Synonym: Heparin Neutralized Thrombin Time

SPECIMEN: Blue (citrate) top tube; fill tube; separate plasma and refrigerate if necessary. Determination must be done within 2 hours from the time of collection.

Correction of prolonged thrombin time if due to heparin.

Protamine sulfate is added to test plasma and thrombin time is determined.

This test is ordered to confirm that a prolonged thrombin time is due to the presence of heparin, and not other causes. Protamine sulfate will fully correct a prolonged thrombin time due to heparin up to 2.5 U/mL but will have little or no effect on a prolonged thrombin time due to hypofibrinogenemia or inhibitors of fibrin polymerization such as fibrin split products (FSP), paraproteins or dysfibrinogenemia.

Other approaches are also available to confirm a heparin effect on the thrombin time. Heparinase may be added to enzymatically destroy heparin. Alternatively a reptilase time may be run. In contrast to thrombin, this agent is not inhibited by heparin.