Blood pressure recording bias during a period when the Quality and Outcomes Framework was introduced

The 2004 UK Quality and Outcomes Framework (QOF) remunerates general practitioners for achieving a target blood pressure (BP) of <= 150/90 mm Hg for patients with ischaemic heart disease, stroke and hypertension. Using the DIN-LINK GP database, we investigated whether introducing the target altered BP recording. We extracted 3 164 189 BP measurements from 236 467 patients, with the above diagnoses from 2000 to 2005. Treatment was assessed by Read codes indicating prescriptions for antihypertensive drugs. Over this period, recorded systolic BP (SBP) fell: 36% had an SBP >150 mm Hg in 2000-2001, and only 19% in 2004 2005. However, there was a trend towards recording systolic values just below, rather than just above the 150 cut-off. In 2000-2001, 2.3% of patients had 148-149 recorded and 1.8% had 151-152. In 2004-2005, the figures were 4.2 and 1.3%, respectively. By smoothing the distribution we estimate that the true percentage of patients with SBP>150 mm Hg in 2004-2005 was 23%, rather than the 19% recorded. Moreover, patients with a recorded SBP = 148-149 were more likely to have a recorded diastolic BP <= 90 (93%) than patients with SBP = 151-152 (78%). However, patients just below the 150 mm Hg cut-off received more antihypertensive treatment than those just above it (odds ratio = 1.20, 95% confidence interval 1.01-1.41). We conclude that blood pressure levels in UK primary care have continued to fall through the introduction of QOF, offering significant public health benefits in the future. This fall has been exaggerated due to values being clustered just below the QOF target, but there is no evidence of adverse effects of this on clinical management. Journal of Human Hypertension (2009) 23, 764-770; doi: 10.1038/jhh.2009.18; published online 12 March 2009