Aim: To compare the calibration performance of the original Framingham Heart Study risk prediction score for cardiovascular disease and an adjusted version of the Framingham score used in current New Zealand cardiovascular risk management guidelines for high and low risk ethnic groups.
Methods: Since 2002 cardiovascular risk assessments have been undertaken as part of routine clinical care in many New Zealand primary care practices using PREDICT, a web-based decision support programme for assessing and managing cardiovascular risk. Individual risk profiles from PREDICT were electronically and anonymously linked to national hospital admissions and death registrations in January 2008. Calibration performance was investigated by comparing the observed 5-year cardiovascular event rates (deaths and hospitalisations) with predicted rates from the Framingham and New Zealand adjusted Framingham scores. Calibration was examined in a combined 'high risk' ethnic group (Maori, Pacific and Indian) and a European 'low risk' ethnic group. There was insufficient person-time follow-up for separate analyses in each ethnic group. The analyses were restricted to PREDICT participants aged 30-74 years with no history of previous cardiovascular disease.
Results: Of the 59,344 participants followed for a mean of 2.11 years (125,064 person years of follow-up), 1,374 first cardiovascular events occurred. Among the 35,240 European participants, 759 cardiovascular events occurred during follow-up, giving a mean observed 5-year cumulative incidence of 4.5%. There were 582 events among the 21,026 Maori, Pacific and Indian participants, corresponding to a mean 5-year cumulative incidence rate of 7.4%. For Europeans, the original Framingham score overestimated 5-year risk by 0.7-3.2% at risk levels below 15% and by about 5% at higher risk levels. In contrast, for Maori, Pacific, and Indian patients combined, the Framingham score underestimated 5-year cardiovascular risk by 1.1-2.2% in participants who scored below 15% 5-year predicted risk (the recommended threshold for drug treatment in New Zealand), and overestimated by 2.4-4.1% the risk in those who scored above the 15% threshold. For both high risk and low risk ethnic groups, the New Zealand adjusted score systematically overestimated the observed 5-year event rate ranging from 0.6-5.3% at predicted risk levels below 15% to 5.4-9.3% at higher risk levels.
Conclusion: The original Framingham Heart Study risk prediction score overestimates risk for the New Zealand European population but underestimates risk for the combined high risk ethnic populations. However the adjusted Framingham score used in New Zealand clinical guidelines overcompensates for this underestimate, resulting in a score that overestimates risk among the European, Maori, Pacific and Indian ethnic populations at all predicted risk levels. When sufficient person years of follow-up are available in the PREDICT cohort, new cardiovascular risk prediction scores should be developed for each of the ethnic groups to allow for more accurate risk prediction and targeting of treatment.