Hemolysis has been cited as the most common cause of preanalytical error. How can sample hemolysis be avoided?
A: Many variables contribute to the ability to obtain a high quality, non-hemolyzed blood sample. Controlling the flow of blood between the vein and the tube is really the basis of a good sample collection. Factors that influence the flow of blood include needle gauge, force of suction, size and quality of the vein, and the device used for collection. Direct transfer into vacutainer tubes will control the flow from the needle into the tube, minimizing hemolysis during transfer. When drawing blood into a syringe, the force of suction should be minimal. A good tip is to pull the syringe back and fill it a bit at a time to control the flow. The same goes for transferring from syringes into collection tubes. Allowing the vacutainer to pull the blood into the tube—rather than pushing—maintains appropriate pressure.
How should laboratories examine samples to identify hemolysis?
Automated hemolysis index measurements on chemistry analyzers are fast and very reliable at detecting the presence—and relative quantification—of hemoglobin in a sample. Compared to visual examination, automation is more sensitive and reproducible in detecting the presence of hemoglobin and distinguishing it from similar colored interferents, such as bilirubin. Significantly, automation also allows direct electronic communication to the laboratory information system.
How hemolyzed is too hemolyzed?
The answer will differ for each analyte. Chemistry analyzer manufacturers often provide guidelines for the level of hemolysis that could cause a clinically significant change in results for individual analytes. But there are no standard guidelines to link the amount of hemoglobin spillage to changes in laboratory results. Correction factors associating free hemoglobin concentration with change in potassium results have been published, but are not recommended because the relationship likely differs between individuals.
In our lab, we took a different approach to answering this question. When we were implementing a new chemistry analyzer, we used our laboratory data to identify the point at which hemolysis caused clinically significant changes in certain analytes with high intracellular concentration. This approach allowed us to optimize the flags in the electronic medical record (EMR). Now we alert clinicians only when there is a high likelihood of a clinically significant change in result. In this era of abundant electronic information, alert fatigue is a reality. Labs need to be savvy about providing clinicians with appropriate and actionable alerts.
How should we report hemolyzed results to physicians?
Deciding whether to report or cancel results depends on the analyte and the degree of hemolysis. One must be cautious in cancelling hemolyzed samples outright, as the patient could be experiencing in vivo hemolysis, in which case the results would be
physiologic and delaying reporting could lead to clinician frustration and a potential negative impact on care.
Many labs, including ours, choose to report all but the most severely hemolyzed samples with a comment stating that the sample is hemolyzed and may alter the laboratory result. Adding qualifiers to comments about the degree of hemolysis can aid physicians in judging how affected the result may be. However, as with any comment, it is important to be aware of how your EMR displays laboratory results. Are the comments or flags easily visible to clinicians in all areas where results appear? Even the most informative comment is meaningless if no one reads it.
Can the laboratory be effective in improving hemolysis rates?
Absolutely! In our hospital, the combined efforts of requiring education on blood collection for nurses and house staff, standardizing draw practices and equipment, aligning flags with clinical significance, and offering unit-specific feedback decreased our hospital-wide hemolysis rate by nearly 50% for all inpatients. We continue to promote the mentality that quality samples lead to quality results.
Christine Schmotzer, MD, is director of clinical chemistry at University Hospitals Case Medical Center. She also serves as medical director of the University
Hospitals Translational Laboratory and is an assistant professor of pathology at Case Western Reserve University.