Tuberculosis Laboratory: Quality Assurance
S. J. Kim, Korean Institute of Tuberculosis, Korean National TB Association
I. Introduction
The laboratory plays a key role in the diagnosis of tuberculosis (TB) patients and in monitoring their response to chemotherapy. In addition the important epidemiological figures such as incidence and prevalence of TB are derived from the laboratory results. Hence the reliable laboratory results are prerequisite for an efficient implementation of TB control programme and can be maintained only by permanent set up of efficient quality assurance (QA) system. Quality assurance is a system for continuously improving reliability, efficiency, and utilization of laboratory services. The elements of QA are structure, process, and outcome and its performance components are quality control (QC), proficiency testing (PT), and quality improvement (QI). QC is a process of internal monitoring to determine the competence of diagnostic services; PT is designed to evaluate the proficiency of the participating laboratories by comparing their results to those obtained in other laboratories (intermediate and national reference laboratories); QI is a process by which the components of diagnostic services are analyzed with the aim of looking for ways to permanently remove obstacles to success.
There are a variety of laboratory procedures that are in use for the TB control programme and that have different technical complexity and require different technical skills or education of the workers. Therefore it is not easy to set up and implement QA system at maximum efficiency to maintain highest possible accuracy and reproducibility of the laboratory results. A variety of quality assurance system are in operation according to the local situation, however their efficiency is in question mainly due to absence of reasonable norm for development of the standard QA system suitable to the local condition.
II. Quality assurance of smear microscopy
The smear microscopy is an utmost important procedure to be organized in the national TB control programme because it permits to detect most of cases who spread infection in the community and their treatment monitoring. Hence the priority for QA implementation should be rendered to achieve the highest possible level of sensitivity and specificity of smear microscopy. Despite technical simplicity of smear microscopy, person to person variation in the proficiency does occur under any setting and leads to inaccurate results mainly due to a minor technical deviation or error. To provide smear microscopy results with an acceptable accuracy and reproducibility on the constant basis, it is essential to make a regular check of everything used and done in the laboratory and of every result obtained. However it is not easy to set up a comprehensive and feasible QA system for smear microscopy within acceptable efficiency.
1. Organization
In general the quality assurance is implemented by the higher level laboratory. At the early stage of organization of tuberculosis laboratory services the national reference laboratory (NRL) should have a responsibility of QA over the peripheral laboratory (PL) performances. However increasing number of PL makes NRL unable to cover whole country, thus the intermediate laboratories should practice QA of the PL 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 QA of the other laboratories.
In order to maintain technical proficiency, the laboratory needs to examine at least 800 smears per year. The peripheral multipurpose laboratories located in rural area usually examine small number of smears (less than optimum workload) while the laboratories in urban are often overloaded. In the laboratory where less than 10 smears are examined per day on an average there may be no independent worker for TB smear microscopy. However it is desirable to perform by independent worker if more than 10 smears have to be examined a day. And if more than 30 smears have to be examined, use of fluorescence microscopy should be considered because it can increase the capacity by about 5 folds.
2. Quality control
QC covers all measures taken by the laboratories themselves in order to monitor the accuracy and reproducibility of the results they issued. One of the important measures could be check of staining capacity and contamination with environmental acid-fast bacilli of new batch of stains they prepared, purchased or received from the outside.
