Another important QC is a cross-checking of smear slides examined by one technician by another (laboratory head himself or his deputy) in the same laboratory in a blind fashion. It can be practiced in NRL or intermediate laboratories (IL) which are responsible for QA of the peripheral microscopy centers. In some laboratories QC of positive smear slides is operated by rechecking every slides by another worker in the same laboratory before reporting the results. Negative slides will be rechecked after random sampling by the laboratory head. Plausibility control can also be used for QC of smear microscopy by comparing a frequency distribution of a series of tests with the average values of many series.
3. Proficiency testing
PT can be operated by (1) the quality monitoring during supervisory visit, (2) sending the slides with known contents of AFB to the periphery, and (3) sending slides from periphery to center.
(1) Supervision
Monitoring of smear microscopy quality on supervisory visit is an efficient way because it permits direct contact with peripheral laboratory worker and direct observation of entire laboratory processes. The supervisor can easily identify causes of error if any and motivate the worker. However this approach is labor intensive, expensive and difficult to cover whole country only by NRL. Thus it has to be done by intermediate laboratories or selectively when unsatisfactory performance of a peripheral laboratory has been found on the previous PT. During visit to the peripheral laboratory the supervisor should check workload, facility and equipment for safety practice and works, and stocks of supplies and consumables. Specimen registration, marking on specimen containers and smear slides, storage of smear slides for PT, and recording and reporting of the results should also be carefully reviewed.
The performance evaluation also is an important task of the supervisor. The supervisor reviews the laboratory register to analyze the case-yield rate of smear microscopy and smear positive rate of the follow-up examinations. The case-yield rate is influenced by many factors as though it would fall between 5 and 20% mostly. In general positive smear is encountered in approximately 10% Of follow-up examinations. If these figures are too low, it might resulted from superficial microscopy, poor staining or mis-conduct. Smear preparation is also evaluated by checking the smear size, thickness and cleanness. It is also important to check the maintenance of microscope. A few positive smear slides should be read using their microscope to check its function, staining of AFB and presence of fuchsin crystals. For proficiency testing PL must keep all the smear slides they examined. The supervisor should check whether they keep slides in order and properly as the guideline described and then randomly select the slides for PT.
(2) Proficiency evaluation with smear slides with known result
Under certain setting the proficiency of peripheral laboratory workers can be evaluated with smear slides with known results, which are sent from the reference laboratory. A set of slides with known content of AFB can be collected from the routine works or prepared with heavy bacillary sputum and negative sputum specimens using mucolytic agent, N-acetyl-L-cysteine. This system permits proficiency evaluation of affiliated laboratories with very little efforts and makes easy to implement and to identify serious structural and procedural defects in smear microscopy if any. However it is not possible to evaluate smear preparation and staining if use stained slides and to overcome bias derived from use of unlimited reading time by a peripheral laboratory worker. And it is not designed to evaluate the routine performance.
This type of evaluation system is very useful to assess the proficiency of newly recruited laboratory workers in smear microscopy at the end of training. The slides for this purpose usually consist of 10 negative slides and 5 slides of 1+, 3 slides of 2+, and 2 slides of 3+.
(3) Rechecking of smear slides examined by peripheral laboratory workers
Proficiency evaluation by rechecking smear slides examined by peripheral laboratory worker is most widely practicing QA system. It is rather easy to implement countrywide, permits to evaluate the routine performance of PL, and does not impose workload to periphery. However this type of proficiency evaluation impose heavy workload to the reference laboratory (RL), thus it may lead to inaccurate rechecking unless additional staffing with well trained and experienced workers is followed.
1] Design: (a) The slides are randomly selected by the supervisor on the spot during his or her periodical supervisory visit from the slide boxes where the peripheral worker kept positive and negative smear slides separately and
