Trusting numbers: uncertainty and the pathology laboratory.

Diagnostic laboratories are increasingly seen as no more than "factories" that generate fast, reliable test results. The dangers of complacency about the use of tests are highlighted by recent cases of unnecessary surgery and chemotherapy based solely on false-positive test results. There are many causes of misleading laboratory data that can potentially lead to clinical mismanagement. Re-emphasis of the value of patient-relevant communication between the requesting doctor and the laboratory, and better undergraduate and postgraduate education about the appropriate use of tests, will help reduce the risks of test results leading to harm.