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Biomédica

Print version ISSN 0120-4157

Abstract

IMAZ, María  and  GROUP OF IMPLEMENTATION OF FLUORESCENCE MICROSCOPY et al. Performance of LED fluorescence microscopy for the detection of acid-fast bacilli from respiratory samples in peripheral laboratories in Argentina. Biomédica [online]. 2017, vol.37, n.2, pp.164-174. ISSN 0120-4157.  http://dx.doi.org/10.7705/biomedica.v37i2.3276.

Introduction:

Light-emitting diode fluorescence microscopy (LED-FM) has been endorsed by the World Health Organization (WHO) for tuberculosis diagnosis, but its accuracy in HIV-infected patients remains controversial, and only some few studies have explored procedural factors that may affect its performance.

Objective:

To evaluate the performance of LED-FM for tuberculosis diagnosis in patients with and without HIV infection using a newer, less expensive LED lamp.

Materials and methods:

We compared the performance of LED-FM and Ziehl-Neelsen (ZN) microscopy on respiratory specimen smears from tuberculosis (TB) suspects and patients on treatment examined by different technicians blinded for HIV-status and for the result of the comparative test. We analyzed the effect of concentrating specimens prior to microscopy using different examination schemes and user-appraisal of the LED device.

Results:

Of the 6,968 diagnostic specimens collected, 869 (12.5%) had positive Mycobacterium tuberculosis cultures. LED-FM was 11.4% more sensitive than ZN (p<0.01). Among HIV-positive TB patients, sensitivity differences between LED-FM and ZN (20.6%) doubled the figure obtained in HIV-negative patients or in those with unknown HIV status (9.3%). After stratifying by direct and concentrated slides, the superiority of LED-FM remained. High specificity values were obtained both with LED-FM (99.9%) and ZN (99.9%).The second reading of a sample of slides showed a significantly higher positive detection yield using 200x magnification (49.4 %) than 400x magnification (33.8%) (p<0.05). The LED-device had a very good acceptance among the technicians.

Conclusion:

LED-FM better performance compared with ZN in HIV-infected patients and user-appraisal support the rapid roll-out of LED-FM. Screening at 200x magnification was essential to achieve LED-FM increased sensitivity.

Keywords : Tuberculosis; fluorescence; microscopy; diagnosis; sputum; acid-fast bacilli.

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