Blinded rechecking of acid-fast bacilli smears by light-emitting diode microscopy

Blinded rechecking of auramine-stained acid-fast bacilli (AFB) sputum smears using fluorescence microscopy (FM), especially FM using light-emitting diode (LED), is not well understood.

To examine the rechecking of auramine-stained sputum smears without restaining within a month using LED FM.

A total of 4799 centrifuged smears of sputum samples were stained by the auramine phenol method and examined using LED FM; 564 systematically selected smears were subjected to blinded rechecking without restaining by controllers. The initial results of the readers were compared to those of the controllers. Discrepancies were resolved by a referee. The quality of LED FM was assessed by the referee using the culture result as gold standard.

Among the rechecked smears, one high false-negative error was made by a reader, while one high false-positive error and 19 high false-negative errors were made by the controllers. The errors were resolved by culture. Smear results for 18 slides were not available due to AFB fading.

AFB colour fading using LED FM, which affected the accurate evaluation of blinded rechecking of AFB smears without restaining within a month, is confirmed in this large study.