During a normal working day it sometimes happens that results of requested tests point the way to the requirement for other tests to be done. For example a raised total cholesterol result indicates that HDL-cholesterol and LDL-cholesterol would also be helpful to the requester; a raised globulin level could indicate that serum protein electrophoresis might also be done; a raised TSH could suggest that free-thyroxine and free-triiodothyronine might be carried out.
This is helpful to the patient because it means that a second blood collection is not needed and the results will help the requester make a better diagnosis of what is wrong with the patient. At my laboratory, some years ago, we saw that the globulin level was significantly raised in a sample for which tests had been requested by a haematologist. It was the policy of the laboratory at that time to carry out serum protein electrophoresis in such circumstamces. On carrying out electrophoresis it was quite clear that the patient was suffering from paraproteinaemia. We reported the result to the haematologist, but both I and the department were heavily criticised by the haematologist for doing so. We were taken aback by this criticism as we did not believe that the paraproteinaemia would have been diagnosed if we had not done the second-phase of tests.
Some laboratories do not have such policies, probably because their workload is so high that they do not have time to carry out such add-on tests. Others suggest that when a sample has been moved around the laboratory to complete all the requested tests it is not possible to track it down to pursue other "add-on" tests. However those who make this statement also say that it is less work to do this than to deal with a second sample received from the same patient, and say that they think we have to learn to live with this and devise systems, which enable relatively painless addition without too much disruption to subsequent workflow.
Others suggest that there might be an ethical issue involved in doing tests that were not originally requested. But some senior laboratory workers believe that a laboratory request is a referral of the patient's sample and that the laboratory is thus entitled to do all that is necessary on that sample to make the definitive diagnosis.
Sometimes add-on tests are requested by post or by telephone by the requester, who has just received the results of the initial investigations. Often the time-delay in doing this means that the sample has been discarded by the time that the request for add-on tests is received. Clearly this means that the patient must be bled again.
In summary, it is my view that a policy of carrying out "add-on" tests is helpful to the patient because it means that a second blood collection will not be required and that the definitive diagnosis will be available to the requester at an earlier date.
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