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Unnecessary repeat requesting of tests can make up a large proportion of a laboratory's workload. It is often difficult to know whether a repeated request is unnecessary because re-testing may be helpful for many chemistry or haematology tests. This audit set out to establish the size of this problem in an immunology laboratory. This setting is informative because most immunology tests are slow to change and repeat testing within a short time serves no useful clinical purpose. We also tried to identify the circumstances under which these repeat requests were made because this information might suggest what action could be taken to reduce the rate of such requests. We selected three tests commonly requested from the immunology laboratory, the results of which are unlikely to change greatly over short time periods. We analysed the requesting patterns for autoimmune screens (which test for antibodies against nuclei, mitochondria, gastric parietal cells, smooth muscle, and reticulin on a rodent tissue composite block and thyroid antibodies on primate thyroid sections), rheumatoid factor screens, and immunoglobulin values over a 12 month period, identifying tests that were repeated within three months of a previous request. This was achieved by interrogating the CILMS laboratory computer system using a MUMPS enquiry protocol. A total of 25 067 requests were made for these three tests over the year (table 1). Repeat requests within three months of a previous request represented 7.3% of the total workload for these tests. For individual tests the corresponding proportions were: autoimmune screens, 4.5%; rheumatoid factor screens, 4.1%; and immunoglobulin values, 18.7%. The total cost of the tests was estimated at just over £13 000. It is very rare for repeat requests to be indicated for these tests within two to four weeks, so shorter time periods were also analysed. Tests repeated within the two week time period accounted for 2.3% of the total workload for the year. Similarly, repeat autoantibody tests are not indicated within a four week period. Re-requesting of autoimmune screens and rheumatoid factors within a four week period accounted for 2.5% of the total workload for these tests during the year analysed. If this figure is applied across the laboratory's autoantibody repertoire, the cost of such unnecessary tests amounts to nearly £7500. Therefore, it is clear that unnecessary repeat testing is both time consuming and expensive. Possible reasons for repeat testing were sought within the data collected. Tests performed in general practice and then repeated on referral to hospital accounted for only 10.6% of all the tests repeated within three months. Similarly, a change of consultant or location within the hospital only contributed 13%. However, 76.4% of all repeated tests were performed by the same consultant team in the same location. This effect was even greater in the short term, where 82.2% of all tests repeated within a two week period were requested by the same team. Clearly, hospital consultants and their teams should be the target of any intervention to change this requesting behaviour. Feedback of individual test use data to consultants has been shown to reduce overall request frequency for haematology and clinical chemistry tests.1,2 Whether this results in an improvement in clinical care has been contested,3 but with the tests we have analysed there is no doubt that frequent repeats are unnecessary. Test reduplication may also occur simply because the requesting clinician is not aware that the test has already been performed. Where no result is immediately available a new test is ordered rather than checking whether a result is pending. Such behaviour might be modified by an interactive electronic requesting system that gives details of tests already ordered, and may also block the re-requesting of selected tests within a specified time frame. As a result of this audit, this capacity is now a required output specification for our planned new laboratory computer system.