Selective recording in blood pressure readings may increase subsequent mortality.

BACKGROUND

Rounding blood pressure (BP) to the nearest 10 mmHg (terminal digit preference) and selecting for particular values near treatment cut-offs (number preference) have both been previously described. Both reduce measurement accuracy, and may have consequences for treatment and survival.

AIM: To check for number preference in screening for hypertension, and whether this influenced subsequent mortality.

DESIGN

Prospective case-control screening study.

METHODS

In the General Practice Hypertensive Study Group (GPHSG), prospective case control study patients (n=23 574) were screened on one occasion for high phase-IV diastolic BP (DBP4) (> or =90 mmHg). Identified cases were matched with normotensive controls for age, sex, date of screen and ethnic group, and were registered for mortality follow-up (n=6310). Patients with a high DBP4 had two further readings, and were treated if it remained elevated.

RESULTS

For DBP4 terminal digit, '0' was over-represented (28.2% vs. 20%), and the number '88' was over-represented in both men and women. There was an excess adjusted death rate for females with DBP4 88-89 mmHg vs. 90-99 mmHg for both cardiovascular (RR 2.56, 95%CI 1.43-4.56, p=0.0015) and all-cause (1.56, 95%CI 1.06-2.29, p=0.023) mortality. For males, the corresponding rates were non-significantly reduced: cardiovascular RR 0.69, 95%CI 0.42-1.14, p=0.15; all-cause RR 0.93, 95%CI 0.68-1.27, p=0.64.

DISCUSSION: The quality of BP measurements should be monitored both in research studies and in clinical practice as part of clinical governance procedures.