Prognostic variables for high titres in a fluorescent antibody test to diagnose tuberculosis

The four hospitals and a tuberculosis clinic in the province of Zeeland, The Netherlands.

To assess the usefulness of PPD antibody measurement in the diagnosis of tuberculosis in patients admitted to hospital.

Sixty-one patients presenting with active tuberculosis, and 215 control patients were included in the study. Initial serum PPD antibody titres were determined with a macrophage uptake Fluorescent antibody test (MuFat) to construct a discrimination model between Tuberculosis (TB) and non-TB. We also retrospectively collected clinical parameters of the TB patients at presentation. Univariate and multivariate logistic regression are used to identify variables predicting high antibody titres.

In TB patients, the presence of clinical symptoms (OR=10.63) and the presence of at least two concurrent non-lymph node disease localizations outside thorax and abdomen (OR=13.94) are necessary and sufficient to predict high titres. The logistic model shows a significant contribution of the 2log (titre) to the discrimination between TB and non-TB patients. At a cut-off value of 128, a specificity, sensitivity, and positive predictive and negative predictive values of 97%, 39%, 80% and 85%, respectively, are calculated in the study cohort.

Our data suggest an application of the test at high cut-off values for timely diagnosis of difficult-to-diagnose TB patients. The results of this retrospective study will have to be confirmed in further prospective studies.