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Virological diagnostic services - centralised or local?


A lot of resources are needed to set up a diagnostic virology service in comparison to most other branches of pathology. The actual demand for virological testing is not as great as other branches of pathology, such as haematology, biochemistry, or bacteriology. Therefore, it is probably not justified to set up a diagnostic virology service in every district hospital. However, both central and local virological diagnostic services have their own advantages and disadvantages. The following are points that should be considered.

Range of services - without doubt, a central laboratory can provide a larger range of diagnostic services than a local laboratory because a central laboratory would have greater resources available. For example, it may only be practical for a local laboratory to carry out HBsAG testing whereas a central laboratory would be able to offer test for the full range of hepatitis B markers. Costwise, it may not be practical for a local laboratory to have facilities for electron microscopy whereas it would be justified in the case of a central laboratory. A central laboratory may also be able to offer in house tests for which there are yet to be any commercial tests available or those which are available commercially are of a lower standard. eg. parvovirus serology. Molecular biology techniques such as blotting and polymerase chain reaction would be more appropriate to a central laboratory than a local laboratory.

Reliability of results - in theory at least, the results generated by a central laboratory would be more reliable than that of a local laboratory. A central laboratory would have greater access to confirmatory tests. In addition, because of the increased resources available, it might be able to purchase more expensive equipment for better assays. Because of the greater purchasing power, assay kit and equipment manufacturers would be keener to let a central laboratory to try out new products than local laboratories. As a result, a central laboratory is likely to have access to more up to date tests and equipment. It would also be easier for staff to be trained at a larger central laboratory than a smaller local laboratory.

Cost - because of economies of scale, it should cost less for a central laboratory to process an individual specimen than a local laboratory. A greater number of specimens can be tested each time, resulting in savings of reagent cost and laboratory technician time. Because of the greater purchasing power available, a central laboratory may be able to obtain a cheaper price from assay kit manufacturers than a local laboratory. A central laboratory may also use cheaper in house tests. However, any savings in cost per specimen must be balanced against transport costs involved in sending specimens form a local laboratory to a central laboratory. It is also advisable to put expensive but not routinely used equipment in a central laboratory, such as DNA sequencers and automated nucleic acid extraction machines.

Research - a central laboratory would be in a much better to carry out research than a local laboratory. It would be able to see epidemiological trends much more clearly because of the greater number of specimens which are tested. It would also be in a better position to carry out non-epidemiological research, such as to monitor the response of hepatitis B carriers to interferon therapy by measuring the HBV DNA levels.

Turnover_time - a local laboratory would have a faster turnover time for each request for investigation than a central laboratory. This is because the time needed for transportation from a local laboratory to a central laboratory would be eliminated. There would also be less bureaucracy involved in the processing of specimens. This is a particularly important consideration for diseases for which rapid viral diagnosis is possible and desirable, such as immunofluorescence of nasopharyngeal aspirates for RSV, or the DEAFF test for CMV in immunocompromised patients. However, it is not always necessarily true that a local laboratory would have a faster turnover time since because smaller numbers of specimens are involved, the local laboratory may wait until a certain number of specimens are received before carrying out a specific assay.

Error - the extra step involved in sending the specimens from a local laboratory to a central laboratory makes the possibility of error more likely. A mix-up of specimens may occur during any stage of the process eg. at the splitting stage, or the transcription of results.

Liaison_with_clinicians - a medical microbiologist or a virologist based in a local laboratory would be better placed to liaise with local clinicians about odd clinical problems than those which are based in a central laboratory.

Therefore, both central and local virological diagnostic services have strong and weak points in their favour. The balance though, is in the favour of a centralised service. It may be able to offer the best of both worlds though, by providing some simple and rapid services at the local level and leaving the more complex and less urgently required tests to the central laboratory.

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