If you can’t trust a heart attack risk assessment that can be done with a few clicks of the mouse, what can you trust?

New research suggests that a Web-based tool used to calculate the risk of heart attack over a 10-year period is faulty, misclassifying 15% of patients who use it—or nearly six million people. Determining this type of risk, it seems, may not be that so simple.

According to a study published in the Journal of General Internal Medicine, the American Heart Association’s Heart Attack Risk Calculator, a “simplified version of the Framingham model,” is less reliable than the original test. Perhaps most notable is that the fact almost four million Americans who used the point-based tool were “inappropriately shifted into higher-risk groups that are more likely to be treated with medication.”

These findings, said the study’s lead author, William J. Gordon of Weill Cornell Medical College in New York, have “significant implications” for clinical care.

Gordon and colleagues sought to compare future coronary risk estimates and risk group classification generated by the original, complex Framingham model and the simplified, point-based version. The researchers assessed 2,543 patients between the ages of 20 and 79 from the 2001—2006 National Health and Nutrition Examination Surveys (NHANES) for whom Adult Treatment Panel III (ATP-III) guidelines recommended formal risk stratification. They calculated the 10-year risk of major coronary events for each patient using the original and point-based Framingham models, and then compared discrepancies in risk estimates and determined whether these differences would place subjects into different ATP-III risk groups (<10% risk, 10–20% risk, or >20% risk).

Of the 39 million eligible adults, the original Framingham model categorized 71% of subjects as having “moderate” risk (<10% risk of a major coronary event in the next 10 years), 22% as having “moderately high” (10—20%) risk, and 7% as having “high” (>20%) risk, according to Gordon and colleagues, who found that “estimates of coronary risk by the original and point-based models often differed substantially.”

The Heart Attack Risk Calculator classified 15% of adults (5.7 million people) into different risk groups than the original model, with 10% (3.9 million people) miscategorized into higher risk groups and 5% (1.8 million people) into lower risk groups, “for a net impact of classifying 2.1 million adults into higher risk groups. These risk group misclassifications would impact guideline-recommended drug treatment.

The web-based tool works by asking patients a series of questions and, based on those answers, calculating the risk for future coronary events. The questions focused on gender, age, smoking habits, family history of early heart disease, history of any atherosclerotic heart or blood vessel disease events, conditions, or procedures (such transient ischemic attack, coronary artery bypass graft, or surgery for a circulation problem), history of diabetes, height, weight, waist measurement, systolic and diastolic blood pressure, and cholesterol and triglyceride levels. Those who answer all of the questions are then given a percentage indicate the future risk of heart attack, and told what steps they can take to lower their risk. Patients can print out the report and bring it to their physician.

According to an article published in the New York Times, the first version of the calculator used a complicated mathematical formula that was developed over several decades through the Framingham Heart Study, which was conducted by the National Heart, Lung and Blood Institute and Boston University. This version, it said, is “equally user-friendly” compared with the newer tool, and is “significantly more reliable.”

In the article, Michael Steinman, MD, of San Francisco Veterans Affairs Medical Center and the University of California, San Francisco was quoted as saying that “People were told that for clinical purposes either one of the formulas could be used, that they were interchangeable.” However, “Our study highlights that there can be meaningful differences for individual patients.”

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