Preanalytical and analytical factors affecting laboratory results.

The results of laboratory tests have a substantial role in the diagnostics of diseases. However, laboratory results do not always correspond with the patient's clinical status. They may be unexpected and surprising. On the other hand, an abnormal laboratory result may be accepted as such and interpreted as a sign of a disease. However, an abnormal result may result from several factors other than disease. Conventionally, these interfering factors have been divided into preanalytical and analytical factors and furthermore into factors acting in vivo and in vitro. The list of these factors is long and laborious to bear in mind. In this review we focus on the factors which, in practice, most often affect laboratory results in healthy individuals and which explain an unexpected result.