[Evaluation of the Fluo-RAL (RAL) kit for the identification of mycobacteria by fluorescence microscopy]

Aim of the study: This study has examined the sensitivity of a commercially available fluorochrome stain, the Fluo-RAL kit (RAL), in comparison to the Degommier's stain as gold standard.

Materials and methods: Hundred and thirty-three twin smears, made directly from samples or after their decontamination with N-acetyl-L-cysteine NaOH, were stained, the first slide with the Degommier's method and the second with the Fluo-RAL kit. The samples were 58 sputums, 31 broncho-aspirations, nine gastric lavages, 11 bronchoalveolar lavages, six pleural fluids, two cerebro-spinal fluids, 11 biopsies, two blood cultures and two deep pus. They were examined with 400 × objective under standard fluorescence UV filter by two laboratory technicians independently. The results were expressed with semi-quantitative mean from 0 to 4+.

Results: Hundred and thirty-two results were agreed in grading between the two methods: 73 negative smears, nine quantified as rare (1+), 11 as few (2+), 32 as moderate (3+) and seven as numerous (4+). The only discrepant result had concerned a positive smear quantified as 1+ with the Degommier's stain and as 2+ with the Fluo-RAL kit. This discrepancy was confirmed after a second examination.

Conclusion: After this study, the Fluo-RAL kit was considered as agreed for its daily use in our laboratory. It improves the standardisation of fluorescence microscopy without additional cost or waste of time and reduces the chemical risk in the laboratory. This test, associated with reading using light-emitting diodes, could allow the development of fluorescence microscopy, the higher sensitive method for direct diagnosis of tuberculosis, in poor-resource countries where tuberculosis is a public health problem.