Hypertension is the medical term for elevated blood pressure — a serious medical condition in which the pressure of the circulating blood against the arterial walls is high enough that it may eventually cause health problems such as hypertensive heart disease and stroke. Hypertension (HTN) is a worldwide epidemic, affecting an estimated 1.13 billion people globally and nearly half of all adults in the United States. That’s roughly 108 million Americans, and only about one in four have their blood pressure under control.

Coding for hypertension requires attention to detail and a solid understanding of the ICD-10-CM Official Guidelines for Coding and Reporting. One concept integral to proper coding of high blood pressure is guideline I.A.15, which states that the words “with” and “in” in ICD-10-CM should be interpreted to mean “associated with” and “due to” when either appears in a code title, the Alphabetic Index, or an instructional note in the Tabular List. A causal relationship between the two conditions is presumed when they are linked by these terms in the code book.

Let’s practice applying this concept to arrive at the correct codes for reporting different clinical scenarios involving patients with HTN.

ICD-10-CM classifies HTN by type as essential or primary (categories I10–I13) and secondary (category I15). Report code I10 Essential (primary) hypertension for individuals who meet the criteria for hypertension and do not have any comorbid cardiac or renal disease. This code includes “high blood pressure” but is not meant to be used when elevated blood pressure is noted in an individual that has not been diagnosed with HTN. Report cases of transient HTN with R03.0 Elevated blood-pressure reading, without diagnosis of hypertension.

If HTN progresses to the point where it’s affecting a body system, combination codes come into play. Specifically, the code set addresses Hypertensive heart disease with category I11, Hypertensive chronic kidney disease with category I12, and Hypertensive heart and chronic kidney disease with category I13.

When assigning diagnosis codes for HTN, there is a presumptive cause-and-effect relationship between HTN and heart involvement and between HTN and kidney involvement, as the two conditions are linked by “with” in the Alphabetic Index. ICD-10-CM Guideline I.C.9.a instructs that even in the absence of provider documentation explicitly linking them, these conditions should be coded as related unless the documentation clearly states the conditions are unrelated.

Hypertensive heart disease can cause serious health problems and is the No. 1 cause of death associated with HTN. It refers to heart conditions caused by elevated blood pressure. The heart working under increased pressure causes a variety of cardiac disorders including heart failure, coronary artery disease, and thickening of the heart muscle (hypertrophy of the myocardium).

A code from category I11 Hypertensive heart disease is assigned when an individual has hypertensive heart disease — HTN with cardiac condition(s), classified to I50.- or I51.4–I51.9. Since ICD-10-CM presumes a causal relationship between HTN and cardiac involvement, a combination code is used to reflect that they’re related even if there is no provider documentation linking them.

Category I11 is subdivided to indicate whether heart failure is present:

I11.0     Hypertensive heart disease with heart failure

I11.9     Hypertensive heart disease without heart failure

When a patient has heart failure and HTN, code first I11.0 as instructed by the note at category I50 Heart failure. An additional code from category I50 is required to specify the type of heart failure, if known. In cases where the type of heart failure is not identified, report I50.9 Heart failure, unspecified. The codes for systolic, diastolic, and combined heart failure also require a fifth digit to specify the acuity of the diagnosis:

0 – Unspecified

1 – Acute

2 – Chronic

3 – Acute on chronic

If the provider specifically documents a different cause for the heart condition unrelated to high blood pressure, then the HTN and heart condition should be coded separately and not linked via a combination code. In such cases, sequence according to the circumstances of the admission/encounter.

Example: A patient is discharged with a diagnosis of exacerbated chronic diastolic congestive heart failure and a secondary diagnosis of hypertension. Codes reported:

I11.0     Hypertensive heart disease with heart failure

I50.32   Chronic diastolic (congestive) heart failure

When the diagnostic statement includes both HTN and a condition classifiable to category N18 Chronic kidney disease, ICD-10-CM presumes a causal relationship and categorizes the condition as hypertensive chronic kidney disease (CKD). Use a code from category I12 to describe these two related disorders, even in the absence of documentation linking them. A fourth character is used with category I12 to indicate the stage of CKD.

