Quality Control in Clinical Virology
Quality Control Slide Set
Quality control in the clinical laboratory consists of a set of procedures designed to help ensure delivery to the medical staff of laboratory results that are consistent and accurate. These results must be supplied in a timely fashion while the data is still clinically relevant. A clinical virology laboratory should be designed in a manner so that biohazard risks to the laboratory personnel and the general public is minimized and that cultures are protected from environmental contamination. A facility designed specifically for clinical virology should;-
Two sets of written procedures are important. One is for use by medical staff and the other for laboratory use as procedure manuals. The procedures for medical staff should include;-
The procedure manual used in the laboratory should be complete enough in detail so that an inexperienced technologist can perform the procedure without additional information. One copy of the manual should be readily available to bench personnel, another copy should be stored separately in case of accidents.
Specimens for viral isolation are often held for long periods of time before it reaches the laboratory. Enveloped viruses such as RSV and CMV are extremely liable to room temperature and freeze-thaw cycles whereas non-enveloped viruses such as enteroviruses tolerate these conditions well. As a general rule, viral specimens held for short periods should be refrigerated, while those for longer periods may be frozen at -20 or -70oC.
Transport Media - the composition and type of viral transport media can affect viral isolation rates. In general, the media should be a balanced isotonic solution at physiological pH. It should contain a substance that will stabilize the virus such as gelatin, fetal calf serum or bovine serum albumin, and antibiotics against bacteria and fungi. The swab should be made of a material that is non-toxic to viruses, such as dacron or rayon.
Smears - smears are becoming increasingly popular because of the rapidity of staining techniques. The smear should contain a reasonable number of cells, be of a reasonable size and not over-contaminated by blood or pus, as the latter may lead to nonspecific staining.
Specimens for Serology - Excessively haemolysed, lipaemic, bacterially contaminated, or leaking specimens should be rejected. Sera should be heat-inactivated depending on the tests to be performed. In the event of a specimen being rejected, the ward must be informed, preferably by an oral report followed by a written one. Extenuating circumstances may warrant the acceptance of a substandard specimen.
Tissue Culture and Media
Tissue culture remain the mainstay of non-serologically viral diagnosis. Therefore, adequate quality control for commercially purchased or for in-house preparation of tissue culture cells is of great importance. Within a given cell line, there may be significant variations in sensitivity to virus isolation which may depend on the particular cell subline or clone and the passage number. Information on a particular cell line should be recorded pertinently including the source, type, passage number, confluency and cell condition. The loss of a cell line routinely passaged for use can lead to a severe disruption of workflow and therefore, provisions must be made for back-up cells in the event of contamination or laboratory accident. These back-up systems include;
Cells purchased from a commercial company should be certified to be free from mycoplasma, fungal, and bacterial contamination and examined for contamination on receipt. Tissue culture lines carried in-house should be subjected to;
Other quality control procedures that may aid in minimizing the risk of contamination include the exclusion of laboratory with infectious diseases from handling tissue culture, separate laboratory apparel, reagents and glassware for tissue culture. Cell lines should be handled separately and the cabinet be decontaminated in between.
Media - following filter sterilization, aliquots of the media should be taken and checked for bacteriological or fungal investigation. These samples should be examined daily for 5 days and should be free from contamination before that lot of medium is released for use. Aliquots of all other medium components such as fetal calf serum and L-glutamine should also be checked. New lots of medium and fetal calf serum that have passed the sterility check should be monitored for their ability to support cell growth.
Reagents and Kits
Reagents and kits should be ordered from reputable manufacturers or dealers with reliable transportation systems. Upon receipt, the reagents should be checked for obvious breakage or contamination. The quantity, source, lot number and date of receipt should be entered in a logbook and the reagents stored according to the manufacturers storage specifications. When new lots of any reagent are opened, the date should be noted on the container. Caution must be exercised in the case of kits as different components of a kit may have different storage conditions and expiration dates.
Laboratory instruments should be subjected to routine preventive maintenance and checked and calibrated on a regular basis. Some of these checks can be performed by laboratory staff and entered into a logbook. The following are some recommendations for routine laboratory maintenance and performance checks on instruments.