Causes, consequences and management of sample hemolysis in the clinical laboratory

Preanalytical hemolysis of blood samples is a common problem in medical practice, especially in emergency departments. Several potential influences on sample hemolysis have been investigated, including sampling techniques, centrifugation and sample transport. In particular, the use of intravenous catheters and the vacuum sampling technique have often been demonstrated to provoke hemolysis. Other factors playing a role include the use of inappropriate puncture sites, complicated blood sampling, prolonged tourniquet application, underfilling of tubes and excessive shaking of specimens. Training of phlebotomists can play a pivotal role in overcoming these issues. A sample may also undergo hemolysis at the point of centrifugation, more specifically when centrifugation lasts too long or is done repeatedly. Pneumatic tube system (PTS)-transported samples tend to be more strongly affected by hemolysis compared to hand-carried ones, though whether this difference is clinically relevant remains questionable. The velocity at which the sample moves, the distance it covers and the shock forces it sustains all determine to what extent hemolysis occurs during PTS transport. The use of cushion inserts in the carrier to stabilize the samples and the presence of a gel separator in the transported serum tubes may prevent PTS-induced hemolysis. Finally, there is considerable variation between patients in the extent to which samples are prone to hemolysis. Sample hemolysis leads to unreliable laboratory results, delayed diagnosis and patients suffering avoidable discomfort. Specifically, hemolysis may interfere with laboratory results due to release of intracellular components, dilution effects, proteolysis and interference with analytical techniques. There is ongoing debate about how laboratories should deal with results altered by hemolysis. Laboratory specialists should clearly communicate with the ordering clinicians in order to make an informed decision about how to interpret hemolysis-affected analytical results. This review looks into current evidence concerning the causes and consequences of in vitro hemolysis, and aims to explain how to deal with it.