over 30℃ and relative humidity of over 70%, fuchsin stains of AFB fade out rapidly so that the 2nd and 3rd readers are unable to see them on rechecking. For this reason it is recommendable to restain all the smear slides prior to rechecking in the tropical countries or in hot and humid season. However there is very slim chance that the 2nd reader reports false positive if the smear has been contaminated with environmental mycobacteria in a rinsing water during staining at PL. The rechecking results are recorded in the Form 2 accompanying the slides and hand it over to the supervisor or TB coordinator.
The supervisor or TB coordinator transcribes the 2nd reader's results in the Form 1 and reviews the independent reading results of PL microscopist and RL microscopist. If there are any discrepancies, they have to be read again by another microscopist (3rd reader) in RL without knowing the results of the previous readings. Final results will be based on the third reading.
5] Analysis of slide-checking results: The supervisor or TB coordinator should feed-back the results soon after completion of analysis of the slide rechecking results. Analysis should be made on (a) over-all agreement, (b) false negative rate, (c) false positive rate, and (d) poorly prepared smears. Quantification error is not so important although it permits distinguish very good microscopist from good microscopist.(Table 2)
The supervisor or TB coordinator complete Form 3 and disseminate it not only to all the participating microscopy centers but to the Regional and Central TB Control Offices.
4. Quality improvement
In order to identify error or weakness in laboratory services, a continuous monitoring of performance by PT (and QC) should be made and supervision of technical specialist must be followed immediately if PL showed an unacceptable proficiency. The slide-checking results will let supervisor or TB coordinator to know which PL needs a review of its operation and who needs a corrective training or on the job training. If over-all false readings do not exceed 5%, no special action is necessary to be taken because feed-back of the results will arouse attention. If the false reading rate exceed 5% or more, immediate supervisory visit should be followed and, if necessary, remedial action must be taken to permanently remove defects or weakness in laboratory performance.
False negative cases, if they are new cases and left untreated, should be taken immediately the commencement of treatment and, if they are under treatment, an appropriate case-management action should be taken. The action for false positive cases must be taken with an extreme care only by medical doctor taking account of clinical symptoms and/or radiographic findings because there is possibility to miss by the second and third readers if the selected slides had a very few bacilli and kept poorly.
It is important that supervisory visit to PL also aims at strengthening links and collaboration between diagnostic laboratory services and local program management. If there are serious deficiencies in the way that the laboratory register is kept, remedial action would include retraining of personnel in the administrative aspects of diagnostic services. If a large proportion of single negative smears is detected (as opposed to the required three examinations) remedial action would include discussion with clinical health care workers in charge of attending to patients with respiratory symptoms. Supervision is also useful in detecting problems in the supply of laboratory reagents and materials.
