Modified cytospin slide microscopy method for rapid diagnosis of smear-negative pulmonary tuberculosis

To evaluate a modified method of the Ziehl-Neelsen stain and determine whether it improves the detection rate of acid-fast bacilli (AFB) in bronchoalveolar lavage fluid (BALF) specimens.

Bronchoscopy of patients with suspected smear-negative pulmonary tuberculosis (PTB) patients was conducted to collect BALF to assess the efficacy and accuracy of the modified method for PTB diagnosis.

A total of 106 BALF specimens was collected from 74 PTB patients on the basis of BALF samples that were culture-positive for Mycobacterium tuberculosis. When analysed by patient, the sensitivity and specificity of our modified method were respectively 87.8% and 99.6%, while the positive predictive (PPV) and negative predictive values (NPV) were respectively 98.5% and 96.8%. Conversely, the sensitivity of direct smears and concentrated smears was respectively 16.2% and 37.8%, with 100% specificity. On analysing 106 samples, the culture positivity rate of the direct smear and the concentrated smear methods was respectively 76.4%, 13.2% and 34%, while it was 91.5% for the modified method.

The sensitivity of our modified method was significantly higher than that of direct or concentrated smears. Overall, the modified method improved the detection rate of AFB in BALF specimens, and provided an efficient and accurate diagnosis of PTB in patients with suspected smear-negative PTB.