Table 6 lists a variety of other essential coagulation assays that may be used to assess a patient. As indicated in Table 7, the test results may be impacted if a patient is treated with a NOAC.
Table 6. Other Coagulation Assays of Importance.| Assay | Description |
| Antithrombin (AT) | AT is the principal physiological inhibitor of thrombin, slowly and irreversibly inhibiting it by forming a stable one-to-one complex. 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. |
| Fibrinogen | When 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 the 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 a poor response to APC. Protein C and cofactor Protein S are responsible for inactivating factors Va and VIIIa, which stops 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 Assay | Expected Impact |
| Antithrombin Activity | Overestimation |
| Activated Protein C resistance (APC ratio) | Overestimation |
| Protein C and Protein S activity | Overestimation |
| Coagulation Factors | Underestimation |
| Factor XIII | Underestimation |
| Fibrinogen | Underestimation |
| Lupus Anticoagulants | Difficult to interpret |
