Diagnosis of pulmonary tuberculosis using Ziehl-Neelsen stain or cold staining techniques?

Acid-fast bacilli microscopy is the first step in the diagnosis and screening of pulmonary tuberculosis (PTB) in developing countries. It remains a rapid and inexpensive diagnostic tool for diagnosing a large number of PTB cases with limited resources.

To evaluate three different staining techniques used in the detection of acid-fast bacilli. The conventional Ziehl-Neelsen (ZN) stain and two cold stains, Gabbett's cold stain and modified cold stain (MCS), were compared with sputum culture.

A total of 300 sputum samples from 100 clinically suspected PTB patients referred to Maamorah Chest Hospital in Alexandria, Egypt, were tested. For staining and culture, three sputum samples from each patient were collected (one 'on spot' and two early morning samples) and pooled together. Smears were prepared using three different staining methods (ZN, Gabbett's cold stain, and MCS) and were inoculated in the Lowenstein-Jensen media.

Comparison of sputum staining results using three different staining techniques versus culture proved that the highest sensitivity and specificity were seen for Gabbett's stain (76.6 and 98.5%, respectively). ZN stain had a sensitivity and specificity of 70 and 97.1%, whereas MCS had a sensitivity and specificity of 60 and 95.7%, respectively.

Gabbett's stain was more accurate in the diagnosis of PTB compared with both ZN and MCS, even though the results were not statistically significant. It can replace ZN for initial diagnosis and follow up of cases. It is also easier, faster, and does not require a heating step.