Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru.
Int J Tuberc Lung Dis. 2011 Feb;15(2):211-6, i.
Ten peripheral laboratories performing routine acid-fast bacilli (AFB) smear microscopy in Lima, Peru.
To test whether external quality assessment (EQA) rechecking of AFB smears becomes more efficient with stratified lot sampling of treatment follow-up smears.
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.
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.
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.
利马，秘鲁的十个外围实验室常规开展抗酸杆菌（AFB）染色显微镜检查。
检测在常规诊断性涂片阳性率较低的情况下，采用治疗随访涂片的分层批量抽样进行外部质量评估（EQA）复查，是否会更有效率。
连续两年，随机选择和盲法复查 36 张治疗随访载玻片和 24 张诊断性载玻片的分层批量样本。第二个对照员确定有分歧的玻片的最终结果。在监督访问期间，向实验室技术人员提供反馈。
随访玻片中的假阴性错误比疑似肺结核玻片中的更多：25 比 3。这代表在 720 张随访玻片中有 3.5%的漏诊率，而在 480 张诊断性玻片中只有 0.6%。在这两年里，阳性预测值都很高。分别有三个和八个实验室在第一年和第二年没有达到相对敏感度 >65%，并且仅在一个实验室中看到了明显的改善。工作量过大似乎使常规性能的提升变得不可能。
在常规诊断性涂片阳性率较低的情况下，采用治疗随访涂片的分层批量抽样进行 EQA，可非常有效地发现常规工作中表现不佳的实验室。
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