Introduction

The International Classification of Diseases, 10th Revision, Clinical Modification (ICD-10-CM) is a morbidity classification published by the Centers for Medicare and Medicaid Services (CMS) and the National Center for Health Statistics (NCHS), two departments within the U.S. Department of Health and Human Services (DHHS).

The ICD-10-CM is based on the ICD-10, the classification of disease published by the World Health Organization (WHO).

ICD-10-CM is used for classifying diagnoses and reason for visits in all health care settings in the United States. It contains more than 74,000 codes compared to approximately 14,000 codes in its predecessor, ICD-9-CM.

This product contains 2027 ICD-10-CM codes, which are to be used for services provided in the United States from October 1, 2026 through September 30, 2027.

Structure and Format

ICD-10-CM codes have between 3 and 7 characters and have the following characteristics:

• Character types:
  • 1st character: always alpha (all letters except "U")
  • 2nd character: numeric (0-9)
  • 3rd–7th character: alpha or numeric
• Decimal: placed after the 3rd character
• Structure
  
  • Chapter: ICD-10-CM is organized into 22 chapters based on anatomic or etiologic groupings.
    Example: "Chapter 1 - Certain infectious and parasitic diseases (A00-B99)"
  • Section: chapters are divided into Sections corresponding to logical grouping of diseases.
    Example: "Intestinal infectious diseases (A00-A09)"
  • Category: the first 3 characters of an ICD-10-CM code designate the diagnosis category.
    Example: "A00 - Cholera"
  • Etiology, Anatomic Site, Severity: the 4th–6th character correspond to etiology, anatomic site, severity, or other clinical details.
    Example: "A00.0 - Cholera due to Vibrio cholerae 01, biovar cholerae"
  • Extension: a 7th character is required in certain sections to encode characteristics of the patient encounter. If there are fewer than 6 characters in the code the placeholder character "X" is used to ensure that the seventh character is always in the seventh position.
    Example: "S03.4xxA - Sprain of jaw, initial encounter"

Common Abbreviations

• NEC: "Not elsewhere classified" - used when there is no specific code available to represent the condition.
  Example: "A41.89 - Other specified sepsis" is used when sepsis is caused by an organism not specifically listed in ICD-10-CM as a cause of sepsis
• NOS: "Not otherwise specified" - equivalent to the word "unspecified" and indicates that the condition or documentation does not provide enough information to assign a more specific code.
  Example: "597.81 - Urethral syndrome NOS"

The 2027 ICD-10-CM update, released by the CDC and effective October 1, 2026, introduces 190 new diagnosis codes, revises 4 codes, and removes 30 codes, bringing the total to 74,879 codes. Updates to the guidelines include the expansion of Chapter 17 to cover genetic disorders, new instructional notes for diethylstilbestrol (DES) exposure, and clarifications for hypertensive heart disease and present on admission reporting.

2027 ICD-10-CM Coding Highlights

Finding the Best-Fit Code

The ICD-10-CM Alphabetical Index contains terms and their corresponding code, organized in these areas:

• Diseases and Injuries
• External Causes of Injuries
• Neoplasms
• Drugs and Chemicals

To find the best-fit code:

1. Select one of the indexes above
2. Enter your term or phrase in the "Jump To" box (mobile) or browse the A-Z list (web)
3. Select the most appropriate index terms provided, until reaching a code

Confirming the Code

To confirm the code:

1. Review and investigate any Instructional Notations associated with the code
2. Review the Code Tree (see below) to confirm that the most specific code is being assigned

Code Tree

This product provides a complete tree (hierarchy) for each ICD-10-CM code.

Each tree may contain the following levels:

Categories and codes are denoted in color as either Non-Billable or Billable:

Code Key

• Reimbursement
  • [Billable] = an ICD-10-CM code that can be used to indicate a diagnosis for reimbursement purposes
  • [Non-Billable] = an ICD-10-CM diagnosis code that is not billable

• Present on Admission (POA)
  
  • [POA Exempt] = an ICD-10-CM code that is exempt from POA reporting
  • A condition is POA if it is present at the time of inpatient admission. Conditions that develop during an outpatient encounter, including in the emergency department or outpatient surgery, are considered POA.

• ICD Structure
  • [Chapter] = one of 21 ICD-10-CM chapters that organizes codes based on anatomic or etiologic groups
  • [Section] = a logical grouping of disease codes within a chapter

Introduction

Accompanying many ICD-10-CM codes are instructional notations. Note types are described below.

Includes

• "Includes" notes define, or give examples of, the code or category.

Excludes

Code First/Use Additional Code

• Certain conditions have both an underlying etiology and multiple body system manifestations.
  • The ICD-10-CM coding convention requires the underlying condition be sequenced first followed by the manifestation.
  • Wherever such a combination exists there is a "Use Additional Code" note at the etiology code, and a "Code First" note at the manifestation code.
  • These instructional notes indicate the proper sequencing order of the codes, etiology followed by manifestation.
• In most cases manifestation codes will have in the code title, "in diseases classified elsewhere."
  
  • These codes are never permitted to be used as first listed or principal diagnosis codes.
  • They must be used in conjunction with an underlying condition code and they must be listed following the underlying condition.

Code Also

• A "Code Also" note instructs that two codes may be required to fully describe a condition but the sequencing of the two codes is discretionary, depending on the severity of the conditions and the reason for the encounter.

Introduction

The Centers for Medicare and Medicaid Services (CMS) has published the ICD-10-CM Official Guidelines for Coding and Reporting 2027 [PDF - 121 pages].

Reproduced below are the General Coding Guidelines (Section I. B.).

It is recommended that these guidelines be used as a companion to this product to assure accurate coding.

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.

Level of Detail in Coding

Diagnosis codes are to be used and reported at their highest number of characters available.

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.

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.

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.

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.

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.

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.

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.

“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.

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.

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.

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 are 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.

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.

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.

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.

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.

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.

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.

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.

Use of Sign/Symptom/Unspecified Codes

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.

Coding for Healthcare Encounters in Hurricane Aftermath

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.

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.

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

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 maybe 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.

Chapter-Specific Coding Guidelines

In addition to general coding guidelines, there are guidelines for specific diagnoses and/or conditions in the classification (see ICD-10-CM Official Guidelines for Coding and Reporting 2027 [PDF]).

Key changes in 2027:

• Chapter 17: retitled Congenital malformations, deformations, chromosomal abnormalities, and genetic disorders (Q00-QA1); the guidelines now treat a genetic disorder the same as a malformation, deformation, or chromosomal abnormality.
• Hypertension: "Code also any identified hypertensive disease" revised to (I10-I15, I1A); hypertensive heart disease clarified to "one or more heart conditions."
• DES exposure: new notes distinguishing Z84.A (a family member was exposed) from Z91.B (the patient was exposed in utero).
• HIV: the guideline text now cites B20 by its full title, Human immunodeficiency virus [HIV] disease.
• Chapter 1: Infections resistant to antibiotics separated from Sepsis, Severe Sepsis, and Septic Shock.
• Chapter 2: admissions/encounters heading revised to specify antineoplastic chemotherapy.
• Chapter 3: heading corrected to Diseases (from Disease) of the blood and blood-forming organs…
• Present on admission: wording clarifications for reporting and assignment of the POA indicator (Appendix I).