Thrombin time (TT)

What it measures

Measures how quickly fibrinogen converts to fibrin after thrombin is added. It detects heparin, direct thrombin inhibitors and abnormal or low fibrinogen.

Specimen and preparation

• Specimen: Citrated plasma (3.2% sodium citrate, 9:1)
• Tube: Light_blue top
• Preparation: Avoid heparin contamination from lines.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Heparin contamination or therapy
• Dabigatran or other direct thrombin inhibitors
• Low fibrinogen or dysfibrinogenemia
• High fibrin degradation products (DIC)
• Paraproteins (myeloma)

Method

Clot-based assay with dilute bovine or human thrombin

Good to know

Very sensitive to dabigatran; a normal TT largely excludes significant dabigatran effect. Reptilase time is unaffected by heparin and helps separate causes.

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