Quality assurance programmes are an efficient way of maintaining the standards of performance of diagnostic laboratories, and of upgrading those standards where necessary. In microbiology, quality goes beyond technical perfection to take into account the speed, cost, and usefulness or clinical relevance of the test. Laboratory tests in general are expensive and, with progress in medicine, they tend to use up an increasing proportion of the health budget.
To be of good quality, a diagnostic test must be clinically relevant, i.e. it must help in the prevention or treatment of disease. Other measures of quality in a diagnostic test are:
• Reliability: Is the result correct?
• Reproducibility: Is the same result obtained when the test is repeated?
• Speed: Is the test rapid enough to be of use to the doctor in prescribing treatment?
• Cost–benefit ratio: Is the cost of the test reasonable in relation to the benefit to the patient and the community?
Sources of error may include the following:
• Personnel. The performance of the laboratory worker or technician is directly related to the quality of education and training received, the person’s experience, and the conditions of employment.
• Environmental factors. Inadequate working space, lighting, or ventilation, extreme temperatures, excessive noise levels, or unsafe working conditions may affect results.
• Specimens. The method and time of sampling and the source of the specimen are often outside the direct control of the laboratory, but have a direct bearing on the ability of the laboratory to achieve reliable results.
Other factors that the laboratory can control and that affect quality are the transport, identification, storage, and preparation (processing) of specimens.
The laboratory therefore has a role in educating those taking and transporting specimens. Written instructions should be made available and regularly reviewed with the clinical and nursing staff.
• Laboratory materials. The quality of reagents, chemicals, glassware, stains, culture media, and laboratory animals all influence the reliability of test results.
• Test method. Some methods are more reliable than others.
• Equipment. Lack of equipment or the use of substandard or poorly maintained instruments will give unreliable results.
• Examination and reading. Hurried reading of results, or failure to examine a sufficient number of microscope fields, can cause errors.
• Reporting. Transcription errors, or incomplete reports, cause problems.
Quality assurance in the microbiology laboratory
Quality assurance is the sum of all those activities in which the laboratory is engaged to ensure that test results are of good quality. It must be:
Comprehensive: to cover every step in the cycle from collecting the specimen to sending the final report to the doctor
Rational: to concentrate on the most critical steps in the cycle;
Regular: to provide continuous monitoring of test procedures;
Frequent: to detect and correct errors as they occur.
Quality assurance helps to ensure that expensive tests are used as economically as possible; it also determines whether new tests are valid or worthless, improves the performance of clinical and public health laboratories, and may help to make the results obtained in different laboratories comparable.
Types of quality assurance
There are two types of quality assurance: internal and external.
• Internal. This is called QUALITY CONTROL. Each laboratory has a programme to check the quality of its own tests. Internal quality control involves, ideally: Continuous monitoring of test quality; Comprehensive checking of all steps, from collecting the specimen (whenever possible) to sending the final report.
• External. This is called QUALITY ASSESSMENT. Laboratory performance is controlled by an external agency. In some countries, participation is mandatory (regulated by the government) and required for licensure. External quality assessment involves: Periodic monitoring of test quality; Spot checking of identification tests, and sometimes of isolation techniques.