Which part of thromboelastography (TEG) tells us about platelet function?

Maximum Amplitude (MA) in TEG Reflects Platelet Function

The Maximum Amplitude (MA) parameter in thromboelastography (TEG) primarily reflects platelet function and contribution to clot strength. 1

Understanding TEG Parameters and Platelet Function

• TEG provides a global assessment of hemostasis, with different parameters reflecting specific aspects of coagulation 1
• Maximum Amplitude (MA) represents the maximum strength of the clot and primarily reflects platelet function and fibrinogen contribution 1, 2
• Decreased MA suggests thrombocytopenia or platelet dysfunction 1
• Increased MA indicates hypercoagulability 1

Platelet Contribution to Clot Strength

• Studies have shown that platelets contribute approximately 80-90% to the overall clot strength as measured by MA 3, 4
• In a study using cytochalasin D (an inhibitor of platelet function), MA was dramatically reduced, confirming the critical role of platelets in determining clot strength 4
• When platelet function is inhibited, MA decreases significantly, demonstrating that MA is highly dependent on platelet activity 5

Limitations of TEG in Assessing Platelet Function

• Standard TEG is insensitive to antiplatelet agents and cannot reliably detect platelet dysfunction 2
• TEG cannot assess the contribution of endothelium to coagulation, so it cannot detect von Willebrand disease or other conditions affecting endothelial adherence 2
• For comprehensive platelet function assessment, TEG should be supplemented with other more sensitive platelet function tests 2, 6

Advanced TEG Methods for Platelet Function Assessment

• Modified TEG techniques have been developed to better assess platelet function:
  • TEG Platelet Mapping uses specific platelet agonists to evaluate platelet reactivity 1
  • The contribution of platelets to clot strength can be quantified by comparing standard TEG with modified TEG using platelet inhibitors 2
  • Some studies suggest calculating platelet contribution by subtracting the maximum clot elasticity of FIBTEM from EXTEM in ROTEM systems 2

Clinical Implications

• When interpreting MA values, clinicians should consider that:
  • Low MA values may indicate need for platelet transfusion 2
  • High MA values suggest hypercoagulability and potential thrombotic risk 1
  • MA should be interpreted in clinical context, as pregnancy and other conditions naturally cause increased MA values 1

Common Pitfalls in TEG Interpretation

• Anemia can paradoxically show hypercoagulable TEG results with increased MA due to decreased blood viscosity 1
• TEG shows high coefficients of variance (7.1-39.9%) for parameters, so results should be interpreted with caution 1, 7
• Results vary between devices and are not interchangeable between TEG and ROTEM systems 1
• TEG is performed at 37°C and cannot assess effects of hypothermia on coagulation 2

In summary, while MA is the primary TEG parameter reflecting platelet function and contribution to clot strength, standard TEG has limitations in detecting specific platelet disorders or dysfunction. For comprehensive assessment of platelet function, TEG should be used in conjunction with other more sensitive platelet function tests.