Debbie Moffitt from Honolulu posted a question on Pat LeTendre’s Medlab_L earlier this month:
A hematologist is asking for the reptilase time test to distinguish when prolonged partial thromboplastin time (PTT) and thrombin time (TT) results are due to heparin. When heparin is suspected, we use Hepzyme to try to correct the TT or PTT . We also review the patient’s clinical condition, medications, and if the specimen was drawn through a heparin line. We have never had a request for this test before.
My question is, does anyone have experience with reptilase, and what vendors do you use? Chances are we are not going to bring in this test, but I want to know if it is in wide use or not.
George responded: Stago offers a reptilase kit, and it is easy to perform, as the steps are identical to the thrombin time. The reptilase enzyme, a snake venom, is simply substituted for the thrombin. Because reptilase cleaves only fibrinopeptide A from fibrinogen, as opposed to thrombin, which cleaves fibrinopeptides A and B, it is not prolonged by heparin, so when the thrombin time is prolonged and the reptilase time is normal, you’ve confirmed heparin. The trouble is, there is no other current use for the reptilase time and thus no reason to expend the resources to set up the assay. Your approach, neutralizing with Hepzyme plus checking the chart, is the way most of us do it, and if that doesn’t offer enough proof, you can offer the chromogenic anti-Xa heparin assay, which is definitive.
Debbie received several similar responses. Here is her follow-up conclusion: We have used Hepzyme for years. We always keep it on hand although we don’t have to use it often. It has been useful when there is a
question of whether a sample contains heparin in cases of disputed contamination. Simply reconstitute with 1 mL of patient plasma, then re-test the plasma. It neutralizes up to 2 units of heparin per vial. We use commercial heparin controls and test PTT pre and post neutralization.
Deborah Moffitt MT (ASCP)
Diagnostic Laboratory Services
Queens Medical Center