Light-emitting diode with various sputum smear preparation techniques to diagnose tuberculosis

Mawenzi Regional Hospital, northern Tanzania.

To determine the value of light-emitting diode (LED) microscopy in diagnosing tuberculosis (TB) on bleach-treated and direct sputum smears.

Sputum samples were collected from patients suspected of pulmonary TB who presented consecutively at the laboratory for smear evaluation between December 2009 and February 2010. Four smears were prepared from each specimen: conventional Ziehl-Neelsen (ZN), direct auramine, bleach centrifugation and bleach short sedimentation auramine smears. A light microscope was used to examine ZN smears and an LED fluorescent microscope to examine auramine-stained smears.

Of the 267 sputum samples examined, respectively 78 (29%), 62 (23%), 74 (28%) and 48 (18%) were acid-fast bacilli (AFB) positive by the bleach centrifugation, bleach short sedimentation, direct auramine and ZN methods. Bleach centrifugation identified 30 (11%) more positives than ZN microscopy (P < 0.001), but was not superior to the direct auramine method (P = 0.46), which yielded 26 (10%) more positives than ZN microscopy (P < 0.001). Fluorescent LED required a shorter smear reading time (1.5 min on average), while the light microscope took 4 min (P < 0.001).

Fluorescent LED microscopy with direct smear preparation is rapid and effective. Further studies are needed to ascertain its performance under routine conditions.