In a patient with a chest pain syndrome, the sine qua non of decision making is an accurate determination of whether coronary artery disease is present and, if so, whether medical therapy or revascularization will yield the best outcome. I have previously argued that noninvasive testing has significant limitations [1]. However, I question whether the study by Christian and colleagues [2] helps clarify the role of exercise thallium stress testing or makes throwing out the baby with the bath water acceptable. I suspect that referral bias explains their findings. In their study, most patients who had an exercise thallium test during the same time period apparently did not require catheterization within 6 months. The odds of having a catheterization if the thallium results were abnormal as opposed to normal was 4:1. The authors' acknowledgment of this limitation unfortunately fails to remedy the problem. Further, What was the sequence of testing for those patients included in the study, that is, those selected for having had both a catheterization and exercise thallium test? It seems that an abnormal thallium result generally led to catheterization. For the remaining patients, how often did uncertainty about the significance of the angiographic disease result in exercise thallium testing? As noted in the article, revascularization was done in 59% of patients classified as high risk and in 23% classified as low risk; this result argues strongly that the exercise thallium results were a significant factor in selecting therapy.

Thus, the reader is left with a dilemma. To apply the results of this retrospective prospective study, one must first select—using exercise thallium testing—those patients who need catheterization (generally those with a positive thallium result) and with the combined results determine in some undefined manner which patients require revascularization. This is not incremental testing and cannot be used to prospectively guide its application.