Abstract
SETTING: Ten peripheral laboratories performing routine acid-fast bacilli (AFB) smear microscopy in Lima, Peru. OBJECTIVES: To test whether external quality assessment (EQA) rechecking of AFB smears becomes more efficient with stratified lot sampling of treatment follow-up smears. DESIGN: In 2 consecutive years, a stratified lot sample of 36 treatment follow-up slides and 24 diagnostic slides were randomly selected and blindly rechecked. A second controller determined the final result for discordant slides. Feedback was provided to laboratory technicians during supervisory visits. RESULTS: More false-negative errors were found in the follow-up slides than in the tuberculosis suspect slides: 25 vs. 3. This represented a yield of 3.5% in 720 follow-up slides and only 0.6% in 480 diagnostic slides. Positive predictive values were high in both years. Respectively three and eight laboratories did not reach a relative sensitivity of >65% during the first and second year, and a clear improvement was seen in only one laboratory. Excessive workload seemed to preclude raising the level of routine performance. CONCLUSIONS: EQA with stratified lot sampling of treatment follow-up slides proved very efficient and effective for identifying laboratories with substandard performance in a setting with low positivity rates in routine diagnostic smears.
Original language | English |
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Journal | International Journal of Tuberculosis and Lung Disease |
Volume | 15 |
Issue number | 2 |
Pages (from-to) | 211-216 |
Number of pages | 6 |
ISSN | 1027-3719 |
Publication status | Published - 2011 |
Keywords
- B780-tropical-medicine
- Bacterial diseases
- Tuberculosis
- Mycobacterium tuberculosis
- Diagnostics
- Quality assessment
- Quality control
- Performance
- Sputum smear microscopy
- Sampling
- Follow-up
- False-negative
- Predictive value
- Sensitivity
- Laboratory techniques and procedures