QRISK may be less useful

Collins and Altman inappropriately criticise the National Institute for Health and Clinical Excellence (NICE) for not choosing QRISK to predict cardiovascular risk.1 In doing so, they do not distinguish between assessing individual cardiovascular risk (as used by clinicians) and predicting risk of cardiovascular events in an actively managed population (as used in public health planning). As most tools predicting cardiovascular risk were developed in actively managed populations, they will underestimate the risk that clinicians and patients are initially interested in: the risk if no further treatment is initiated. This distinction seems to be overlooked in most discussion of cardiovascular risk.

Most doctors would expect to explain the risk to patients were they left untreated. As with several other tools, however, QRISK was derived from a population cohort that may start additional treatments once found to have high rates of risk factors. Hence it is not surprising that it underpredicts cardiovascular risk. The Framingham study was conducted before the widespread use of effective treatment for cardiovascular risk factors and therefore its equations seem to overpredict cardiovascular risk when assessed in a population with active management of risk factors.

QRISK tried to adjust for baseline antihypertensive treatment, but its investigators admitted that this was a crude measure of blood pressure treatment.2 Furthermore, it did not adjust for patients who started treatment between baseline and the end of the study.

Although QRISK seems to be more accurate in predicting cardiovascular events in a contemporary UK population, it may be less accurate in communicating risk to patients. For risk communication and individual decisions, cardiovascular risk should be based on study populations that do not receive additional treatment for cardiovascular disease.