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
