The minimum number of blood pressure measurements needed and thresholds for visit-to-visit blood pressure variability to predict cardiovascular disease in primary care patients

ObjectivesVisit-to-visit blood pressure variability (VVV BPV) is an underutilised risk factor for cardiovascular disease (CVD). This study aims to determine the minimum number of BP measurements needed and to identify cut-off values for the standard deviation (SD), coefficient of variation (CV), and average real variability (ARV) of systolic and diastolic VVV BPV to predict CVD risk in primary care. MethodsWe analysed data from the electronic practice-based research network (ePBRN) in Southwestern Sydney, including patients aged 18-55 with at least eight BP readings. Patients with incomplete data or no follow-up beyond age 55 were excluded. The agreement between SD calculated from 3-5 measurements and 8 measurements (reference) was evaluated using Pearsons correlation coefficient and the intraclass correlation coefficient. Then, after identifying that a minimum of five BP measurements is needed, another cohort with at least five BP measurements was developed. Percentile-based cut-offs (10th - 90 th, 5-percentile increments) were derived for systolic and diastolic BPV (SD, CV, ARV). Predictive accuracy was assessed using the C-statistic. The outcome was the first CVD occurrence. ResultsA total of 1,549 patients were included in the first study. Five BP measurements showed good agreement with eight measurements (ICC: 0.79; correlation: 0.80). A total of 3,022 patients were included (55.2% women). Higher VVV BPV (SD, CV. ARV) was associated with increased CVD risk. Optimal cut-off values for systolic BP were 19 mmHg (SD), 14% (CV), and 15 mmHg (ARV), and for diastolic BP were 11 mmHg (SD), 12% (CV), and 11 mmHg (ARV). Predictive performance was consistent across time frames. ConclusionsThese BPV cut-offs provide clinically relevant thresholds for CVD risk prediction. At least five BP measurements are sufficient to estimate BPV for this purpose.