Quality of sputum smear microscopy in Taiwan

Four mycobacteriology laboratories in northern Taiwan collected slides from their routine work for an international training course on quality assurance of sputum smear microscopy held from 19-27 August 2004 in Taipei. Rechecking of a random sample of these slides provided an opportunity to evaluate the quality of sputum smear microscopy in the collaborating laboratories.

Participants used a systematic sampling method to choose 100 to 120 slides from a set of 600 to 800 slides for evaluating the quality of smear and rechecking. Recheckers were blinded to the microscopy results reported by the testing laboratories. Discordant slides were re-examined by a second rechecker in order to make the final decision.

A total of 433 slides were evaluated for smear quality. Of these 433 slides, 177 (41%) had proper smear size, 194 (45%) proper thickness and 212 (49%) proper staining. Rechecking of slides revealed that 2 of 4 laboratories had at least 1 high false-negative and 3 of 4 laboratories had at least 1 low false-negative result.

We conclude that: 1) the 2 laboratories with high false-negative results need a supervisory visit in order to determine the causes; and 2) the national tuberculosis program should direct more attention to the quality of sputum smear microscopy and develop a formal plan for external quality assessment of sputum smear microscopy in Taiwan.