patients and of probably resistant clinical isolates from patients treated with the corresponding drug for more than nine (or six) months.
?. QUALITY CONTROL (QC) OF SMEAR MICROSCOPY
A. Purpose
The smear microscopy is an utmost important measure to diagnose TB patients, who spread infection in the community and to monitor patient's response to chemotherapy. To achieve the highest possible level of sensitivity and specificity, it is essential to set up the permanent quality control system for smear microscopy for accuracy and reproducibility. A minor technical deviation or faults may lead to an inaccurate results that can be prevented only if a regular checks are applied to everything used and done in the laboratory and to every results obtained. However it is not easy to set up a feasible QC measure for smear microscopy within acceptable efficiency.
B. Organization
QC should be implemented by the higher level laboratories. The NRL cannot cover whole country, thus the intermediate laboratories should practice QC of the peripheral laboratory performances. If TB laboratory services are not well organized yet, then NTP director together with regional or provincial TB coordinator can select some of the peripheral laboratories for QC of the other laboratories.
C. Quality control system
QC can be operated by both internal and external ways. Internal QC is operated by cross-checking smear slides examined by one technician by another (laboratory head himself or his deputy) in the same laboratory either by blinded or by unblinded fashion. It can be practiced in NRL or intermediate laboratories (IL) which are responsible for QC of the peripheral microscopy centers.
External QC, however, is most widely practicing system and operated either (1) by rereading (checking) the smear slides carefully selected from those examined by the peripheral laboratory workers or (2) by evaluating smear microscopy proficiency of peripheral workers with a set of stained or unstained smear slides with known contents of AFB. In the latter system, the smear slides sent by central or intermediate reference laboratories are examined by the peripheral laboratories and the results are reported back to the reference laboratory. The reference laboratory would analyze the reported results and feedback to the participating laboratories. This approach is also often used to assess the proficiency of laboratory trainee at the end of course.
Most of the countries, however, practice QC of smear microscopy by the slides-checking method: (1) the slides can be selected from those examined at the peripheral laboratories and transported to higher level laboratory. All the smear slides should be transported along with a list where the slides markings and microscopy results are clearly indicated and conform to the laboratory registry (or logbook). (2) or the slides can be selected by the supervisor on the spot during his or her periodical supervisory visit from the slides boxes where the peripheral microscopists kept smear positive and negative slides separately after examination.
D. QC by blinded slide-checking
(1) Design
The smear slides examined at the peripheral microscopy centers (PMC) are to be selected randomly by the regional or provincial TB coordinator (or supervisor) from the slides boxes where PMC microscopists kept smear slides after examination or sent to either TB coordinator or higher level laboratory (or QC center). TB coordinator makes a list of smear slides selected and given them to QC center microscopist (or higher level laboratory) without the results of the 1st reader. If any discrepancy is found when compared the results of 1st and 2nd readers. TB coordinator ask another microscopist at QC center to read it and then analyze and feed-back the final results.
QC could be practiced twice in a year or maximum quarterly if it has been confirmed on the previous QCs that the corresponding PMC microscopist performed smear microscopy within acceptable standard. However it can be operated quarterly or even monthly if PMC microscopist has been newly recruited or showed unacceptable proficiency on the previous QC. The frequency of QC and whether the slides will be selected from the slide boxes, PMC sent, of on the spot during supervisory visit should be determined according to manpower and financial situation.
