Quality assessment of smear microscopy for acid-fast bacilli in the Argentine tuberculosis laboratory network, 1983-2001.

SETTING

Tuberculosis Laboratory Network, Argentina.

OBJECTIVES

1. To evaluate the technical quality of smear microscopy for acid-fast bacilli (AFB) supervised in 1983-2001, and 2) to analyse the effect of procedural errors on the results.

DESIGN

Registers of technical evaluation results for AFB microscopy were analysed. The quality of specimens, smears, staining and readings were evaluated, as was the relationship between these parameters.

RESULTS

The proportion of good quality specimens was considered acceptable. A direct relationship was demonstrated between positivity in results and mucopurulent sputum. The proportion of thin smears was relatively high. Positivity and bacillary count were lower in thin smears. Staining quality was considered good. The average agreement in readings throughout the country was 98%. Nevertheless, the false-positive rate was considered significant, and 46% of false-positive results were associated with defective staining.

CONCLUSIONS

The technical quality and agreement in the laboratory network were satisfactory. Nevertheless, improvements need to be made in the following: the quality of the smears, staining and reading, coverage, decentralisation of supervision, the slide selection method and data registration. Operational research on the storage and preservation of slides is also necessary.