Impact of NOACs on Other Coagulation Assays

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The page below is a sample from the LabCE course New Oral Anticoagulants. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Impact of NOACs on Other Coagulation Assays

In Table 6, a variety of other coagulation assays of importance may be used to assess a patient. The test results may be impacted if a patient is being treated with a NOAC, as indicated in Table 7.
Table 6. Other Coagulation Assays of Importance.
Antithrombin (AT)AT is the principal physiological inhibitor of thrombin that slowly and irreversibly inhibits thrombin by forming a stable one-to-one complex with thrombin. AT is also the principal physiological inhibitor factor of factor Xa. Normally, AT accounts for the majority of the thrombin inhibitory activity in plasma. Plasma antithrombin inhibitory activity is measured using thrombin or factor Xa as target enzymes.
FibrinogenWhen plasma is diluted and clotted with excess thrombin, the fibrinogen concentration is inversely proportional to the clotting time. Fibrinogen assays are useful in detecting deficiencies of fibrinogen and in detecting an alteration in the conversion of fibrinogen to fibrin.
Protein C and Protein S activity Protein C and Protein S are one of two major inhibitor systems. Methods for the determination of Protein C in plasma can be 1. Antigenic-measures the amount of material present, does not measure function, 2. Chromogenic-measures some but not all functions, 3. Clotting-measures all functions of protein C molecule.
Protein S functional assay is based on cofactor activity with protein C, which enhances the anticoagulation action of APC and is reflected by the prolongation of the clotting time.
Activated Protein C Resistance Activated protein C (APC) resistance is a disorder characterized by poor response to APC. Protein C, along with cofactor Protein S, is responsible for inactivating factors Va and VIIIa which puts a stop to the clotting pathway. With APC resistance, this process ceases to occur and the clotting pathway continues, placing the patient at an increased risk of thrombosis.
when measured with the APTT-based methods.
Lupus anticoagulant (LA) detection LA is an IgM, IgG, or IgA immunoglobulin that does not inhibit the activity of any specific coagulation factor.
LA detection is searched for by means of phospholipid-dependent tests such as the APTT or the dilute Russell viper venom test. LA is the most common cause of a prolonged APTT. LA is a risk factor for thrombosis.
Table 7. Impact of New Oral Anticoagulants on Coagulation Assays.
Coagulation AssayExpected Impact
Antithrombin ActivityOverestimation
Activated Protein C resistance (APC ratio)Overestimation
Protein C and Protein S activityOverestimation
Coagulation FactorsUnderestimation
Factor XIIIUnderestimation
Lupus AnticoagulantsDifficult to interpret