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ICD-10-CM Guidelines for Coding and Reporting

ICD-10-CM Guidelines for Coding and Reporting


Guidelines for coding and reporting with ICD-10-CM are provided by the Centers for Medicare and Medicaid Services (CMS) and the National Center for Health Statistics (NCHS). These guidelines have been approved by the four organizations that make up the Cooperating Parties for the ICD-10-CM: the American Hospital Association (AHA), the American Health Information Management Association (AHIMA), CMS, and NCHS. The conventions of ICD-10-CM take precedence over these guidelines, however.

Basic ICD-10-CM Coding Steps

Step 1: Locate the Code

To locate the code, the coder must find the diagnosis, condition, or reason for visit in the Alphabetic Index and verify the provided code in the Tabular List. The coder has to follow all instructional notes (Leon-Chisen, 2011).

Step 2: Assign Code to the Highest Level

For maximum reimbursement and to prevent claim denials, the coder must assign the code to the highest level of detail. This is accomplished by:

  • Assigning a three-character code only if there are no four-character codes listed.

  • Assigning a four-character code only when there are no five-character codes in that subcategory.

  • Assigning a five-character code only when there are no six-character codes in that subcategory.

  • Assigning a six-character code when one such subclassification is provided.

  • Assigning a seven-character code extension when provided (Leon-Chisen, 2011). 

Step 3: Assign Residual Codes

The use of NEC and NOS (residual codes) as appropriate involves using the main term entry in the Alphabetic Index that is followed by a code number for the unspecified condition. This code is never used when subterms exist that allow for use of a more specific code (Leon-Chisen, 2011).

Step 4: Assign Combination Codes

If available, the coder should assign combination codes, which are codes used to classify either two diagnoses with associated secondary process or a diagnosis with an associated complication. Combination codes are listed in the Index and contain connecting words such as "due to," "with," and "associated with" (Leon-Chisen, 2011).

Step 5: Assign Multiple Codes

Multiple coding is the use of more than one code for the identification of certain elements of a complex diagnostic or procedural statement. These statements connect words and phrases by using "with," "incidental to," and "secondary to." Special circumstances related to multiple coding include:

  • Mandatory multiple coding – This type of coding is used for "dual classification," which describes the required assignment of two codes to give information about manifestations and/or characteristics and the associated underlying condition, disease, and/or etiology. These codes are found in the Alphabetic Index by the use of a second code listed in brackets.

  • Discretionary multiple coding – This type of coding involves "code first" notes that appear in the Tabular List. These notes are under certain codes that are not specifically manifestation or characteristic codes, but codes in which the condition may be due to the underlying condition, disease, illness, or cause. The underlying condition should be always sequenced first with these codes.

Example: Malignant ascites (R18.0) has a note that specifies "code first" the malignancy, such as malignant neoplasm of ovary (C56.-). For this encounter, code C56.- would be listed first, followed by code R18.0.

  • Indiscriminate multiple coding – The coder should avoid indiscriminate coding of irrelevant information, such as codes for characteristics of the diagnosis and codes based on findings of diagnostic tests unless confirmed by the physician (Leon-Chisen, 2011).

Step 6: Code Unconfirmed Diagnosis

For inpatient admissions that are listed as "possible," "probable," or "questionable," the coder should report as though the diagnosis was established. The exception to this step is when coding HIV infection and influenza due to certain identified viruses, such as avian flu or H1N1 virus (Leon-Chisen, 2011).

General Equivalence Mappings

CMS and the CDC created a national version of the General Equivalence Mappings (GEMs) to ensure that there is national data consistency. The GEMs are a tool that coders use to convert data from the ICD-9-CM to ICD-10-CM and ICD-10-PCS (forward mapping), as well as to convert the ICD-10-CM and ICD-PCS to ICD-9-CM (backward mapping). The GEMs are basically a comprehensive translation dictionary used for accurate and effective translation of any ICD-9-CM-based data used for tracking quality, calculating reimbursement, recording morbidity and mortality, or for converting applications (Davis, 2011).

ICD-10-CM and ICD-9-CM Chapter Comparison

ICD-10-CM Chapter

ICD-10-CM Code Categories

ICD-9-CM Code Categories

Certain Infectious and Parasitic Disease


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Disease of the Blood and Blood-Forming Organs and Certain Disorders involving the Immune Mechanism



Endocrine, Nutritional, and Metabolic Diseases



Mental and Behavioral Disorders



Disease of the Nervous System




Disease of the Eye and Adnexa



Disease of the Ear and Mastoid Process



Disease of the Circulatory System



Disease of the Respiratory System



Disease of the Digestive System



Disease of the Skin and Subcutaneous Tissue



Disease of the Musculoskeletal System and Connective Tissue



Disease of the Genitourinary System



Pregnancy, Childbirth, and the Puerperium



Certain Conditions Originating in the Perinatal Period



Congenital Malformations, Deformations, and Chromosomal   Abnormalities



Symptoms, Signs, and Abnormal Clinical Laboratory Findings, Not Elsewhere Classified



Injury, Poisoning, and Certain other Consequences of External Causes



External Causes of Morbidity



Factors Influencing Health Status and Contact of Health Services




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