NICE clinical guidance requires diagnosis to be based both on readings taken in the clinic setting, as well as at home or over 24 hours with an ambulatory blood pressure meter.¹ The ‘white coat’ effect, where a patient is nervous about being in a clinical setting, can increase blood pressure levels by as much as 30mmHg.¹¹ As recent exercise can also raise blood pressure, three readings should be taken over a five-minute period after an initial resting period to get a better consistency.¹

While some clinicians regard SPRINT as a landmark study, the white coat effect raises questions about the methodology. Measurements were taken by a machine three times in a clinical setting, but as SPRINT trial health professionals were required not to converse with the patient during the resting period or between blood pressure readings, they would usually leave the consulting room before the patient conducted the blood pressure tests.¹³

The concern is that trial patients may have had artificially lower blood pressure levels due to the reduced white coat effect compared to normal practice with the health professional being present. The question is whether the findings can be generalised for the wider population.¹³