Evaluating hemostatic risk is critical in both clinical and therapeutic settings, and analytical coagulation assays play a central role in this process. These assays provide functional insights into the balance between procoagulant and anticoagulant forces within the blood. By measuring specific factor activities, global clotting potential, or thrombin generation, these tools help identify bleeding or thrombotic tendencies—supporting diagnosis, risk stratification, and treatment monitoring across a range of coagulation disorders.

Prothrombin Time (PT)

What it measures: The extrinsic pathway of coagulation, primarily Factor VII, and the common pathway (Factors X, V, II, and fibrinogen).

Hemostatic risk relevance: Prolonged PT/INR indicates potential bleeding risk and is commonly used to monitor warfarin therapy or detect liver dysfunction and vitamin K deficiency.

Activated Partial Thromboplastin Time (aPTT)

What it measures: The intrinsic and common coagulation pathways (Factors XII, XI, IX, VIII, X, V, II, and fibrinogen).

Hemostatic risk relevance: Prolongation can signal deficiencies in intrinsic pathway factors (e.g., Hemophilia A or B) or the presence of inhibitors, increasing bleeding risk. Shortened aPTT may suggest hypercoagulability.

Thrombin Generation Assay (TGA)

What it measures: The amount and rate of thrombin formation in plasma over time—offering a global assessment of coagulation potential.

Hemostatic risk relevance: Elevated thrombin generation can indicate thrombotic risk, while decreased generation is associated with bleeding disorders or anticoagulant therapy. TGA is especially useful in assessing mild or complex coagulation disorders, including FXI deficiency.

Thromboelastography (TEG®)

What it measures: The viscoelastic properties of whole blood clot formation over time, including clot initiation, formation, strength, and dissolution. Key parameters include R-time, K-time, alpha angle, maximum amplitude (MA), and lysis at 30 minutes (LY30).

Hemostatic risk relevance: TEG provides a global, real-time assessment of coagulation function, incorporating clotting factors, platelets, fibrinogen, and fibrinolysis. It’s especially valuable in detecting both bleeding risk (e.g., factor deficiency, platelet dysfunction, or hyperfibrinolysis) and hypercoagulability in acute care settings like trauma, surgery, or liver transplantation.

Platelet Aggregation Assays

What they measure: The ability of platelets to clump together in response to specific agonists (e.g., ADP, collagen, arachidonic acid, ristocetin). Performed using light transmission aggregometry (LTA) in platelet-rich plasma or impedance aggregometry in whole blood.

Hemostatic risk relevance: Impaired aggregation indicates platelet function disorders—either inherited (e.g., Glanzmann thrombasthenia) or acquired (e.g., aspirin effect, uremia). These assays help identify bleeding risk when standard coagulation tests are normal and monitor responsiveness to antiplatelet therapy.

Platelet Activation Assays

What they measure: Platelet activation markers on the cell surface (e.g., P-selectin, activated GPIIb/IIIa) or within platelet granules, using flow cytometry, ELISA, or functional assays like serotonin release.

Hemostatic risk relevance: Elevated platelet activation is linked to thrombotic risk in conditions like cardiovascular disease, diabetes, and HIT. These assays also evaluate platelet reactivity in patients on antiplatelet therapy to guide treatment and predict adverse events.

Fibrinogen Assay

What it measures: Functional fibrinogen concentration—the final substrate in the coagulation cascade.

Hemostatic risk relevance: Low fibrinogen levels are associated with bleeding risk (e.g., in DIC or liver disease), while elevated levels can be a marker of thrombotic risk or inflammation.

Anti-Factor Xa Assay

What it measures: Inhibition of Factor Xa activity—used to monitor heparin and low molecular weight heparin therapy.

Hemostatic risk relevance: Ensures therapeutic anticoagulation without tipping into bleeding risk due to overdose.

D-dimer Assay

What it measures: Fibrin degradation products—a marker of active clot breakdown.

Hemostatic risk relevance: Elevated D-dimer suggests recent or ongoing clot formation and lysis, aiding in the diagnosis of venous thromboembolism (VTE) and disseminated intravascular coagulation (DIC).