Coding for Hypertension
For The Record
Vol. 18 No. 2 P. 44

Hypertension is defined as a persistently elevated arterial blood pressure with a systolic pressure reading at rest that averages 140 millimeters of mercury or more, a diastolic pressure at rest that averages 90 millimeters of mercury or more, or both. Only the systolic or the diastolic pressure reading needs to be high for the physician to diagnose hypertension. Typically, hypertension does not cause any symptoms, but does increase the patient’s risk of certain diseases such as stroke, aneurysm, heart failure, myocardial infarction, and kidney damage.

Hypertension with no identifiable cause is called essential or primary hypertension and is the most common type of hypertension. Secondary hypertension is hypertension resulting from an underlying condition. Hypertension not otherwise specified is assigned to ICD-9-CM code 401.9. A mild, nonmalignant form of hypertension is termed benign hypertension (401.1). Malignant hypertension (also documented as accelerated hypertension) is a severe life-threatening form of hypertension with a diastolic pressure measuring above 120 millimeters of mercury and is classified to code 401.0.

A code for benign or malignant hypertension should not be assigned unless the physician documents the specific type in the body of the medical record. Documentation of hypertensive crisis or uncontrolled hypertension is not indicative of malignant hypertension. Without further clarification, assign code 401.9 for a diagnosis of hypertensive crisis or uncontrolled hypertension.

Hypertensive Heart Disease
Hypertensive heart disease (category 402) is a late complication of hypertension that affects the heart. From a coding standpoint, a code from category 402 is only assigned when the physician documents that the heart disease is due to the hypertension or when the heart condition is documented as hypertensive. In other words, a cause-and-effect relationship must be documented by the physician before a code from category 402 is assigned. If heart failure is present with the hypertensive heart disease, a code from category 402 is assigned with a fifth digit of 1. In addition, assign the appropriate code(s) from category 428 to identify the type of heart failure. More than one code can be assigned from category 428, if necessary, to completely identify the heart failure.

If the physician did not document a cause-and-effect relationship between the heart disease and the hypertension, then the two conditions are coded separately.

Hypertensive Kidney Disease
Category 403 classifies patients with hypertension and chronic kidney disease (585), renal failure (586), or renal sclerosis (587). If both conditions are present in the patient, a code from category 403 is assigned. No cause-and-effect relationship has to be documented by the physician. Only when the physician specifically documents that the renal disease is not due to the hypertension are these two conditions coded separately.

Effective October 1, 2005, there is a new coding directive added to category 403. It states, “Use additional code to identify the stage of chronic kidney disease (585.1-585.6), if known.” Therefore, if a patient is admitted with hypertension and stage 2 chronic kidney disease, then codes 403.91 and 585.2 are assigned. It is appropriate to add code 585.2 as a secondary diagnosis in this scenario to specify the stage of chronic kidney disease. However, if chronic renal failure not otherwise specified is documented with the hypertension, only assign code 403.91. It is not necessary to assign code 585.9 as an additional code as this code is outside of the range listed in the coding directive.

If a patient presents with acute renal failure and hypertension, it is necessary to assign two codes (584.9 and 401.9) because a causal relationship is not implied with these two conditions.

Secondary Hypertension
In secondary hypertension, the increased blood pressure is caused by another underlying condition such as:

• renal artery aneurysm;

• renal artery stenosis;

• pyelonephritis;

• glomerulonephritis;

• polycystic kidney disease;

• Cushing’s disease;

• coarctation of the aorta; and

• acute intermittent porphyria.

When coding secondary hypertension, two codes are required—one for the specified underlying condition and one from category 405 to identify the hypertension. Sequencing of these two codes will depend on the circumstances of admission. As with all the hypertension codes, the fourth-digit subcategory depends on whether the hypertension is specified as benign or malignant. If the physician does not specify whether the hypertension is benign or malignant, assign the code for unspecified.

Elevated Blood Pressure
If a patient has an elevated blood pressure reading, it does not necessarily mean the patient has hypertension. The coder should not assign a code for hypertension (401-405) based on an abnormal finding without supporting physician documentation. According to current coding guidelines, “For a statement of elevated blood pressure without further specificity, assign code 796.2, Elevated blood pressure reading without diagnosis of hypertension, rather than a code from category 401” (AHA Coding Clinic for ICD-9-CM, 2005, first quarter, page 48).

Typically, the physician will obtain multiple blood pressure readings at different times before establishing a diagnosis of hypertension. As always, code assignment is dependent on physician documentation.

Coding and sequencing for hypertension are dependent on the physician documentation in the medical record and application of the Official Coding Guidelines for inpatient care. Also, use specific AHA Coding Clinic for ICD-9-CM and American Medical Association CPT Assistant references to ensure complete and accurate coding.

— This information was prepared by Audrey Howard, RHIA, of 3M Health Information Systems (800-367-2447), a supplier of coding and classification systems to nearly 5,000 healthcare providers. The company and its representatives do not assume any responsibility for reimbursement decisions or claims denials made by providers or payors as the result of the misuse of this coding information.

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