Sequence first the I12 code for the combined diagnosis of HTN with CKD:

I12.0     Hypertensive chronic kidney disease with stage 5 chronic kidney disease or end stage renal disease

I12.9     Hypertensive chronic kidney disease with stage 1 through stage 4 chronic kidney disease, or unspecified chronic kidney disease

These two codes also require that you report a secondary code from category N18 to identify the stage of kidney disease, with documentation typically referencing the most recent estimated glomerular filtration rate (eGFR) — the best test to measure the level of kidney function and determine the stage of renal disease.

In cases where the documentation clearly states the CKD is not related to the HTN, the conditions should be coded separately. The guidelines further specify that if a patient has hypertensive chronic kidney disease and acute renal failure, an additional code for acute renal failure is required.

Example: A provider documents HTN and stage IIIb kidney disease based on the patient’s most recent comprehensive metabolic profile, which showed elevated blood urea nitrogen (BUN) and creatinine and an eGFR at 40 (mL/min/1.73m2). Repeat testing yields a similar result. Codes reported:

I12.9     Hypertensive chronic kidney disease with stage 1 through stage 4 chronic kidney disease, or unspecified chronic kidney disease

N18.32    Chronic kidney disease, stage 3b

If a patient has all three conditions documented — HTN, heart disease, and CKD — look to combination category I13 for code assignment. Codes for the three-disease combination are numerically arranged by the degree of CKD and then further differentiated by the presence or absence of heart failure.

I13.0     Hypertensive heart and chronic kidney disease with heart failure and stage 1 through stage 4 chronic kidney disease, or unspecified chronic kidney disease

I13.10   Hypertensive heart and chronic kidney disease without heart failure, with stage 1 through stage 4 chronic kidney disease, or unspecified chronic kidney disease

I13.11   Hypertensive heart and chronic kidney disease without heart failure, with stage 5 chronic kidney disease, or end stage renal disease

I13.2     Hypertensive heart and chronic kidney disease with heart failure and with stage 5 chronic kidney disease, or end stage renal disease

As with the two-disease combination codes, all of the three-disease combination codes require additional coding from category N18 to identify the stage of kidney disease. The three-combination codes that include heart failure also require an additional code from the I50 series to specify the type and acuity of the failure.

Example: The patient in the example above presents with new-onset moderate pedal edema, and, upon examination, the provider detects mild crackles bilaterally at the lung bases. An echocardiogram is ordered, which shows mild systolic heart failure. Her eGFR has remained stable. The provider documents all three conditions. Codes reported:

I13.0    Hypertensive heart and chronic kidney disease with heart failure and with stage 1 through 4 chronic kidney disease, or unspecified chronic kidney disease

I50.21   Acute systolic (congestive) heart failure

N18.32    Chronic kidney disease, stage 3b

Some patients have high blood pressure caused by another medical condition such as those that affect the kidneys, arteries, heart, or endocrine system. In these cases, the ICD-10-CM HTN codes discussed above cannot be used. Instead, turn to the codes in category I15 Secondary hypertension. The five secondary hypertension codes require that you also code the underlying condition. The first-listed code is determined based on the reason for the patient encounter.

Example: A patient is being seen for blood pressure management. The provider documents acromegaly — a hormonal disorder that develops when the pituitary gland produces too much growth hormone during adulthood — with secondary hypertension. Codes reported:

I15.2     Hypertension secondary to endocrine disorders

E22.0     Acromegaly and pituitary gigantism

All of the HTN codes require an additional ICD-10-CM code, such as F17 Nicotine dependence, if the patient is a current or former tobacco user. If there is no documentation that a patient who uses tobacco is “dependent,” then you would instead use the code for tobacco use (Z72.0). Occupational and environmental exposure to tobacco should also be reported if the provider believes these are influencing the patient’s health status. Codes include:

Z57.31   Occupational exposure to environmental tobacco smoke

Z77.22   Contact with and (suspected) exposure to environmental tobacco smoke (acute) (chronic)

Z87.891 Personal history of nicotine dependence

Diagnosis coding for hypertensive disorders may seem convoluted at first, as there are several categories of codes. But don’t stress; there are a limited number of codes for HTN — only nine codes for primary hypertension and five codes for secondary hypertension. So, there’s no reason to let determining proper code selection for HTN raise your blood pressure. All you have to do is take a deep breath and remember to look to, and follow, the ICD-10-CM coding guidelines.