An evaluation study of the sputum smear concentration technique for the laboratory diagnosis of pulmonary tuberculosis

Abstract

The microbial diagnosis of Pulmonary Tuberculosis plays a key role in routine treatment and Tuberculosis control Programmes in developing countries. Many patients have presented with signs and symptoms of pulmonary tuberculosis, of which consecutive direct sputum smear microscopy have given negative results for Acid-Fast Bacilli (AFB). Microscopy of smears made directly from sputum has a low sensitivity and there is an urgent need for improved methods. This study was carried out at the Yaoundé University Teaching Hospital and is aimed at evaluating the sputum smear concentration technique in the laboratory diagnosis of pulmonary TB. Sputum samples were collected in screw-cap tight containers and evaluated by both the direct and concentrated methods. Microscopy of direct smears of sputum after liquefaction with 5% sodium hypochlorite (NaOCl) solution; and concentration of the organisms by centrifugation were compared and evaluated. Results showed an increase in sensitivity from 18.27% to 25% with a specificity of 90.95%. The tuberculosis prevalence was 25%. 13.33% belongs to the age range 20-40 years and 11.67% to the age range >40 years. The positive predictive value was 73%. We concluded that the use of sodium hypochlorite (NaOCl) in the concentration of acid-fast bacilli (AFB) in sputum significantly improves the laboratory diagnosis of pulmonary tuberculosis.

Keywords: Sputum smear concentration, Laboratory diagnosis, Pulmonary tuberculosis