Hemolysis refers to the release of hemoglobin and other intracellular components of erythrocytes into the extracellular space of blood. It can occur both in vivo and in vitro – in vivo referring to a result of disease or true hemolytic anemia, and in vitro referring to a number of procedures related to specimen handling. In vivo hemolysis has a large differential, but this comprises an estimated 2% of hemolyzed samples. In vitro hemolysis can be related to phlebotomy technique – incorrect needle size, improper tube mixing, incorrect filling of tubes, prolonged tourniquet. It could also be associated with extreme temperatures, delayed processing, and prolonged storage.
Depending on your local lab, they may have various methods of identifying hemolyzed samples. Some rely on visual inspection, which compares a centrifuged sample to a color chart showing corresponding concentrations of free hemoglobin; visual assessment can be highly inaccurate. Many analyzers are now capable of automated assessments using a hemolysis index that has been standardized. When it comes to reporting, some labs choose to simply note that the sample must be rechecked without reporting any values. However, this can lead to delay in diagnosis of true in vivo hemolysis. Many labs opt to report the values but denote that the sample was hemolyzed. So – if you don’t have any concern for true hemolysis, the cause of hemolysis could be anything from the point of puncture all the way to the time of sample processing.
References: Hemolyzed Specimens: Major Challenge for Identifying and Rejecting Specimens in Clinical Laboratories