New AHA/ACC risk calculator for cholesterol may overestimate risk for some patients: report

Two Harvard researchers identified problems with a risk calculator for cholesterol that was jointly introduced last week by the American Heart Association (AHA) and the American College of Cardiology (ACC) as part of new guidelines for the use of statins in the US. Nancy Cook and Paul Ridker say their calculations indicate the tool over-predicted cardiovascular risk by 75 percent to 150 percent when tested in populations that were followed for decades as part of research studies, adding that "such systematic overestimation of risk will lead to considerable over-prescription," and that "miscalibration to this extent should be…addressed before these new prediction models are widely implemented."

In their analysis, Cook and Ridker used data from three large studies of more than 100 000 healthy volunteers to compare how many of the participants had heart attacks or strokes over a 10-year period with the number predicted by the calculator. They said "it is possible that as many as 40 percent to 50 percent of the 33 million middle-aged Americans targeted by the new guidelines for statin therapy do not actually have risk thresholds exceeding the 7.5-percent level suggested for treatment." The researchers' findings will be published in The Lancet on November 19.

Cleveland Clinic cardiologist and former ACC president Steven Nissen described Cook and Ridker's findings as "very concerning," adding that "since the risk calculator was not previously published, it now makes sense to halt implementation of the guidelines so that independent physician scientists can evaluate the accuracy of the risk calculator." However, Sidney Smith, executive chairman of the guideline committee, acknowledged that Cook and Ridker's concerns "merit attention," but that "we intend to move forward with the implementation of these guidelines…It's really important not to raise unnecessary alarm."

Cook and Ridker had separately identified issues with the calculator last year upon receiving a draft for review from the US National Institutes of Health's National Heart, Lung, and Blood Institute, which was initially developing the guidelines. The researchers indicated at the time that the calculator was not working among the populations they tested using the draft guidelines. Upon release of the final guidelines and risk calculator last week, Cook and Ridker found that the previously identified issues remained.

Donald Lloyd-Jones, co-chairman of the guidelines task force, indicated that the panel may not have received Cook and Ridker's responses. However, he mentioned that the committee was aware that the calculator could overestimate risk in some populations, adding "there's nothing wrong with these equations." Lloyd-Jones suggested that Cook and Ridker's findings may have stemmed from the fact that they used extremely healthy cohorts, while the guidelines used representative cohorts.

For related analysis, read Physician Views: How have cardiologists, internal medicine specialists and general practitioners reacted to the new AHA/ACC cholesterol management guidelines.

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