The utility of routine screening of patients with uveitis for systemic lupus erythematosus or tuberculosis. A Bayesian analysis
J. T. Rosenbaum and R. Wernick
Department of Medicine, Oregon Health Sciences University, Portland 97201.
The indications for many laboratory tests in patients with uveitis are
controversial. Bayes' theorem allows a mathematical approach to the
assessment of the utility of a laboratory test based on the sensitivity of
the test, the specificity of the test, and the pretest likelihood that the
disease the test is intended to identify is present. We have utilized
Bayes' theorem to assess the utility of routine antinuclear antibody and
purified protein derivative testing in patients with uveitis. Based on
published data about the sensitivity and specificity of each of these
tests, as well as the prevalence of systemic lupus erythematosus and
tuberculosis among patients with uveitis, we calculated that a patient with
uveitis and a positive antinuclear antibody test result has less than a 1%
chance of having systemic lupus erythematosus and that a patient with
uveitis and a positive purified protein derivative test result has a 1%
likelihood of having tuberculosis. These low probabilities mean that
neither test is useful in the routine evaluation of patients with uveitis,
and indiscriminate use may lead to improper diagnosis, increased costs,
and, occasionally, inappropriate therapy.
