Letter to the editor

LETTER TO THE EDITOR

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the Editor:

In a recent publication in the Journal, Johansen etreported on the sensitivity and specificity of myocar-perfusion imaging (MPI) for detection of coronary

ry disease in a study population without post-testrral bias. The effect of post-test referral (verification)has been well documented, and statistical methods

djust for it have been reported.2 Using an Internet-ed tool, we have offered the potential to correct forrral bias if the referral rates for positive and negatives are known.3

We have performed an additional analysis to theprovided by Johansen et al.1 On the basis of the

bers provided, we calculated that the true-positive,e-positive, true-negative, and false-negative findingsheir study were 94, 48, 183, and 32, respectively. Ifstarts from the result of the MPI stress test, assumesrral rates for angiography of 30% for positive testlts and 5% for negative test results, similar to those

viously reported in the literature, and uses the toolwe have developed,3 the result is an apparent

sitivity of 93% and apparent specificity of 38%. Bothhese values are very similar to those reported in otheries assessing the sensitivity and specificity of MPIdiagnosis of coronary artery disease that Johansen etuote in their article.1 Therefore post-test referral biasy explains the difference that the authors comment on

een the results reported by themselves and previousilar studies that were subject to referral bias.

This post hoc adjustment also provides additionalport for the authors’ statement that there is only all likelihood to have non–MPI-related post-test refer-bias in their study and demonstrates that the possi-ty of a significant effect of such biases on the reportedlts is likely small.

nowledgment

The author has indicated he has no financial conflicts ofrest.

Peter G. Danias, MD, PhDHygeia Hospital

Maroussi, GreeceTufts University School of Medicine

Boston, Mass

erences

ohansen A, Høilund-Carlsen PF, Christensen HW, Vach W, Jør-ensen HB, Veje A, et al. Diagnostic accuracy of myocardialerfusion imaging in a study population without post-test referralias. J Nucl Cardiol 2005;12:530-7.egg CB, Greenes RA. Assessment of diagnostic tests when diseaseerification is subject to selection bias. Biometrics 1983;39:207-15.anias PG, Parker JA. Novel Internet-based tool for correcting

pparent sensitivity and specificity of diagnostic tests to adjust foreferral (verification) bias. Radiographics 2002;22:e4.

doi:10.1016/j.nuclcard.2005.12.007