Have you ever undergone the same blood test at two different laboratories and received slightly different results? It can be confusing and sometimes worrying. The immediate thought is often, “Which report is correct?” The answer is that a difference does not necessarily mean that one laboratory is wrong. Laboratory results are measurements, and like all measurements, they have some degree of analytical variation and biological variation . Pre-analytical variation is one of the most important and frequently overlooked causes of variation. The following factors can influence laboratory results: Fasting or non-fasting status Time of sample collection Exercise before collection Posture Stress Dehydration Prolonged tourniquet application Difficulty during blood collection Hemolysis Lipemia Icterus Delay in transportation Improper temperature during transportation Incorrect tube Inadequate mixing Delayed separation of serum/plasma There ca...