Comparative Analysis of Performance of PREVI Fluo TB Method by Using LED-Microscopy

Abstract

There is a need for rapid, practical and accurate tuberculosis diagnostic tools that are adapted to resource-poor settings in order to ensure that those affected receive proper and timely treatment. Light-Emitting-Diode microscopy (LED) has recently been endorsed by the WHO for diagnosis of TB in these countries. A much recent smear diagnosis method, PREVI Fluo TB by using LED microscopy, has been made available. However, due to the novelty of the method, there is no information available on the specificity and sensitivity when compared to established methods such as the ordinary LED-Auramine O or the classical widely used Ziehl- Neelsen (ZN) in TB positive persons. This study was undertaken to compare the sensitivity, specificity, positive predictive value and negative predictive value of PREVI Fluo TB stain with ZN method and Auramine O-LED microscopy taking culture as reference. A prospective cross sectional study was conducted in St. Paul’s Hospital Millennium Medical College, Addis Ababa, Ethiopia. Spot- Morning-Spot sputum samples from 248 TB suspected study participants were collected. The smear detection rate of PREVI Fluo TB, ZN, Auramine O and culture were found to be 35 (14.1%), 24(9.7%), 44(17.7%) and 30(12.1%) respectively. The sensitivity of the PREVI Fluo TB method was 76.67%, better than ZN and slightly less than Auramine O which were 59.07% and 78.13% respectively. Nevertheless, the specificity (94.5%) was lower than ZN (96.79%) and higher than Auramine O (91.2%). The negative likelihood ratio of PREVI Fluo TB, ZN, and Auramine O methods were 0.25, 0.45, and 0.24 respectively. The PREVI Fluo TB method had a PPV of 65.71% which is higher than the Auramine O (56.82%) but with a comparable NPV (96.71% and 96.57% respectively). The respective agreements of the ZN, Auramine O and PREVI Fluo TB methods with the gold standard were K=0.585, K=0.621 and K=0.664. There was a substantial agreement of PREVI Fluo TB result with ZN (k=0.636) and Auramine O methods (K=0.745).Given the practical benefits of PREVI Fluo TB for TB diagnosis, and comparable accuracy to the current standard of Auramine O fluorescence method and the gold standard culture, PREVI Fluo TB should be considered by TB diagnostic laboratories, as an alternative diagnostic tool for conventional Auramine O fluorescent stain.