Can Fine Needle Aspiration Cytology be Used as a “Proxy Gold Standard” to Diagnose Tuberculous Mastitis?

OBJECTIVE: To assess the performance of fine needle aspiration cytology (FNAC) in the diagnosis of tuberculosis mastitis. MATERIALS AND METHODS: Diagnostic test performance evaluation using two methods—as compared to an alloyed gold standard as well as in the absence of a gold standard. Alloyed gold standard combined the results of acid fast bacilli in cytology smears, histopathological confirmation, and response to treatment. Bayesian estimation of test parameters was done in the absence of the gold standard. RESULTS: FNAC was carried out in 6,496 consecutive cases of breast lump and 104 cases of granulomatous mastitis were detected. Both methods of test parameter estimation identified a high specificity of FNAC for the diagnosis of tuberculosis mastitis (98.9% and 98.4%, respectively). Estimation of sensitivity was falsely high (100%) using the alloyed gold standard because of a workup bias and falsely low (8.41%) using the Bayesian estimation because of low prevalence. Likelihood ratios by both methods suggested that FNAC has good discriminatory capability. CONCLUSION: In situations where prevalence of tuberculosis is high and where facilities for histopathological evaluation do not exist, FNAC can offer an optional alternative to base the therapeutic decision for starting antitubercular treatment.