THE IMPORTANCE OF WORK-UP (VERIFICATION) BIAS CORRECTION IN ASSESSINGTHE ACCURACY OF SPECT TL-201 TESTING FOR THE DIAGNOSIS OF CORONARY-ARTERY-DISEASE

Noninvasive testing is often evaluated by the sensitivity and specific ity in comparison with a more invasive, but more definitive ''gold'' s tandard. However, work up or verification bias, which occurs when the results of a noninvasive test impact the decision to perform the gold standard invasive test, increases the ''observed'' sensitivity and dec reases the ''observed'' specificity of the noninvasive test. Most larg e clinical studies utilizing a noninvasive technique to diagnose coron ary artery disease have biases, particularly work up bias. To obtain m ore accurate measurements of sensitivity and specificity, we determine d the observed sensitivity and specificity of stress (exercise and dip yridamole) single photon emission computed tomographic (SPECT) thalliu m testing for the detection of coronary artery disease by angiography, and then applied previously published equations to correct for work-u p bias. From a computerized data base, reports of 4354 stress SPECT th allium studies from January 1, 1986 through December 31, 1992 were rev iewed. All patients with a known history of myocardial infarction or p rior coronary angiography were excluded, leaving 2688 patients. From t his total, 471 patients underwent coronary angiography within 90 days following stress SPECT thallium testing. Coronary artery disease was d efined as a visually assessed stenosis of a coronary artery or a major branch >50%. Of the 2688 stress SPECT thallium studies, 1265 were nor mal and 1423 were abnormal. For the 471 patients who underwent cathete rization within 90 days following stress SPECT thallium testing, the ' 'observed'' sensitivity and specificity were 98 and 14%, respectively. After correction for work up bias, the corrected sensitivity and spec ificity were 82 +/- 6% and 59 +/- 2%, respectively. Most studies utili zing noninvasive technologies for the detection of coronary artery dis ease include patients with known coronary artery disease and have work -up bias as well. By knowing the thallium results of patients with and without catheterization, we were able to correct for work-up bias. Th ese data provide a better estimate of the sensitivity and specificity of stress SPECT thallium testing.