RESUMEN
SETTING: Laboratories in Mexico that support the national tuberculosis (TB) control program have been involved in an acid-fast bacilli (AFB) microscopy external quality assurance program which includes rechecking 100% of smears identified as AFB-positive by the local laboratories and 10% of smears identified as AFB-negative. Very few errors have been detected in Mexico using non-random selection and unblinded rechecking of the slides. OBJECTIVE: To evaluate the results from a 1-year pilot program involving blinded rechecking of randomly selected AFB slides from local TB laboratories in two Mexican states and determine its feasibility for future implementation. DESIGN: To reduce potential bias, laboratory staff from the National TB Laboratory, Institute for Epidemiological Diagnosis and Reference (InDRE), performed quarterly statistical sampling of AFB smears and on-site evaluations in local laboratories in each state. AFB smears were rechecked at the respective state laboratories with discordant results resolved at InDRE. RESULTS: A significantly greater percentage of errors was detected on the randomly selected, blinded AFB smears than on the non-randomly selected, unblinded smears. CONCLUSION: Random blinded rechecking provides more accurate estimates of AFB microscopy results, resulting in improved diagnosis and monitoring of treatment response.
Asunto(s)
Técnicas Bacteriológicas/normas , Mycobacterium tuberculosis/aislamiento & purificación , Guías de Práctica Clínica como Asunto/normas , Garantía de la Calidad de Atención de Salud , Esputo/microbiología , Tuberculosis Pulmonar/microbiología , Técnicas Bacteriológicas/métodos , Competencia Clínica , Humanos , Técnicas In Vitro , México , Microscopía/métodos , Microscopía/normas , Proyectos Piloto , Esputo/citología , Análisis de Sistemas , Tuberculosis Pulmonar/patologíaRESUMEN
SETTING: In developing countries, tuberculosis is diagnosed by identification of acid-fast bacilli (AFB) on sputum smears. OBJECTIVE: To evaluate the quality of AFB microscopy, the Mexican Secretary of Health National Reference Laboratory implemented proficiency testing for its network of 637 laboratories. DESIGN: A total of 586 (92%) laboratories were inspected and 430 technicians evaluated by proficiency testing consisting of 10 slides with known numbers of AFB. Results were compared with those of slide rechecking and with proficiency testing performed 2 years later. RESULTS: Of the 430 technicians evaluated by proficiency testing in 1998, 196 (46%) scored less than 80% and received intensive training in 1999. From a previous mean score of 65% their results increased to 90% (P < 0.0001). In 2001, they again underwent proficiency testing, and the mean score was 83%. The main factors affecting proficiency testing results were the type of laboratory in which the microscopists worked and the number of low-positive slides (1-9/100) in the test. Laboratories whose work was rechecked had better scores (P = 0.002). Proficiency testing scores and the estimated sensitivity of the microscopist's laboratory were associated (P = 0.01). CONCLUSION: External quality assessment and training improve diagnostic performance. Rechecking and proficiency testing are both viable measures of laboratory performance.