External quality assessment for acid fast bacilli smear microscopy in eastern part of Ethiopia

Desalegn Admassu Ayana, Zelalem Teklemariam Kidanemariam, Habtamu Mitiku Tesfaye, Fitsum Weldegebreal Milashu

External quality assessment (EQA) of sputum smear microscopy is essential and indispensable component of any tuberculosis program. This study assessed the EQA of acid fast bacilli (AFB) smear microscopy through onsite evaluation, blinded rechecking and panel test. A one year study was conducted on eight health institution laboratories from December 2011 to December 2012. Onsite evaluation, blinded rechecking and panel tests were used to collect data. Data were analyzed using SPSS version 16. Sensitivity, specificity, predictive values, and proportions of false readings were calculated. The level of agreement was measured using Kappa (κ) value. Problems observed during onsite evaluation include shortages of materials, disinfectant, and poor storage and working condition. A total of 578 slides were collected for blinded rechecking, of which 102 (17.6 %) were reported as positive by peripheral laboratories. The panel test revealed an overall error of 17 (25.25 %) of which 14 (17.5 %) were minor errors [low false negative 6 (7.5 %) and low false positive 8 (10 %)], and 3 (3.75 %) were major errors (high false positive). The sensitivity, specificity, positive predictive values (PPV) and negative predictive values (NPV) of the peripheral laboratories were 83.5, 97.8, 91.7, and 95.7, respectively. The false readings at the peripheral laboratories were 32 (5.5 %). Agreement on reading the slides was observed on 546 (94.5 %) slides (K = 0.84, SE = 0.054). Lack of reagents, supplies, favorable working environment and AFB related technical problems were identified in the peripheral laboratories. High false negative error was found to be the predominant major error. A continuous and strong EQA scheme should be implemented to avoid reporting errors and produce quality sputum results.