PURPOSE: The objective of the study is to evaluate the usefulness of doing multiple sputum acid fast bacilli (AFB) smears in the diagnosis of pulmonary tuberculosis after the implementation of external quality assurance (EQA) in Directly Observed Therapy Short-course (DOTS) microscopy units.
METHODS: The Philippine Tuberculosis Society, Inc.(PTSI) has an accredited DOTS facility with a certified microscopy unit practicing EQA since April 2004. The laboratory register was reviewed from April 2004 to December 2005. All patients who completed at least three sputum AFB smears for the diagnosis of pulmonary tuberculosis with at least one positive result were included in the study. The frequency of positivity on the first, second, and third specimen and a combination thereof was determined and analyzed.
RESULTS: One hundred seventy four patients were included in the study. One hundred sixty six (88%) patients were considered positive using the NTP definition of two positives out of three or more specimens. Only eight (5%) patients had a single positive out of the first three specimens. Seven of the eight patients were considered positive after another set of three sputum smears were done. One positive out of the first two specimens predicted 98.8% of all true positives with a positive predictive value of 100% and zero false negative. When two positive smears is required for diagnosis, the addition of a third specimen significantly increases detection rate (p=0.000032).
CONCLUSION: A positive sputum smear on at least one of the first two smears is probably enough to label the patient as smear positive and justifies the initiation of anti-Koch’s medication when the quality of sputum microscopy is assured. The collection of a third specimen may only be needed in cases where the first two specimens are negative.
CLINICAL IMPLICATIONS: In a developing country like the Philippines, doing only two AFB smears for the diagnosis of pulmonary tuberculosis instead of three as previously recommended would save precious resources.
DISCLOSURE: Leander Simpao, None.