Detection of masked hypertension by home blood pressure measurement:: is the number of measurements an important issue?

Background Office blood pressure (OB P) and home blood pressure (HBP) enable the identification of patients with masked hypertension. Masked hypertension is defined by normal OBP and high HBP and is known as a pejorative cardiovascular risk factor. Objective The objective was to evaluate in the SHEAF study the influence of the number of office or home blood pressure measurements on the classification of patients as masked hypertensives. Methods Patients with OBP <140/90 mmHg (mean of six values: three measurements at two separate visits, V1 and V2) and H B P >135/85 mmHg (mean of all valid measurements performed over a 4-day period) were the masked hypertensive reference group. The consistency of the classification was evaluated by using five definitions of HBP values (mean of the 3, 6, 9, 12 and 15 first measurements) and two definitions of OBP values (mean of three measurements at V1 and mean of three measurements at V2). Results Among the 4939 treated hypertensives included in the SHEAF study, 463 (9.4%) were classified as masked hypertensives (reference group). By decreasing the number of office or home measurements, the prevalence of masked hypertension ranged from 8.9-12.1%. The sensitivity of the classification ranged from 94-69% therefore 6-31% of the masked hypertensives were not detected. The specificity ranged from 98-94% therefore 1-6% of patients were wrongly classified as masked hypertensives. Conclusion A limited number of home and office BP measurements allowed the detection of masked hypertension with a high specificity and a low sensitivity. A sufficient number of measurements (three measurements at two visits for OBP and three measurements in the morning and in the evening over 2 days for HBP) are required to diagnose masked hypertension. (C)) 2004 Lippincott Williams Wilkins.