Quality assessment of smear microscopy by stratified lot sampling of treatment follow-up slides

L Otero, A Van Deun, J Agapito, R Ugaz, G Prellwitz, E Gotuzzo, P Van der Stuyft

    Research output: Contribution to journalA1: Web of Science-articlepeer-review


    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 languageEnglish
    JournalInternational Journal of Tuberculosis and Lung Disease
    Issue number2
    Pages (from-to)211-216
    Number of pages6
    Publication statusPublished - 2011


    • 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


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