Differences Based on 5th Digit Codes
In some circumstances, the International Classification of Diseases, Ninth Edition, Clinical Modification (ICD-9-CM) requires the coder to select a 5th digit code for a diagnosis based on chart information. The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) preserves several such instances of this; most familiar to psychiatrists is the selection of the 5th digit code for Major Depressive Disorder and Bipolar Disorder to indicate current severity of the mood episode. It turns out that ICD-9-CM has a number of other such 5th digit choices that are no longer reflected in the DSM-IV-TR because they represent distinctions that are not specifically recognized in the DSM-IV-TR or that have been superceded by more complex distinctions. DSM-IV-TR deals with this by automatically selecting "0" as the fifth digit. However, a coder following ICD-9-CM rules is supposedly obligated to choose the appropriate fifth digit code based on the patient's clinical information.
An example of this is seen in the 5th digit codes in ICD-9-CM for alcohol and drug dependence. The choices are "0=unspecified; 1=continuous, 2=episodic, and 3=remission." DSM-IV-TR does not care about "continuous vs. episodic" and employs much more complex remission specifiers than just saying "in remission". Thus, using the DSM-IV codes of 304.00 for alcohol dependence is, strictly speaking, inadequate because it does not take advantage of the 5th digit code when such information (such as the fact that the patient is in remission) exists. However, since 304.00 is in fact a legal ICD-9-CM code, it should not be rejected in a claim. The 5th digit code for alcohol dependence has not been used since the Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised (DSM-III-R); that is, since 1987, and psychiatrists have been submitting claims with 304.00 without known problems (Of note, this 5th digit was included in the Diagnostic and Statistical Manual of Mental Disorders, Third Edition (DSM-III) but dropped from DSM-III-R and DSM-IV).
Categories with 5th digit codes not used in DSM-IV-TR include: Schizophrenia and related disorders (categories 295.1x, 295.2x, 295.3x, 295.4x, 295.6x, 295.7x, and 295.9x), Pervasive Developmental Disorder (299.0x, 299.1x, 299.8x), and Alcohol/Drug Dependence/Abuse (305.0x, 305.2x, 305.3x, 305.4x, 305.5x, 305.6x, 305.7x, 305.9x).