TEG Platelet Mapping Analysis
TEG Platelet Mapping (TEG-PM) is a specialized thromboelastography assay designed to assess platelet function by measuring platelet inhibition in response to antiplatelet medications (aspirin and clopidogrel), but current guidelines do not recommend it as a standalone test for platelet function due to significant limitations and lack of validation. 1
What TEG Platelet Mapping Measures
TEG-PM evaluates platelet contribution to clot strength through specific pathways:
- MA(AA): Maximum amplitude after arachidonic acid stimulation (assesses aspirin effect on thromboxane A2 pathway)
- MA(ADP): Maximum amplitude after adenosine diphosphate stimulation (assesses clopidogrel effect on ADP receptor pathway)
- MA(Fibrin): Fibrin contribution to clot strength (measured in heparinized blood)
- MA(Thrombin): Total platelet contribution after thrombin activation
- Percent inhibition: Calculated for both AA and ADP pathways to quantify antiplatelet drug effect
The assay calculates platelet inhibition by comparing clot strength with and without specific platelet agonists 2.
Interpretation Parameters
Normal Values in Healthy Donors
- Thromboxane A2 receptor inhibition: ~1.2% (range 0-10%)
- ADP receptor inhibition: ~18.6% (range 0-58%) - note the high variability 2
- Analytical variation: ~5% for most parameters 2
Clinical Thresholds
- ≥60% inhibition (AA or ADP): Considered significant platelet inhibition 3
- High platelet reactivity: Associated with increased thrombotic risk 4, 5
- Gender differences exist: females show higher MA(Thrombin) than males (62.8 vs 58.4 mm) 2
Critical Limitations You Must Know
Major Technical Issues
The assay has fundamental flaws that compromise reliability:
Heparinized samples cause artifactual platelet activation - In 28% of samples, MA(Fibrin) shows unstable increasing patterns due to unanticipated platelet activation/aggregation in heparinized blood, falsely elevating percent inhibition (ADP inhibition from 19% to 38%, AA inhibition from 29% to 58%) 6
Poor sensitivity to platelet dysfunction - Standard TEG bypasses primary hemostasis and cannot detect platelet disorders, unlike PFA-100 1
High inter-individual variability - ADP receptor inhibition shows CVg of 26.2%, making interpretation challenging 2
Significant overlap between groups - Substantial overlap in platelet receptor inhibition between patients on antiplatelet therapy and controls limits clinical usefulness 7
What TEG-PM Cannot Detect
- Von Willebrand disease
- Endothelial dysfunction
- Platelet adhesion defects
- Reliable platelet function in obstetric patients 1
Clinical Applications (With Caution)
Monitoring Antiplatelet Therapy
TEG-PM can identify statistical differences in platelet inhibition between patients on aspirin/clopidogrel versus controls 7, but:
- Results must be supplemented with other platelet function tests 1
- Clinical outcomes correlation remains poorly validated 8
Thrombotic Risk Assessment
Recent studies suggest potential utility:
- Diabetes and obesity: Associated with increased platelet aggregation and clot strength despite anticoagulation 4
- Post-revascularization: Lower ADP inhibition correlates with major adverse limb events 9
- Trauma patients: Specific abnormalities (elevated R time, increased LY30) associate with mortality 5
Time Course After Drug Withdrawal
In clopidogrel-treated patients awaiting surgery:
- Day 3: 67.1% ADP inhibition
- Day 5: 48.8% ADP inhibition
- Day 7: 36.1% ADP inhibition 7
Practical Recommendations
If you use TEG-PM, follow this approach:
Never rely on TEG-PM alone - Always supplement with conventional platelet function tests (platelet count, PFA-100, or aggregometry) 1
Recognize false results - If MA(Fibrin) shows unstable rising pattern, suspect platelet activation artifact 6
Account for metabolic factors - Diabetes and obesity increase baseline platelet reactivity independent of medication 4
Avoid in obstetrics - Do not use TEG-PM to guide neuraxial anesthesia decisions based on platelet count alone 1
Consider hematocrit effects - Anemia paradoxically creates hypercoagulable TEG appearance despite clinical bleeding tendency 1
Key Pitfall to Avoid
The most dangerous error is assuming normal TEG-PM excludes platelet dysfunction. The assay's design bypasses primary hemostasis, making it insensitive to clinically significant platelet disorders. Previous studies suggesting safety of neuraxial anesthesia with platelet counts as low as 56,000/mm³ based on normal TEG must be interpreted with extreme caution 1.