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What is ICD-10-CM?

What is ICD-10-CM?


ICD-10-CM is a statistical classification system that arranges diseases and injuries into groups according to predetermined criteria. The ICD-10-CM system is used for billing in both inpatient and outpatient settings.

ICD-10-CM Tabular List of Diseases and Injuries

The main classification of diseases and injuries in the Tabular List consists of 21 chapters (see figure). Half of these chapters are based on conditions related to a specific body system and the other half of them are based on conditions classed by etiology. Additionally, Z codes represent factors that influence health status and contact with health services, which are recorded as diagnoses. The V, W, X, and Y codes are used to indicate the external causes of injuries and conditions.

The chapter titles of the ICD-10-CM table of contents are based on either anatomical site, etiology, or the circumstances of onset. The result is a classification system with multiple axes. Codes in the Tabular List are in numerical order, and references from the Alphabetic Index are by code number rather than page number. Code titles and numbers appear in body in the Tabular List.

Layout of ICD-10-CM Manual



ICD-10-CM Conventions

ICD-10-CM Official Guidelines for Coding and Reporting

ICD-10-CM Index to Disease and Injuries

ICD-10-CM Neoplasm Table

ICD-10-CM Table of Drugs and Chemicals

ICD-10-CM Index of External Causes

ICD-10-CM Tabular List of Disease and Injuries

 Chapter 1 – Certain Infectious and Parasitic Disease

 Chapter 2 – Neoplasms

 Chapter 3 – Disease of the Blood and Blood-Forming Organs and Certain Disorders involving the Immune Mechanism

 Chapter 4 – Endocrine, Nutritional, and Metabolic Diseases

 Chapter 5 – Mental and Behavioral Disorders

 Chapter 6 – Disease of the Nervous System

 Chapter 7 – Disease of the Eye and Adnexa

 Chapter 8 – Disease of the Ear and Mastoid Process

 Chapter 9 – Disease of the Circulatory System

 Chapter 10 – Disease of the Respiratory System

 Chapter 11 – Disease of the Digestive System

 Chapter 12 – Disease of the Skin and Subcutaneous Tissue

 Chapter 13 – Disease of the Musculoskeletal System and Connective Tissue

 Chapter 14 – Disease of the Genitourinary System

 Chapter 15 – Pregnancy, Childbirth, and the Puerperium

 Chapter 16 – Certain Conditions Originating in the Perinatal Period

 Chapter 17 – Congenital Malformations, Deformations, and Chromosomal   Abnormalities

 Chapter 18 – Symptoms, Signs, and Abnormal Clinical Laboratory Findings, Not Elsewhere Classified

 Chapter 19 – Injury, Poisoning, and Certain other Consequences of External Causes

 Chapter 20 – External Causes of Morbidity

 Chapter 21 – Factors Influencing Health Status and Contact of Health Services

Code Structure

All ICD-10-CM codes have an alphanumeric structure where all codes begin with a letter. There are three characters in the basic code structure, and the decimal point is used to separate the three character category code from the subcategory codes. The main classification is structured so that the following subdivisions are provided:

  • Sections – These are groups of three-character categories, such as infections of the skin and subcutaneous tissue (L00-L08).

  • Categories – These are three-character code numbers, such as cutaneous abscess, furuncle, or carbuncle (L02).

  • Subcategories – These are four-character code numbers, such as cutaneous abscess, furuncle and carbuncle of trunk (L02).

  • Five, six, or seven-character code numbers – These are the 5th, 6th, and 7th character subclassification, such as cutaneous abscess of abdominal wall (L02.211).

Example of Code Structure

Some codes have applicable seventh characters and are considered "codes" not "subcategories." A code that should have an applicable seventh character is considered invalid without that particular character listed.

K29 Gastritis and duodenitis                                                      (category)

         K29.0 Acute gastritis                                                             (subcategory)

                    K29.00 Acute gastritis without bleeding                     (code)


R10 Abdominal and pelvic pain                                                     (category)

         R10.8 Other abdominal pain                                                (subcategory)

                     R10.811 Abdominal tenderness                                   (subcategory)                  

                                   R10.811 Right upper quadrant tenderness        (code)                                    

Placeholder Characters

With ICD-10-CM, the letter "x" is used as the fifth character dummy placeholder for many six-character codes, as in T37.5x1 (poisoning by antiviral drugs, accidental). This is done to allow for expansion in the future, where the sixth character has a specific use. For example, the T36 thru T50 codes represent poisoning or adverse effects and the T51 thru T65 codes represent toxic effects. The sixth character in these categories represents the indent: accidental, assault, intentional self-harm, undetermined, underdosing, or adverse effect.

