Thrombophilic tests

Pre-analysis
- patients should fullfilled screening criteria
- the tests should be performed before patients receive anticoagulant

Antithrombin deficiency
- blocks factor Xa and factor IIa (also factor IXa)
- the tests are made separately for factor Xa and IIa
- antithrombin activity tests:
  - antithrombin in the plasma of the patients binds with heparine in the reagens. Together they bind to FXa. The unbound FXa will be measured (it will bind with the substrates and measured).
 - the results are compared relative to the measurement of pooled plasma from normal patients.
 - in our lab <80% is considered as deficient.
 - remember that heparine cofactor can also bind to FIIa (not to FXa) and will lead to overesttimation of results.

- other tests are for example rocket immunoelectrophoresis that measure the antigen itself.

Protein C deficiency
- type I (low quantity), type 2 (low functionality)
- immunogenic, chromogenic techniques, and chromogenic with APTT

Protein S deficiency
- blocks factor VIIIa and Va
- assay is performed by measuring the activated protein C (the product), the activation is by the snake venom.

APC resisistency
- to measure factor V Leiden (the most common cause of non-challenged venous thrombosis)
- assay is by adding patient plasma with factor V deficient plasma. This mix is added with APTT reagens. The latter mix is added with APC and the other without APC. The ratio of the two is measured.