To the Editor: Coronary heart disease (CHD) risk prediction for primary prevention now focuses on multifactorial risk,1-3 and various risk calculation tools exist.1-3 The need for such tools depends on the degree to which risk status can be estimated by healthcare professionals. We performed a study to assess general practitioners’ intuitive calculation of multifactorial CHD risk for patients likely to be considered for lipid-lowering therapy.

In 1999 we posted a survey to a random sample of 400 GPs in Victoria, and received back 155 completed surveys (39% response rate). The respondent population was demographically similar to the Australian GPs and trainees who billed Medicare in 1998–99. GPs were asked to estimate 5-year absolute risk of CHD for four vignettes (two primary prevention and two secondary prevention), each based on the average characteristics of a published lipid-lowering clinical trial cohort4-7 (vignette descriptions are available from the authors). For the primary prevention vignettes, GPs were also requested to estimate the risk relative to other Australians of the same age and sex. Estimated risks were compared with reported risks to derive risk ratios.

GPs accurately estimated the relative CHD risk for the two vignettes of patients with no prior CHD, with mean risk ratios of 0.84 (95% CI, 0.77–0.91) and 1.23 (95% CI, 0.97–1.49).

However, they overestimated absolute risk, with risk ratios ranging between 2.79 (95% CI, 2.61–2.96) and 6.43 (95% CI, 5.59–7.27). The proportion of GPs estimating within 10% of the actual risk was 9% for a 62-year-old man with prior CHD and average cholesterol level, 13% for a 60-year-old woman with prior CHD and high cholesterol level, 17% for a 55-year-old man with no prior CHD and high cholesterol level, and 43% for a 58-year-old man with no prior CHD and average cholesterol level. Although the two primary prevention vignettes had 5-year absolute CHD risks below 10%, most GPs’ estimates (93% and 71%, respectively) were greater than 10%.

In conclusion, GPs in Victoria have a good understanding of a patient’s relative risk of CHD, but they consistently overestimate absolute risk. The problem with absolute risk estimation may not be the sophisticated multifactorial calculations required, but rather a general overestimation of risk within the population, at least for middle age. The GPs’ estimates of absolute risk for the four vignettes were correctly ranked, suggesting that they recognised the degree to which a risk was lower or higher, but were unfamiliar with the scale. This overestimation led most GPs to categorise patients such as those from the AFCAPS/TexCAPS trial, with only a 3.3% 5-year risk of CHD,6 as having a risk of greater than 10%. GPs would therefore incorrectly consider these patients appropriate for lipid-lowering therapy according to national and international guidelines. 1-3 Education may improve understanding and accuracy of risk communication for CHD in middle-aged patients, but tools for accurate assessment of coronary risk are needed in routine clinical practice.