Example of Use of Placeholder

T37.5x1 = Poisoning by antiviral drugs, accidental

T37.5x2 = Poisoning by antiviral drugs, intentional self-harm

The use of the placeholder character "x" and the seventh-character extension is shown here:

T16 Foreign body in ear

Seventh-character extensions:

A: Initial encounter

D: Subsequent encounter

S: Sequela

T16.1 Foreign body in right ear

T16.2 Foreign body in left ear

T16.9 Foreign body in ear, unspecified

For a child who has a marble in the left ear, the encounter would be assigned a code of T16.2xxA. If the child comes back for a follow-up visit over the same problem, the encounter would be assigned a code of T16.2xxD. If the child has a complication resulting from this problem, the encounter would be coded as T16.2xxS.

Alphabetic Index

The alphabetic index includes the Index of Diseases and Injuries, the Index of External Causes of Injury, the Table of Neoplasms, and the Table of Drugs and Chemicals. Main terms represent diseases or injuries, and subterms represent site, type, or etiology of the diseases or injuries. For example, acute gastritis is listed under "Gastritis, acute." Exceptions to this include:

  • Congenital conditions are usually listed under the main term "Anomaly" rather than under the name of the condition or disease.

  • Pregnancy and childbirth complications are often found under such terms as "Delivery," "Puerperal," and "Pregnancy." They could also be listed under the main term for the condition that causes the complication where the subterm is referenced, as with "complicating pregnancy."

  • Late effects or complications related to an earlier condition are listed under "Sequelae."

  • The majority of medical and/or surgical care complications are listed under the term "Complications" rather than under the condition's name.

Pattern of the Alphabetic Index

  • Main terms – They are set far left of the margin, in bold type, and capitalized.

  • Subterms – They are indented one standard indention to the right, under the main term, printed in regular type, lower-case.

  • Specific subterms – They are indented farther right and listed in alphabetical order.

  • Dash – This is listed at the end of an index entry and indicates that additional characters are necessary.

Metrorrhagia N92.1                                                                       (main term)

 climacteric N92.4                                                                         (subterm)

 menopausal N92.4                                                                      (subterm)

 postpartum NEC (following delivery of placenta O72.1               (subterm)

      delayed or secondary O72.1                                                        (more specific subterm)                                                                             

Numeric Entries

The subterm entries for various words indicating numbers or those of numerical characters appear first under the appropriate main term. They are listed in alphabetical order in the spelled format. For instance, "Damage, nerve, fifth" will come before "Damage, nerve, third." The exception is when Roman numerals and Arabic numerals are used.

Facts about ICD-10-CM

  • ICD-10-CM codes have 3 to 7 digit alphanumeric codes.

  • As of October 1, 2013, ICD-10-CM codes are used on all health insurance claims.

  • ICD-10-CM codes describe diseases, illnesses, injuries, procedures, and signs/symptoms.

  • While most ICD-10-CM codes have one definition, some of them have more than one definition.

  • Accurate coding makes a significant difference in reimbursement (Davis, 2011).

Benefits of ICD-10-CM

The ICD-10-CM classification system offers many benefits. This coding measure will allow for improved:

  • Measurement of safety, quality, and efficacy of care

  • Designed payment systems and claims processing for reimbursement

  • Conducting of research, clinical trials, and epidemiological studies

  • Health policy

  • Strategic planning and healthcare delivery system design

  • Financial, clinical, and administrative performance

  •  Ability to track public health and risks for diseases

  • Prevention and detection of healthcare fraud and abuse

  • Monitoring of resource utilization (Davis, 2011)

ICD-10-CM vs. ICD-9-CM

If you know how to code using the ICD-9-CM system, then you already know how to use the ICD-10-CM system. The process remains the same, only the codes are different. The ICD-10-CM codes are based on medical record documentation, just like the ICD-9-CM codes. The code structure varies slightly, as does the code itself. The improved structure and specificity of the ICD-10-CM facilitates the development of electronic coding tools that can assist with accurate and fast code selection (Davis, 2011).

