Low R Time on TEG Indicates Hypercoagulability
A low R time on thromboelastography (TEG) indicates a hypercoagulable state, meaning blood is clotting faster than normal, which increases the risk of thrombotic complications. 1, 2
Understanding R Time
- R time (Reaction time) measures the time from test initiation to initial fibrin formation, representing the clotting time or time to clot initiation 1
- Normal R time typically ranges from 5-10 minutes 2
- Values below this range indicate hypercoagulability, reflecting accelerated clot initiation 2
Clinical Significance of Low R Time
Shortened R time reflects increased coagulation activity and has been demonstrated in several clinical scenarios:
- Pregnancy naturally shortens R time due to physiologic hypercoagulability, with progressive decreases correlating with pregnancy advancement 1
- Post-cesarean delivery, R time becomes even shorter (P = .0001), indicating increased hypercoagulability that peaks at 3 hours postoperatively 1
- General anesthesia during cesarean delivery causes significantly decreased R time (P < .01) compared to spinal anesthesia, indicating faster clotting 1
- High and moderate thrombotic risk patients demonstrate shorter pre-operative R times compared to low-risk patients 3
Pathophysiology
Low R time indicates accelerated initiation of the coagulation cascade, which can result from:
- Increased coagulation factor activity 2
- Enhanced thrombin generation 1
- Reduced anticoagulant effect (when anticoagulation is inadequate or absent) 2
Clinical Implications and Management
The primary concern with low R time is increased thrombotic risk, requiring assessment and potential intervention:
- Evaluate for underlying hypercoagulable conditions including pregnancy, malignancy, inflammatory states, or inherited thrombophilias 1
- Consider thromboprophylaxis with low molecular weight heparin (LMWH) or unfractionated heparin (UFH) for severe hypercoagulability or high thrombotic risk 2
- LMWH is preferred over UFH in pregnant patients due to better safety profile and more predictable anticoagulant effect 2
- Monitor for clinical signs of thrombosis including deep venous thrombosis or pulmonary embolism 2
Important Caveats
Context is critical when interpreting low R time:
- In pregnancy, shortened R time is physiologic and may not require intervention unless extremely low or associated with other high-risk features 1, 2
- Pre-operative fluid restriction can artificially lower R time by causing hemoconcentration 3
- Colloid preloading is associated with longer R times compared to crystalloid preloading, so fluid type affects results 1
- TEG is performed at 37°C and cannot assess hypothermia effects on coagulation 2
- Results vary between devices and are not interchangeable between TEG and ROTEM systems 2
Monitoring Response to Intervention
If anticoagulation is initiated for low R time: