Thrombin Time Test
Thrombin Time (TT)
Key Points
- Measures the time taken for plasma to clot after adding thrombin
- Specifically evaluates the final step of the coagulation cascade
- Sensitive indicator of fibrinogen disorders and presence of heparin
- Normal range: typically 14-21 seconds (varies by laboratory)
Overview
Thrombin Time (TT) is a specialized coagulation test that measures the conversion of fibrinogen to fibrin in citrated plasma. It bypasses the intrinsic and extrinsic pathways, directly assessing the final common pathway of the coagulation cascade.
Primary Indications
- Evaluation of unexplained bleeding in pediatric patients
- Monitoring of heparin therapy
- Assessment of fibrinogen disorders
- Investigation of dysfibrinogenemia
- Screening for presence of direct thrombin inhibitors
Clinical Scenarios
- Preoperative screening in patients with bleeding history
- Evaluation of neonatal bleeding disorders
- Assessment of fibrinogen function in critically ill children
- Monitoring anticoagulation therapy
Test Procedure
- Collection of citrated plasma sample
- Sample preparation and standardization
- Addition of standardized thrombin reagent
- Measurement of clotting time
Critical Considerations
- Sample must be processed within 4 hours of collection
- Proper sample collection and handling is crucial
- Temperature control during testing is essential
- Reagent standardization affects results
Age-Specific Reference Ranges
- Neonates (0-30 days): 15-23 seconds
- Infants (1-12 months): 14-21 seconds
- Children (1-16 years): 14-21 seconds
Factors Affecting Reference Ranges
- Laboratory methodology
- Reagent concentration
- Patient age
- Pre-analytical variables
Prolonged Thrombin Time
- Hypofibrinogenemia or dysfibrinogenemia
- Presence of heparin or direct thrombin inhibitors
- FDPs or D-dimers interference
- Severe liver disease
Clinical Correlation
- Must be interpreted alongside other coagulation tests
- Consider pre-analytical variables
- Evaluate treatment response
- Monitor disease progression
