Each space, typeface, indentation, and punctuation mark determines how you must interpret ICD-9-CM codes. These conventions were developed to help match correct codes to the diagnoses you encounter.
Standard ICD-9-CM coding conventions affect:
1. Terms and Instructions
2. Instructional Notes
3. ICD-9-CM Notes
I. Terms and Instructions
See directs coder to a more specific index term under which the correct code can be found.
Example: Cancerous- see Neoplasm, by site, malignant
See also refers to other index terms that may provide additional information for selecting a diagnostic code.
Example: Hematoma- see also Contusion
See category indicates that you should review the category specified in the index before selecting a code.
Example: Psychosis – see categories 295-298
This instruction is used in the tabular list for two purposes:
1. To code components of a procedure that are performed at the same time, and
2. To code the use of special adjunctive procedures or equipment.
Example: 03.90 Insertion of catheter into spinal canal, Code also any implantation of infusion pump (86.06)
For some operative procedures (listed in Volume 3), it is necessary to record the individual components of the procedure. In these instances, the alphabetic index lists both codes.
Example: 02.02 Elevation of skull fracture fragments, Code also any synchronous debridement of brain (01.59)
Terms that identify incisions are listed as main terms in the index. If the incision was made only for the purpose of performing further surgery, the omit code instruction is given.
As the abbreviation for “Not Elsewhere Classified”, NEC identifies codes and index terms that specify a condition or disease for which there is no other separate, more specific, code available to identify it.
Example: 518.82 Other pulmonary insufficiency, not elsewhere classified, Adult Respiratory Distress Syndrome NEC.
As the abbreviation for “Not Otherwise Specified,” NOS indicates the code is unspecified and, if possible, you should continue looking for a specific code, or you lack the information necessary to code the diagnosis to a more specific category.
Example: 558.9 Other and unspecified noninfectious gastroenteritis and colitis,
Colitis – NOS, dietetic, or noninfectious
Enteritis – NOS, dietetic, or noninfectious
Gastroenteritis – NOS, dietetic, or noninfectious
Ileitis – NOS, dietetic, or noninfectious
Jejunitis – NOS, dietetic, or noninfectious
Sigmoiditis – NOS, dietetic, or noninfectious
 Brackets enclose synonyms, alternate wording, or explanatory phrases.
Example: 286.5 Hemorrhagic disorder due to intrinsic circulating anticoagulants
Systemic Lupus Erythematous [SLE] inhibitor
() Parentheses enclose supplementary words that may be present or absent in the statement of a disease or procedure, without affecting the code number to which it is assigned.
Example: 780.64 Chills (without fever)
II. Instructional Notes
To assign diagnostic codes at the highest level of specificity, you must follow four kinds of instructional notes. These notes affect code descriptions in the Code Detail.
This note appears immediately under a three-digit code in the tabular list to further define or give an example of the contents of the category.
Example: 600 Hyperplasia of prostate, Includes – Enlarged Prostate
This note identifies terms in the tabular list that should not be coded under the referenced term. This note does not prevent you from using the excluded code in addition to the code from which it was excluded when both conditions are present.
Example: 600.1 Nodular prostate, Excludes – Malignant neoplasm of prostate (185)
Use additional code
This note appears in categories in the tabular list where you may add further information (by using an additional code) to give a more complete picture of the diagnosis from the available information.
Example: 281.2 Folate-deficiency anemia, Use additional E code to identify drug
Code first underlying disease
This instruction is used with codes in the tabular list that are not intended to be the principal diagnosis. The note requires that the underlying disease (etiology) be recorded first, and the particular manifestation second. Some possible underlying disease choices are listed following the instructional note with code references in parentheses. Always refer to the underlying disease in its own tabular section before coding it as the principal diagnosis to ensure that all other coding instructions are followed and the code is reported to its highest specificity level.
Example: 357.2 Polyneuropathy in diabetes, Code first underlying disease (249.6, 250.6)
ICD-9-CM notes affect both index terms in the Tabular Results window and code descriptions in the Code Detail. Notes in Volume 1 are indented and printed in plain type, while those in Volume 2 are boxed and italicized. The placement of these notes is as important as their content. Notes at the beginning of a section apply to all categories within the section. Those at the beginning of a subsection apply to all categories within the subsection. Notes preceding three digit categories apply to all fourth-digit and fifth-digit codes within that category.