Thrombophilia

Synonyms: Hypercoagulability, coagulability, hypercoagulable state

Overview
Thrombophilia is the propensity to develop thrombosis (blood clots) due to an abnormality in the system of coagulation.

Indications
Searching for a coagulation abnormality is not normally undertaken in patients in whom thrombosis has an obvious other cause. For example, if the thrombosis is due to immobilisation after recent orthopedic surgery, it is unlikely that an underlying cause is found.

Conversely, although thrombosis itself may occur in any person, repeated (two or more) unprovoked episodes of thrombosis and unusual sites and types of thrombosis (e.g. Budd-Chiari syndrome) may point towards a coagulation disorder.

Increasingly, recurrent miscarriage is seen as an indication for thrombophilia screening.

Classification
Thrombophilia can be classified in various forms.
 * The most common classification is by the nature of the thrombosis: arterial, venous or combined.
 * Crowther & Kelton (2003) propose to classify the abnormality by the molecular deficiency, type I being the (severe) deficiencies of inhibitors, and type II being the less severe elevation of coagulation factors.
 * Acquired vs. congenital

Types
Common types:
 * Factor V, Leiden type (5% of the population are heterozygous for FVL).
 * Prothrombin mutation (G20210A, 5'UTR).
 * High homocysteine levels due to MTHFR mutation or vitamin deficiency (vitamins B6, B12 and folic acid).
 * Antiphospholipid antibodies
 * anti-cardiolipin antibodies and/or
 * lupus anticoagulants
 * Renal disease (renal loss of antithrombin)

Rare forms:
 * Plasminogen and fibrinolysis disorders.
 * Paroxysmal nocturnal hemoglobinuria
 * Protein C deficiency.
 * Protein S deficiency.
 * Antithrombin III deficiency.

Testing
Tests for thrombophilia include prothrombin time and INR, partial thromboplastin time, thrombin time, fibrinogen levels, antiphospholipid antibody levels (IgG- and IgM-anticardiolipin, dilute Russell viper venom time and lupus anticoagulant), protein C, protein S and antithrombin (both levels and activity), activated protein C resistance (APC resistance), factor V Leiden and prothrombin mutation. Many laboratories add on various other tests, depending on local policy and guidelines.