Evaluating rapid tests for streptococcal pharyngitis: the apparent accuracy of a diagnostic test when there are errors in the standard of comparison.

The evaluation of new rapid antigen detection tests for streptococcal pharyngitis is complicated by the presence of errors in the standard of comparison. Even "gold standard" throat cultures are not perfectly accurate. This article is an analysis of how errors in the comparison cultures affect the apparent accuracy of new tests for streptococcal pharyngitis. One of the questions addressed is whether throat cultures performed in a physician's office are accurate enough to use as a standard in a clinical trial of a new rapid test. While the accuracy of office cultures is accepted by many to be adequate for diagnostic purposes, this analysis shows that when evaluating a new test stricter conditions must be placed on the accuracy of the cultures used for comparison.