Flawed Gauge for Cholesterol Risk Poses a New Challenge for Cardiologists

By GINA KOLATA

New York Times

Published: November 18, 2013

http://www.nytimes.com/2013/11/19/health/flawed-gauge-for-cholesterol-risk-poses-a-new-challenge-for-cardiologists.html?ref=health

Cholesterol Treatment

• This week, cardiologists learned that a new online calculator meant to help them determine a patient’s suitability for cholesterol treatment was flawed, doubling the estimated risk of heart attack or stroke for the average patient.

• But fixing it would not be easy, because it is based on older data, and heart attack and stroke rates today are much lower than in decades past, meaning that people are at less risk than might be expected from historical extrapolations.

Outdated Risk Figures

• Yet the outdated risk figures are the only ones available for researchers to use as assessment tools, cardiologists say, and that raises real problems for the new risk calculator, which the American Heart Association and the American College of Cardiology posted online last week as part of a radical new set of guidelines for treating high cholesterol.

• The guidelines, which are supposed to shape the way doctors prescribe cholesterol-lowering statins, recommend looking beyond a patient’s cholesterol readings.

100% Exaggeration

• Two Harvard researchers, Dr. Paul M. Ridker and Dr. Nancy Cook, revealed that the new calculator released with fanfare last week exaggerated the true risk of a heart attack or stroke by an average of 100 percent. Moreover, they said, the committee that developed the calculator knew that the online tool was inaccurate yet told doctors to use it in deciding whom to treat.

• The data that was used to build the calculator was 20 years old, the researchers said, and a lot has happened since then. Many fewer people have heart attacks and strokes. Those who have them do so at older ages. Women are now nearly as susceptible as men.

Nonlinearity

• But there also is another issue, said Dr. H. Gilbert Welch, a medical professor at Dartmouth. The calculator, like many others used in medicine, is based on a mathematical model that assumes that risk rises in a straight line. As levels of blood pressure rise, for example, the chances of a heart attack or stroke rise in concert, the calculator assumes. In reality, Dr. Welch said, that line is far from straight.

• “The model suggests that lowering systolic blood pressure from 130 to 100 is nearly as important as from 180 to 150,” he said. “I doubt there is a cardiologist in the country that believes that.”

• http://www.diffen.com/difference/Systolic_vs_Diastolic_Blood_Pressure - Good definitions

Old Data

• If data are old, they may miss a lot of improvements.

• But what if other factors have changed? Diet, exercise, …?

• Any particular risk factor may OVERESTIMATE the risk.

Risk

Risk Factor0

Linearity

• I’m guessing that the proper relationship should be S-shaped.

• Not linear.• Look at marginal effects.

Risk

Systolic

0

1

60 120 180