Validity of self blood pressure measurement in the control of the hypertensive patient: factors involved

BACKGROUND: Improving clinical practice aimed at controlling hypertension is a pending issue in health systems. One of the methods currently used for this purpose is self blood pressure measurement (SBPM) whose use increases every day. The aims of this study are to establish the optimal cut-off point for the 3-day SMBP protocol and to identify factors that could affect the precision of the 3-day SMBP protocol using 24-h ambulatory blood pressure monitoring (ABPM) as a reference. METHOD: This is a cross-sectional descriptive study to validate a diagnostic test performed by a primary care team in Murcia, Spain. A total of 153 hypertensive patients under 80 years of age who met the inclusion criteria were evaluated. ABPM was performed for 24 h. The SBPM protocol consisted of recording 2 measurements in the morning and 2 at night for 3 days. RESULTS: The cut-off point for SBP was set at 135 mmHg (sensitivity: 80.39%, specificity: 74.19%), and for DBP, it was set at 83 mmHg (sensitivity: 76.48%, specificity: 84.89%), which yielded the highest combined sensitivity and specificity. After carrying out the validation study with the new figures, we proceeded to establish which socio-demographic factors prevented a correct classification of patients. These errors were more common in male patients for the assessments of both DBP (OR = 2.4) and SBP (OR = 2.5); hypertensive patients with age < 67,5 years (OR = 1,5); having no work activity (OR = 3,6) and with concomitant chronic kidney disease (CKD) (OR = 5.0). CONCLUSION: Being male, older than 67.5 years, with CKD or with no work activity increases the probability of being misclassified for hypertension during follow-up as assessed by SBPM over 3 days. TRIAL REGISTRATION: This study was approved by the research ethics committee of the University of Murcia under registration number 1018/2015.