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

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.