Abstract P360: Diagnostic Accuracy Provided by Different Approaches to Office Blood Pressure Measurement: How Many Readings Are Enough?

Importance: Guidelines lack consensus about the optimal approach to measuring office blood pressure (BP) when screening for hypertension. Objective: To compare the accuracy provided by different office BP measurement approaches that differ based on number of office BP readings within a visit, number of visits, and assessment method. Design: Cross-sectional Setting: Primary care. Participants: 707 employees without prior diagnosis of hypertension or cardiovascular disease and with screening BP Measures: Six standardized BP readings were taken during each of 3 office visits at least 1 week apart, using 2 assessment methods (mercury sphygmomanometer and BpTRU oscillometric device) for a total of 12,645 readings. Confirmatory factor analysis was used to develop a model from which estimates of the probability of correctly classifying an individual’s office BP status using differing numbers and types of office BP readings were generated. Results: A single systolic BP reading correctly classified an individual as having BP above or below the cutpoint for elevated office BP (i.e. 140 mmHg) when the reading was 155 mmHg, respectively. Averaging three systolic BP readings across two visits correctly classified an individual 95% of the time if the averaged reading was 148 mmHg. There was more confidence gained by increasing the number of visits than the number of readings within a visit. There was no clinically significant confidence gained by dropping the first reading versus averaging all readings, nor by measuring with a manual mercury device versus with an automated oscillometric device. Limitations: Only evaluated research quality BP readings. Similar probabilities may not apply to BP measured in routine clinical practice. Conclusions and Relevance: Averaging BP readings across two or more office visits might best balance increased confidence in BP status with efficiency of BP measurement, though the preferred measurement strategy may vary with the clinical context. Patients with average readings modestly below the 140/90 mmHg cutpoint (e.g., 134-139 mmHg) might be appropriate for referral to out-of-office BP testing as one cannot gain strong confidence that their “true” office BP is below goal.