ICD-10-CM Basics

Selecting accurate diagnosis codes using ICD-10-CM is challenging due to the availability of more than 68,000 codes. In this article, we shared general coding guidelines for ICD-10-CM which will help you in selecting accurate diagnosis codes. Before we proceed with coding guidelines, you’ll need access to two sets of lists in ICD-10 CM i.e., the Alphabetical Index of diagnostic terms and the Tabular List of ICD-10 codes. The Alphabetical Index of diagnostic terms lists thousands of ‘main terms’ alphabetically. Under each of those main terms, there is often a sub-list of more-detailed terms, for instance, ‘Cataract’ has a sub-list of 84 terms. The Tabular List of ICD-10 codes is organized alphanumerically from A00.0 to Z99.89. It is divided into chapters based on body parts or conditions.

General Coding Guidelines for ICD-10-CM

Locating a code in the ICD-10-CM 

To select a code in the classification that corresponds to a diagnosis or reason for a 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 in 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 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.

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 for 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. 

Combination Code 

A combination code is a single code used to classify: two diagnoses, a diagnosis with an associated secondary process (manifestation); or a diagnosis with an associated complication. Combination codes are identified by referring to sub-term 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 the 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.

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. 

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 sub-terms are listed, assign the given code. 
• If the sub-terms are not listed, code the existing underlying condition(s) and not the condition described as impending or threatened.

Remaining Coding Guidelines for ICD-10-CM

• The appropriate 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.
• Codes that describe symptoms and signs, as opposed to diagnoses, are acceptable for reporting purposes when a related definitive diagnosis has not been established by the provider.
• Signs and symptoms that are associated routinely with a disease process should not be assigned as additional codes unless otherwise instructed by the classification.
• Additional signs and symptoms that may not be associated routinely with a disease process should be coded when present.
• If the same condition is described as both acute (sub-acute) and chronic, and separate subentries exist in the Alphabetic Index at the same indentation level, code both and sequence the acute (sub-acute) code first.
• 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 by the same ICD-10-CM diagnosis code.
• 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 sides. If the side is not identified in the medical record, assign the code for the unspecified side.
• 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). 

MedicalBillersandCoders (MBC) is a leading medical billing company providing complete billing and coding services. We shared general coding guidelines for ICD-10-CM for provider education purposes, you can refer to the following link for a detailed understanding. In case any assistance is needed for medical billing and coding, contact us at 888-357-3226 / [email protected]

Reference: ICD-10-CM Official Guidelines for Coding and Reporting FY 2023

ICD-10 CM Copyright @World Health Organization (WHO) 

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