Quality indicators to measure blood pressure management over a time interval

Quality indicators are an important part of the primary care landscape, but focus strongly on point-in-time measurements, such as a patient's last blood pressure (BP) measurement. There is a larger space of possible measurements, including ones that more explicitly consider management over an interval of time.

To determine the predictive abilities of five different quality indicators related to poor BP control.

Data from two New Zealand general practices was analysed on five BP control indicators for patients with diagnosed hypertension: 1) last BP high (>150/90 mmHg); 2) last BP high or no BP measurement; 3) two or more consistently high BP measurements for ≥ 90 days; 4) a high BP then lapse of >120 days in BP measurement; and 5) antihypertensive medication possession ratio (MPR) of <80%. Probability that a patient would be identified by each indicator for the nine-month evaluation period ending 31 March 2009 was computed for each indicator one quarter, two quarters and three quarters prior to this date. Associations among the five indicators for the evaluation period were also calculated.

Positive predictive value (PPV) of indicators for the same indicator nine months later ranged from 27% (last BP high) to 64% (MPR). PPVs among the five measures with respect to the same time period ranged from 9% to 77% (median 33%).

Modest PPVs between indicators suggest the importance of considering multiple indicators to incentivise best management across diverse aspects of BP control.