyTraining, credential preparation and audit services by the author