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Laboratory evaluation

The prevalence of unrecognized disease that impacts upon surgical risk is very low in healthy individuals. Nevertheless, many laboratory tests have been performed in this group of patients out of habit and medicolegal concern, with little benefit and a high incidence of false positive results. In a study of 2000 patients undergoing elective surgery, only 0.22 percent of these revealed abnormalities that might influence perioperative management. The selective use of laboratory tests in healthy patients can actually reduce medicolegal risk. Tests ordered in screening panels are frequently not acted upon prior to surgery, thereby creating an additional medicolegal risk.



Normal test values are usually arbitrarily defined as those occurring within two standard deviations from the mean, thereby insuring that 5 percent of healthy individuals

who have a single screening test will have an abnormal result. As more tests are ordered, the likelihood of a false positive test increases; a screening panel containing 20 independent tests in a patient with no disease will yield at least one abnormal
result 64 percent of the time. Aside from possibly causing patient alarm, the additional testing prompted by false positive screening tests leads to unnecessary costs, risks, and a potential delay of surgery.

A selective approach to screening based upon known or clinically suspected illness has been supported in several studies.

In addition, it is probably safe to use laboratory test results that were performed and were normal within the past four months as preoperative tests unless there has been an interim change in clinical status. Fresh tests when reordered within a short span of time provide little new information.