Comparative Analysis of Performance of PREVI Fluo TB Method by Using LED-Microscopy in TB Suspected Patients at St. Paul’s Hospital Millennium Medical College, Addis Ababa, Ethiopia
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Date
2012-06
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Addis Ababa University
Abstract
Background: Tuberculosis is a prominent problem in developing countries. Hence, there is a need for rapid, practical and accurate 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 and TB-HIV co-infected persons.
Objective: The study was undertaken to compare the sensitivity, specificity, PPV and NPV of PREVI Fluo TB stain with ZN method and Auramine O- LED microscopy. Methods: A prospective cross sectional study was conducted in St. Paul‟s Millennium Medical College, Addis Ababa, Ethiopia from October/ 2011-April/2012. Spot-Morning Spot sputum samples from 248 TB suspected study participants were collected. A total of 2,232 slides were made of which 744 slides were subject to be stained by each method. Confirmation was made by Lowenstein-Jenssen (LJ) culture which was used as a reference standard.
Results: 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).
Conclusion: The PREVI Fluo TB fluorescent staining method had nearly identical sensitivity compared to the conventional Auramine O and significantly higher sensitivity than ZN staining method. 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.
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Keywords
Tuberculosis, ZN, Auramine O, PREVI Fluo TB