ICD-9-CM Code Structure







1st Digit

2nd Digit

3rd Digit


4th Digit

5th Digit











Etiology/Anatomic Site/Manifestation

Etiology/Anatomic Site/Manifestation

Total length: 3 to 5 digits

First character: Number or Letter (E/V)

Second thru fifth characters: Numbers only

Minimum length: 3 characters

Decimal: Positioned after third character

ICD-10-CM Code Structure

Letter Only

Number Only

Number or Letter


Number or Letter

Number or Letter

Number or Letter

Number or Letter

1st Digit

2nd Digit

3rd Digit


4th Digit

5th Digit

6th Digit

7th Digit













Etiology/Anatomic Site/Severity

Etiology/Anatomic Site/Severity

Etiology/Anatomic Site/Severity

Added code extensions

Total length: 3 to 7 digits

First character: Letter only

Second Character: Number only

Third thru seventh characters: Number or letter

Decimal: Positioned after third character

Letter format: Letters are case-sensitive

Similarities of ICD-10-CM and ICD-9-CM

  • Format – Both systems use a Tabular List and Alphabetic Index.

  • Chapters – Both Tabular lists are structured similarly, except with the ICD-10-CM, the Sense Organs are separated from the Nervous System chapter.

  • Indexes – Both Indexes are structured the same.

  • Codes – In both systems, codes are invalid if they are missing an applicable character.

  • Code Find – Codes are looked up the same way in both systems, with diagnostic terms from the Alphabetic Index and verified code number from the Tabular List.

  • Nonspecific Codes – Both systems use "unspecified" and "not otherwise specified" codes when a more specific code is not available (Davis, 2011). 

Differences between ICD-10-CM and ICD-9-CM

  • ICD-10-CM codes are more specific than ICD-9-CM codes

  • ICD-10-CM codes have letter and numbers (alphanumeric), with the 1wt character a letter.

  • ICD-10-CM codes are longer than ICD-9-CM codes, with up to 7 characters.

  • ICD-10-CM codes are more complete, so the coder does not need to refer back to the category or subcategory level.

  • ICD-10-CM has an expanded use of combination codes, with certain conditions and associated symptoms or manifestations.

  • ICD-10-CM groups injuries by anatomical site rather than injury type.

  • ICD-10-CM uses 7th character to provide information about the encounter characteristics. (The use of this character is needed for the code to be valid).

  • ICD-10-CM uses a dummy placeholder "x" to allow for future expansion and to fill out empty characters when there are less than 6 or when a 7th character applies.

  • ICD-10-CM includes two types of Exclusion Notes: Excludes1 and Excludes2 (Davis, 2011).

ICD-10-CM Format and Conventions

The official conventions and guidelines are located in the front of most ICD code books. Conventions are guidelines for how codes are selected and sequenced, and guidelines are instructions regarding assignment of codes in certain cases. With ICD-10-CM only includes the Tabular List of diseases for diagnoses (volume 1 of ICD-9-CM) and the Alphabetic Index to diseases and injuries (volume 2 of ICD-9-CM). Conventions are guidelines for how codes are selected and sequenced. The ICD-9-CM volume 3 (procedure codes) is replaced with the ICD-10-PCS.  ICD-10-CM conventions include: 

  • Instructional notes

  • Abbreviations

  • Cross-reference notes

  • Punctuation marks

  • Relational terms ("due to" "and" "without") (Grebner & Suarez, 2013)

Instructional Notes

Instructional notes are general notes, inclusion and exclusion notes, "code first" notes, "use additional codes" notes, and "code also" notes.

  • General notes – These are listed in the Tabular List of Diseases and Injuries. They provide general information code usage in specific sections, such as an explanation that certain chapter codes are used only for maternal records but not newborn records.

  • Inclusion and exclusion notes – With ICD-10-CM, it is often necessary for the coder to indicate when certain conditions are or are not included. This is done by use of inclusion and exclusion notes. Inclusion notes are always introduced with "includes" when they are placed at the beginning of a section. Exclusion notes are always introduced with "excludes," with excluded conditions listed in alphabetical order.

  • "Code first" note – This note is found at the manifestation code and they provide instructions that the underlying condition must be sequenced first. 

  • "Use additional code" note – This note is found at the etiology code and is a clue to identify the manifestations associated with the condition. 

  • "Code also" note – This note indicates that two codes may be required to adequately describe a particular condition. The sequencing order relies on the encounter purpose and the severity of the condition.


