False Negativity of Ziehl-Neelsen Smear Microscopy: Is the Scale-up the Worth It in Developing Countries?

Abstract

Objective: To evaluate the false negative results of Ziehl-Neelsen (ZN) smear microscopy.

Study design: Descriptive study.

Place and duration of study: Mycobacteriology Laboratory, Allama Iqbal Medical College (AIMC) and Jinnah Hospital, Lahore (JHL), Pakistan, from February 2014 to August 2016.

Methodology: A total of 3,951 (pulmonary 2,773 and extra-pulmonary 1,178) samples were collected from strong TB suspected patients attending JHL Lahore. Follow-up cases were excluded. Every specimen was processed for ZN smear microscopy, Lowenstein Jensen (LJ) culture. SPSS 21.0 was used; false negative and positive results of ZN smear were calculated keeping LJ culture as gold standard.

Results: Out of total 3,951 samples, sputum was most frequently found pulmonary sample 48.4% (n=1915), extra- pulmonary samples, pleural fluid and pus samples were most commonly observed samples 12.0% (n=476) and 8.3% (n=329), respectively. Overall false negativity was 23.1% (pulmonary=19.6%, extra-pulmonary=29.2%) (p<0.001), Maximum false negative results were observed in pericardial, synovial, pleural fluids, and pus samples as 40.0%, 38.0%, 33.0% and 32.0%, respectively.

Conclusion: ZN smear microscopy is not a very efficient tool in case of patients with the low mycobacterial load. Therefore, National TB Control programs should consider extending their diagnostic approaches from ZN microscopy to more advanced techniques.