[Clinical evaluation of acid-fast smear examination with light emitting diode fluorescent microscopy]

Fluorescent smear microscopy is one of the recommended methods to detect highly infectious tuberculosis (TB) patients. Recently, fluorescent microscopy using a light emitting diode (LED) as a light source has been developed and introduced. The objective of this study is to evaluate the efficiency of LED fluorescent microscopy.

The clinical specimens were collected from TB suspects and follow-up patients of mycobacteriosis in Double Barred Cross Hospital through Sept. to Oct. in 2008. The specimens were subjected to the ordinary decontamination/concentration process, and the sediments were smeared and stained with auramine O. The slides were examined using an ordinary mercury vapour lamp and a LED fluorescent microscope by at least two laboratory technologists independently. If there was a discrepancy between the first and second reader, the third reader (umpire) judged the result. The treated specimens were also cultured using BACTEC MGIT or 2% Kudoh medium. The smear and culture results were compared with the results of LED fluorescent microscopy.

A total of 1324 specimens, including 1192 sputa and 23 pleural fluid, were collected from TB suspects and patients. The overall agreement, smear positive versus smear negative, occurred in 1,300 of 1,324 specimens (98.2%). Among the mutually positive readings, the agreement on grading was 256 out of 334 (76.6%), and disagreement beyond two grades was observed only in 3 specimens. The smear positive/culture positive rates were not statistically different between two smear methods.

The overall efficiency of LED fluorescent microscopy was similar to that of ordinary fluorescent microscopy with a mercury vapour lamp. The LED costs less than mercury vapour lamp, and has a usable life of more than 40,000 h. It does not require either a dark room for observation, or a long waiting time for stabilization. It was expected that the LED fluorescent microscopy would be utilized widely for the efficient detection of acid-fast bacilli in clinical practices.