The International Classification of Diseases (ICD) is an ever-present factor and often irritant in the lives of clinicians. Although physicians view ICD codes as necessary for reimbursement claims, in fact they are also used for developing mortality data, influencing the development of health care policy, pointing directions for basic and applied research, and assisting in the decisions regarding allocation of resources for research and development. The ICD further serves as a classification system for causes of death and includes rules for coding causes of death, standardization of definitions such as “underlying cause of death,” tabulation lists that recommend the cause-of-death groupings used to present mortality data that can be compared among countries, formatting of the medical certification of death that is part of every death certificate in the United States, and the compilation and publication of statistics on diseases and causes of death.

It is our impression that the average physician spends considerable time battling with the choice of appropriate codes that poorly correspond to current disease concepts. Physicians in general, however, have no idea how these codes were developed and spend very little time pondering the process by which the ICD has been developed.

The primary sponsor of the ICD is the World Health Organization in collaboration with approximately 10 centers, primarily from Europe.1 The ICD was introduced in the late 19th century. The 9th revision of the ICD (ICD-9), used in the United States from 1979 until 1998 (the 10th revision (ICD-10) is currently being implemented), has proven woefully inadequate for appropriately identifying high blood pressure and hypertensive heart disease. A personal favorite is 401.1, “benign hypertension with heart failure.” Many of us have had considerable difficulty in considering hypertension as “benign,” and are not sure what “malignant” hypertension indicates as an isolated entity. Is this the presence of metastatic vascular hypertrophy? Table compares existing ICD-9 codes with the ICD-10 codes that are currently being implemented. Unfortunately, beginning with the title of the table, ie, “Essential Hypertension,” the coding still leaves much to be desired. Attempts have been made for years to expunge the archaic concept of “essential” when describing this greatest of cardiovascular health problems, and yet in remains in IDC-10.

Table TABLE.   Essential Hypertension
  1. Abbreviations: ICD-9-CM, International Classification of Diseases, Ninth Revision, Clinical Modification; ICD-10-CM, International Classification of Diseases, Tenth Revision, Clinical Modification.

401.9: Essential hypertension, unspecified110: Essential (primary) hypertension
Alphabetic index entries
Malignant 401.0Benign 401.1Unspecified 401.9None
Tabular entries
401: Essential hypertension110: Essential (primary) hypertension
 Includes Includes
  High blood pressure  High blood pressure
  Hyperpiesia  Hypertension (arterial) (benign) (essential) (malignant) (primary)
  Hyperiesis hypertension (arterial)  Systemic
 Excludes Excludes involving vessels of
  Elevated blood pressure without diagnosis of hypertension (796.2)  Brain (160–169)
  Pulmonary hypertension (416.0–416.9)  Eye (H35.0)
  That involving vessels of:    Brain (430–438)    Eye (362.11)
Code differences
 Hypertension table No hypertension table
 Classification by type Hypertension no longer classified using those terms; hypertension does not use type as defining classification
Elevated blood pressure reading without diagnosis of hypertension
 769.2: Elevated blood pressure without diagnosis of hypertension R03.0: Elevated blood pressure reading, without diagnosis of hypertension
 796.3: Nonspecific low blood pressure reading R03.1: Nonspecific low blood pressure reading

On a very practical note for the hypertension specialist, the ICD code will influence reimbursement. Now that the National Uniforms Claims Commission has granted the hypertension specialist a taxonomy code, medical billing will include this code along with level of service and applicable current procedural codes. Resistant hypertension has been designated as 997.91 in the ICD-9 codes. Unfortunately, there is no designation for “resistant hypertension” in the ICD-10 despite the increasing recognition of resistant hypertension as a major clinical entity, which, by definition, should indicate a more complex level of service. At this time, resistant hypertension must be dealt with by adding complexity of illness codes, ie, by definition resistant hypertension is a highly complex illness.

At least there is now an understanding that hypertension is a disease and that blood pressure is a biomarker. Thus, the white-coat effect can be coded with the designation R03.0, “elevated blood pressure without hypertension.” This gives hope that the definition of hypertension written by the American Society of Hypertension Writing Group that describes hypertension in stages defined not only by blood pressure, but importantly by the presence of associated cardiovascular risk factors and target organ damage, will eventually be adopted by future ICD codes.

Matching the ICD-10 codes with the different current procedural terminology codes will require some negotiating. However, this is a welcome problem considering the difficulties hypertension specialists have had in claiming reimbursement in the past. As an example of this, the Centers for Medicare & Medicaid Services currently reimburses ambulatory blood pressure measurement (ABPM) only if performed in conjunction with ICD-9 code 796.2 (ICD-10 R03.0). It has been reported that when patients with diagnoses of resistant hypertension are evaluated with ABPM, as many as one third are actually found to be controlled, yet there is currently no ICD-10 designation and no approved reimbursement for ABPM. We believe that when a hypertension specialist orders an ABPM, third-party payers should reimburse for this service since the procedure is clearly cost-effective in the evaluation of the white-coat effect and resistant hypertension, as well as improving the care of patients. In fact, the current National Institute for Clinical Excellence guidelines published in the United Kingdom suggests ABPM for all patients being treated for hypertension.

Now is a good time for the American Society of Hypertension to convene a group to look to future ICDs. It takes about 10 years for changes to be made; now is not too early to begin. Appropriate coding is essential not only for patient care but for planning future research needs. This is much too important a task to leave for someone else to do.


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  2. Reference
  • 1
    New International Classification of Diseases (ICD-10): the History and Impact. Brief Health Statistics Section. Colorado Department of Public Health and Environment, March 2001, No. 41.