Members of Pat Letender’s Medlab-L have been discussing the effect of hemolysis on coagulation testing. This statement appears in CLSI standard H21-A4:
Samples that have visible hemolysis should not be used because of possible clotting factor activation and end point measurement interference. Some current instruments using an optical detector may have problems with end point determinations on samples that are icteric, lipemic, or contain substances that interfere with light transmission. Alternative methods (e.g., mechanical/electromechanical) should be considered.
There is no reference associated with this speculative statement, so just for fun, I’d like to throw a little heat into the discussion by asking if there is any authoritative evidence for rejecting hemolyzed specimens.
The only publication I’ve been able to find is summarized here:
Laga AC, Cheves TA, Sweeney JD. The effect of specimen hemolysis on coagulation test results. Am J Clin Pathol 2006;126:748-55.
Hemolyzed specimens are rejected for coagulation testing based on concerns of artifactual interference. Prothrombin time (PT), activated partial thromboplastin time (PTT), and selected factor assay test results for consecutive pairs of hemolyzed and subsequently recollected (mean, 72 minutes later) nonhemolyzed patient specimens were compared. Specimens from healthy human subjects were subjected to mechanically induced hemolysis, and PT and PTT results compared with concurrently drawn nonhemolyzed control samples. In 50 paired patient specimens, there were statistically significant differences in PT (15.8 +/- 8.4 vs 16.3 +/- 8.7 seconds, P < .01) and PTT (31.6 +/- 18 vs 32.5 +/- 19 seconds, P < .01) between hemolyzed and nonhemolyzed specimens, respectively. Specimens from healthy subjects showed no difference in PT and a minor difference in PTT. A policy of rejecting hemolyzed specimens for coagulation tests should be revisited because the observed difference, when present, is unlikely to be considered clinically meaningful.
Is the concern for hemolysis real, or is this another “expert opinion” we’ve all bought into without examination? More to the point, do you know of any additional studies that compare paired hemolyzed and non-hemolyzed specimens for activity? If you do, please e-mail them to me and I will post. Geo