title: Quality assessment of smear microscopy by stratified lot sampling of treatment follow-up slides.
abstract: METHODS
  Ten peripheral laboratories performing routine acid-fast bacilli (AFB) smear microscopy in Lima, Peru.
  
  
  OBJECTIVE
  To test whether external quality assessment (EQA) rechecking of AFB smears becomes more efficient with stratified lot sampling of treatment follow-up smears.
  
  
  METHODS
  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.
authors.affiliation: Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru. larissaotero@gmail.com
authors.forename: L
authors.initials: L
authors.lastname: Otero
authors.forename: A
authors.initials: A
authors.lastname: Van Deun
authors.forename: J
authors.initials: J
authors.lastname: Agapito
authors.forename: R
authors.initials: R
authors.lastname: Ugaz
authors.forename: G
authors.initials: G
authors.lastname: Prellwitz
authors.forename: E
authors.initials: E
authors.lastname: Gotuzzo
authors.forename: P
authors.initials: P
authors.lastname: Van der Stuyft
mesh_terms: D000995:Antitubercular Agents / Q000627:therapeutic use; D019411:Clinical Laboratory Techniques / Q000592:standards*; D005188:False Negative Reactions; D005189:False Positive Reactions; D006801:Humans; D008853:Microscopy / Q000592:standards*; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification*; D015588:Observer Variation; D010568:Peru; D017410:Practice Guidelines as Topic; D011237:Predictive Value of Tests; D019984:Quality Indicators, Health Care; D015203:Reproducibility of Results; D016896:Treatment Outcome; D014376:Tuberculosis / Q000175:diagnosis* / Q000188:drug therapy / Q000382:microbiology; D016526:Workload
chemical_list: D000995:Antitubercular Agents