The two main abbreviations of the ICD-10-CM are NEC (not elsewhere classified) and NOS (not otherwise specified). Explanation:

  • NEC – This abbreviation is used to indicate that there is no separate code for the condition regardless of the specificity t of the diagnosis. For example, a disease of the pleura listed as a hydropneumothorax is included in the code J94.8, Other specified pleural conditions. 

  • NOS – This abbreviation is the equivalent of "unspecified" and should be used only when neither the diagnostic statement nor medical record provides information that permits specific classification. These codes are usually classified to codes with a fourth or sixth character "9" and fifth character "0." Sometimes, conditions that are listed as both NOS and "unspecified" are combined into one code.

Punctuation Marks

The ICD-10-CM uses several punctuation marks, which have specialized meanings that are different to the usual English language usage. Explanation:

  • Parentheses – The ICD-10-CM uses parentheses to enclose supplementary words or explanatory information. The words and/or information may be either absent or present in the diagnosis statement and do not affect the code. These terms are recognized as "nonessential modifiers," which are used to indicate that terms in parentheses are included in the code but do not need to be listed in the diagnosis. The terms enclosed in parentheses serve only as reassurance that the coder has found the right code. Example:

The main term "Pneumonia" has numerous nonessential modifiers that are enclosed in parentheses. A diagnosis of "Acute Pneumonia" and "Acquired Pneumonia" are both coded J18.9 because both terms are listed in parentheses as nonessential modifiers.

  • Square Brackets – The ICD-10-CM uses square brackets to enclose synonyms, abbreviations, alternative words, and explanatory phrases. Found in the Tabular List, square brackets provide additional information to the coder. Example: "Human Immunodeficiency Virus [HIV]." In the Alphabetic Index, square brackets indicate that the number is a manifestation and another number must be assigned first for the underlying code. Thus, the code in brackets advises that both conditions must be used, and that code can never be assigned as the main diagnosis. Example:


       Sickle cell D57.-[N08] 

The entry "Nephropathy, sickle cell D57-[N08]" where the first code is the underlying disease and the enclosed code is a manifestation.

  • Colons – The ICD-10-CM uses colons in the Tabular List in the inclusion and exclusion notes. They are listed after an incomplete term that needs one or more modifiers. Example:

N92.6 Irregular menstruation, unspecified

            Irregular bleeding NOS

            Irregular periods NOS

            Excludes 1: irregular menstruation with:

                                lengthened intervals or scanty bleeding (N91.3-N91.5)

                                shortened intervals or excessive bleeding (N92.1)

In the Tabular List under exclusion statement for code N92.6, the colon follows the subterms "irregular menstruation with," indicating that the code N92.6 is excluded with it is described as irregular menstruation with lengthened intervals or scanty bleeding or irregular menstruation with shortened intervals or excessive bleeding.

Cross-Reference Notes

Cross-reference notes advise the coder to look somewhere else before assigning a code. These notes are found in the Alphabetic Index and include "see," "see also," "see category," and "see condition." Explanation:

  • "See" – The "see" cross-reference indicates that the coder must use an alternative term. A coder must follow this advice, as it is mandatory. Example: The entry for "Hemarthrosis, traumatic" uses a cross-reference not to direct the coder to the entry for "sprain."

  •  "See also" – The "see also" cross-reference indicates that the coder can refer to another place in the Alphabetic Index to find a code for the specific condition or procedure. However, if the original entry provides all necessary information, the coder does not have to follow the cross-reference. Example: The term "Psychoneurosis" directs the coder to "see also" the term "Neurosis."

  • "See category" – The "see category" cross-reference offers the coder a category number. This is listed in the Tabular List, where the coder selects a code from the available options. Example: The entry "Examination, prenatal" directs the coder to category O34.

  • "See condition" – The "see condition" cross-reference advises the coder to the main term related to the condition. This is used when the coder has reference the adjective rather than the main term (noun form) for the actual condition. Example: The entry is "Arterial Thrombosis," and the coder references the main term "Arterial." The note will direct the coder to "see condition" of "Thrombosis".

Relational Terms

Relational terms of ICD-10-CM include "and," "with," and "due to."

  • "And" – The word "and" means both "and" and "or" when it is found in the code title.

  • "With" – The word "with" means "associated with" or "due to" when it is found in the code title and as an instructional note in the Tabular List. In the Alphabetic Index, the word "with" is sequenced immediately following the main term.

  • "Due to" – The words "due to" in both the Tabular List and the Alphabetic Index means that there is a casual relationship between two conditions. This assumption occurs when both conditions are present or when the diagnostic statement indicates this relationship.


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