Absence of Sex Bias in the Referral of Patients for Cardiac Catheterization

Abstract

It has been suggested that women with clinical evidence of coronary artery disease are less often referred for cardiac catheterization than are men. To determine whether there is sex-related bias in referral for cardiac catheterization, we prospectively studied a cohort of 410 symptomatic outpatients (280 men and 130 women) who were being evaluated with exercise testing for possible coronary artery disease. Before the patients underwent exercise testing, 15 cardiologists from an academic medical center were asked to predict the probability that the patients they saw in the cardiology clinic would have angiographic evidence of any obstructive coronary disease (stenosis of 75 percent or more); the probability of severe coronary disease (three-vessel or left main coronary artery disease); the probability of left main coronary artery disease; and the probability of survival one, three, and five years after the evaluation. Similar predictions were generated by previously validated statistical models with use of data collected before exercise testing from the history, physical examination, and 12-lead electrocardiography with the patient at rest. Overall, women were referred for cardiac catheterization significantly less often than men (18 percent vs. 27 percent, P = 0.03). As compared with men, women had a significantly lower pretest probability of coronary disease (as estimated by their physicians) and a lower rate of positive exercise-test results. After accounting for differences in these two factors, sex was not an independent predictor of referral for catheterization. Comparing physicians' estimates of outcome with those generated by the statistical models revealed no evidence that the physicians were underestimating the risk of coronary disease in women. Furthermore, physicians' predictions did not underestimate the probability of any obstructive coronary disease in men and women who subsequently underwent catheterization. Academic cardiologists made appropriately lower pretest predictions of categories of disease in women with possible coronary artery disease than in men, and these assessments, along with women's lower rate of positive exercise tests, rather than bias based on sex, accounted for the lower rate of catheterization among women. .