What is the normal kaolin‑activated thromboelastography (TEG) R‑time, what causes prolonged or shortened values, and how should they be managed?

Normal Kaolin-Activated TEG R-Time and Clinical Management

Normal Reference Range

The normal kaolin-activated TEG R-time is typically 4-8 minutes, representing the time from test initiation to initial fibrin formation. 1

Causes of Prolonged R-Time

Anticoagulant Effects

• Heparin therapy (unfractionated or low molecular weight) prolongs R-time by inhibiting thrombin generation 2
• Direct oral anticoagulants (dabigatan, factor Xa inhibitors) cause R-time prolongation 1
• Vitamin K antagonists (warfarin) prolong R-time through factor deficiency 1

Coagulation Factor Deficiency

• Dilutional coagulopathy from massive fluid resuscitation or hemorrhage causes prolonged R-time 1
• Liver disease results in decreased synthesis of coagulation factors, prolonging R-time 3
• Congenital factor deficiencies (hemophilia, factor VII deficiency) prolong R-time 1

Causes of Shortened R-Time

Hypercoagulable States

• Pregnancy physiologically shortens R-time due to increased coagulation factors, with progressive decreases correlating with pregnancy advancement 1
• Post-cesarean delivery causes even shorter R-time, peaking at 3 hours postoperatively 1
• Malignancy, inflammatory states, and inherited thrombophilias accelerate clot initiation 1
• Enhanced thrombin generation from any cause results in shortened R-time 1

Management of Prolonged R-Time

Reversal of Anticoagulation

• For warfarin: administer prothrombin complex concentrate (PCC) along with intravenous vitamin K, with dosing guided by INR level 1
• For dabigatran: administer idarucizumab (Praxbind) and monitor reversal effectiveness with TEG 1
• For factor Xa inhibitors: administer andexanet alfa or PCC, monitoring with anti-Xa assays rather than TEG alone 1

Treatment of Coagulopathy

• For dilutional coagulopathy: administer fresh frozen plasma (FFP) 10-15 mL/kg as first-line treatment 1
• Consider fibrinogen concentrate (4g/70kg) if significant hemodilution (>50%) is present 1
• In massive transfusion scenarios, maintain a 1:1:1 ratio of packed RBCs, FFP, and platelets 1
• Repeat TEG 15-30 minutes after intervention to assess response, targeting R-time normalization (typically <8 minutes) 1

Management of Shortened R-Time

Anticoagulation for Hypercoagulability

• For severe hypercoagulability or high thrombotic risk, initiate therapeutic anticoagulation with low molecular weight heparin (LMWH) or unfractionated heparin (UFH) 1
• LMWH is preferred over UFH in pregnant patients due to better safety profile and more predictable anticoagulant effect 1
• The anticoagulant effect on TEG is defined as a difference >25% between plain and heparinase R-time samples 1

Risk Stratification

• Evaluate for underlying hypercoagulable conditions including pregnancy, malignancy, inflammatory states, or inherited thrombophilias 1
• In pregnancy, shortened R-time is physiologic and may not require correction unless extremely elevated with clinical thrombotic risk 1

Important Technical Considerations and Pitfalls

Sample Processing Timing

• Kaolin-activated citrated TEG specimens should be processed within 30 minutes of collection to avoid artifactual hypercoagulability 4
• Processing can begin as early as 15 minutes post-venipuncture, but delaying beyond 30 minutes causes progressive shortening of R-time, falsely suggesting hypercoagulability 4, 5
• Storage of citrated whole blood significantly affects TEG variables in a hypercoagulable direction, with R-time affected by 12% when comparing 0 and 30 minute storage times 5

Correlation with Conventional Tests

• R-time shows weak and inconsistent correlation with INR and aPTT in critically ill patients, particularly those with liver disease 3
• In ECMO patients, moderate correlation exists between INTEM clotting time and standard coagulation tests (R² = 0.34 for aPTT, 0.3 for ACT), but no significant correlation with kaolin R-time 2
• TEG provides complementary but not interchangeable information compared to conventional coagulation tests 2

Device and Methodology Variations

• Results vary between different TEG systems and are not interchangeable between TEG and ROTEM devices 1
• Use device-specific reference ranges, as results vary between different TEG systems 1
• TEG shows high coefficients of variance (7.1-39.9% for TEG parameters), requiring interpretation in clinical context 1

Clinical Context Considerations

• In pregnancy, baseline R-times are typically shortened due to physiologic hypercoagulability; pregnancy-specific reference ranges must be used 1
• 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 effects of hypothermia on coagulation 1
• Anemia can paradoxically show hypercoagulable TEG results due to decreased blood viscosity 1