What’s the Frequency, BP?

Abstract & Commentary

By Allan J. Wilke, MD, Professor and Chair, Program Director, Department of Family Medicine, Western Michigan University School of Medicine, Kalamazoo. Dr. Wilke reports no financial relationships relevant to this field of study.

Synopsis: A strategy of annual screening of blood pressure was as sensitive and more specific than the usual practice of measuring it at every office visit.

Source: Garrison GM, Oberhelman S. Screening for hypertension annually compared with current practice. Ann Fam Med 2013;11:116-121.

This retrospective case-control study looked at the family medicine patients from the Mayo Clinic in Rochester, MN, to determine whether measuring blood pressure (BP) annually is more specific and just as sensitive as measuring it at every visit. Patients were 18-75 years old, did not carry the diagnosis of hypertension (HTN), and had been active in the practice from 2005-10. They excluded patients with diabetes mellitus, coronary artery disease, and chronic kidney disease and who were pregnant or were taking antihypertensive medications for something other than HTN (e.g., migraine prophylaxis, peripheral edema).

Using International Classification of Diseases (ICD-9) billing code 401.x, they randomly selected 236 patients who were diagnosed with HTN (defined as a systolic BP [SBP] ≥ 140 or a diastolic BP [DBP] ≥ 90, average of at least two readings on at least two visits) during the study period and 500 who were not. Many patients were excluded from the study for either having only one elevated BP measurement, never having a diagnosis of HTN, or being diagnosed with HTN before the start of the study, but not having an ICD-9 401.x billing code. The final pools had 68 patients who were diagnosed with HTN during the study period and 372 who weren’t. The patients were similar in gender, smoking status, and number of visits per year, and differed in age, body mass index (BMI), and, not surprisingly, average BP. HTN patients were older (47.6 vs 41.2 years old), more obese (BMI 33.6 vs 28.6), and had higher SBP (135.3 vs 114.7) and DBP (82.7 vs 70.1). The two groups had 2.5 and 1.9 visits per year, respectively.

The authors compared two screening strategies. The first strategy (“usual”) measured BP at every visit. The second strategy (“annual”) was simulated. If the patient was being seen for a health maintenance visit, that BP was used. If no, and if the last BP was measured more than a year earlier, then that BP was used. The usual strategy identified all 68 HTN patients. It also identified 110 patients in the no-HTN group who had at least one BP ≥ 140/90. This yields a sensitivity of 100% (68/68, 95% confidence interval [CI], 92.2%-100%) and specificity of 70% (262/372, 95% CI, 65.2-75.0%). The annual strategy identified 63 HTN patients (sensitivity 93% [63/68], 95% CI, 83.7-97.6%), and 67 no-HTN patients with at least one BP ≥ 140/90 (specificity 82% [305/372], 95% CI, 77.7-85.8%). The sensitivities were not significantly different statistically, because the 95% CIs overlapped. The difference in specificities did reach statistical significance.

Commentary

The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC-7) recommends a screening interval of every 2 years for people who have BP < 120/80 and annually for people who are prehypertensive (SBP 120-139 or DBP 80-89).

The authors argue that the patients who were missed by the annual strategy would have eventually been diagnosed, and since end-organ damage from HTN occurs slowly, even delayed treatment would mitigate it. They also argue that the lower false-positive rate with annual screening (18% [67/372] vs 30% [110/372]) results in fewer patients undergoing a work up for HTN.

Measuring BP in the office is not the most accurate way of screening for HTN, and it may not be the most cost-effective.1 A meta-analysis published in 2011 compared ambulatory blood pressure monitoring (ABPM), the gold standard, to office and home monitoring, and found both to be lacking in sensitivity and specificity and recommended ABPM for individuals near the diagnostic cutoff, before subjecting them to lifelong medication management and its adverse effects.2 Retrospective, case-control studies at a single site are not the pinnacle of evidence-based medicine. I would not recommend that you change your modus operandi of screening for HTN based solely on this article. The best that can be said is that it generates questions that should be answered in double-blind, randomized, controlled studies. So why review this article? Three reasons. First, HTN is a factor in two of the top five causes of death (heart disease and stroke) in the United States in 20113 and treating HTN reduces mortality.4,5 Second, we desperately need to learn to work smarter, not harder. If, as a result of the Affordable Care Act, we are going to care for a much larger group of people in this country, many of whom are hypertensive, we have to change the way we do it. If this study is correct, we can shave valuable minutes off our visits by not measuring BP at every visit in a low-risk population (no diabetes, no heart disease, no kidney disease, no pregnancy). Finally, avoiding unnecessary work up (and expense) of false-positive diagnoses is vital if we are to make the best use of our limited resources.

We have all been waiting for publication of JNC-8. It was promised by the end of 2012.6 Keep your ear to the ground — word is that the diagnostic and treatment algorithms will be simpler than JNC-7.

References

1. Krakoff LR. Cost-effectiveness of ambulatory blood pressure: A reanalysis. Hypertension 2006;47:29-34.

2. Hodgkinson J, et al. Relative effectiveness of clinic and home blood pressure monitoring compared with ambulatory blood pressure monitoring in diagnosis of hypertension: Systematic review. BMJ 2011;342:d3621.

3. http://www.cdc.gov/nchs/fastats/lcod.htm. Accessed May 26, 2013.

4. Sheridan S, et al. Screening for high blood pressure: A review of the evidence for the U.S. Preventive Services Task Force. Am J Prev Med 2003;25:151-158.

5. Wolff T, Miller T. Evidence for the reaffirmation of the U.S. Preventive Services Task Force recommendation on screening for high blood pressure. Ann Intern Med 2007;147:787-791.

6. http://ahdbonline.com/article/new-jnc-8-hypertension-guidelines-be-released-year-end. Accessed May 26, 2013.