Thrombotic Diorders - All You Need to Know

Introduction

Thrombosis in common parlance is obstructive clot formation within a vessel. Thrombophilia or hypercoagulable state is a tendency to develop venous and (less frequently) arterial thrombosis. The three major pathogenic causes of thrombosis have been identified as changes in the vessel wall, in the blood flow and in the blood composition. Thrombosis is a common pathology underlying ischemic heart disease, ischemic stroke, and venous thromboembolism (VTE) (1). Hypercoagulability plays a major role in the pathogenesis of venous thromboembolism (VTE). As per the survey conducted by WHO in 2016, the top ten global causes of death are led by ischemic heart disease and stroke.

There are two types of thrombophilia; hereditary thrombophilia and acquired thrombophilia. Hereditary thrombophilia is a genetically determined increased risk of thrombosis; acquired or secondary thrombophilia is a physiologic or pathologic condition that predisposes affected persons to thromboembolic diseases (2).

The initial thrombophilia testing should start with a complete personal and family medical history and physical examination. Although a family history of thrombosis is an important selection factor for testing, a negative family history of VTE does not exclude hereditary thrombophilia in a patient provided for testing due to low penetrance of thrombophilic defects and new mutations that may occur. The initial laboratory investigation should begin with Prothrombin Time (PT), Activated Partial Thromboplastin Time (APTT), Thrombin Time (TT) and fibrinogen, in order to exclude anticoagulant therapy that affects the results of many phenotypic assays and also to rule out other clinical conditions associated with acquired coagulation disorders.

(ECL Note: ECL series has primary test menu which starts with Erba PT LS (EHL00023) (For PT assay) and Erba Actime (EHL00003) (For PTT assay))

Laboratory investigation of thrombophilia is aimed at detecting the well-established hereditary and acquired causes of venous thromboembolism, including activated protein C resistance/factor V Leiden mutation, Prothrombin G20210A mutation, deficiencies of the physiological anticoagulants anti-thrombin, protein C and protein S, the presence of anti-phospholipid antibodies and increased plasma levels of homocysteine and coagulation factor VIII.

More than fifty percent of thrombotic events in patients with inherited thrombophilia occur in the setting of an acquired risk factor.

1. Suspect inherited thrombophilia
   1. Venous thrombophilia
      • A family history of VTE and VTE at a young age (<45 years)
      • Recurrent VTE
      • VTE following minimal or no provocation
      • VTE at an unusual site (upper extremity, mesenteric vein, cerebral vein)
      • Pulmonary Embolism (PE) without obvious etiology
      • Neonatal purpura fulminans
      • Warfarin-induced skin necrosis
   2. Arterial thrombophilia
      • Patients with unexpected/ unexplained arterial thrombotic events.

2. Suspect acquired hypercoagulability
These are patients with unprovoked venous or arterial thromboembolism in the absence of a known family history. Some of them may have both venous and arterial thrombotic events.

Laboratory Findings

The laboratory testing for VTE does not alter acute therapy decisions, so there is no urgency in obtaining thrombophilia tests for patients who present with an acute venous. These values may help in warfarin and/or heparin administration.

Suspected inherited thrombophilia
Testing for inherited thrombophilia should be performed for a limited purpose; it is not a routine analysis. The patients who have had one episode of VTE and have thrombophilia are only at a slight risk of recurrent events.

• Venous thrombophilia: The most common causes of inherited venous thrombophilia are the factor V Leiden and the prothrombin gene mutations. Elevated factor VIII coagulant activity is now accepted as an independent marker of increased risk for thrombosis (4).
  • First step tests:
    • Activated protein C resistance (APCR): functional assay
    • Prothrombin G20210A: genetic assay
    • Protein C activity: functional assay
    • Protein S activity functional assay
    • Antithrombin (AT) activity: functional assay
  • Second-tier tests:
    1. Factor V Leiden mutation (if APCR is abnormal): genetic assay
    2. Protein C antigen (if functional test is low)
    3. Protein S antigen (total and free) (if functional test is low)
    4. AT antigen (if functional test is low), except in DIC, heparin therapy, or liver disease: Immunologic assays are rarely necessary
  • Third-tier tests:
    1. Thrombin time and fibrinogen for dysfibrinogenemia
    2. Factor VIII coagulant
    3. Other selected clotting factors (fibrinogen, factors VII, IX, vWF) to assess marked elevations—but studies are not well documented.

(ECL Note: ECL series has Erba Factor VIII deficient plasma (EHL00033) (For Factor VIII estimation) and Erba Factor IX deficient plasma (EHL00033) (For Factor IX estimation). These assays can be calibrated by using Erba Standard Plasma (EHL00012). Whereas, Erba Control N Plus (EHL00016) and Erba Control P Plus (EHL00017) can be used for quality control of these assays. Also, Erba Chrome Protein C (EH00009) and Erba Erba Protein S Clotting (EH00010) kits are available for Protein C and S activity assay.)

• Arterial thrombophilia
  • Lipid profile
  • Lipoprotein (a)
  • Homocysteine 

Suspected acquired hypercoagulability:

1. First-level tests:
   • Lupus anticoagulant
   • Anticardiolipin and anti-β2 glycoprotein 1 antibodies (IgG and IgM)
   • Antinuclear antibodies (ANA)
   • DIC (recommended DIC panel: FDP, Latex D-dimer, antithrombin)
   • Heparin-induced thrombocytopenia (HIT) must be ruled out DVT/PE: an ELISA-sensitive, quantitative assay for D-dimers to be used in relation with a probability algorithm
   • Lipid profile
   • Homocysteine
2. Second-level tests:
   • Comprehensive investigation of possible underlying neoplasm or a myeloproliferative disorder, including JAK-2 mutation.
   • Paroxysmal nocturnal hemoglobinuria (PNH)–flow cytometry4.

(ECL Note: ECL series has Erba D Dimer R (EHL00011 & EH00028) (For D Dimer). These assays can be calibrated by using Erba D Dimer Calibrator (EHL00018) and Erba D Dimer Control N+P (EHL00019).
ECL series has Erba LA1 screen (EH00037) & Erba LA2 confirm (EHL00038) for Lupus Anticoagulant assay.)

References

1. ISTH Steering Committee for World Thrombosis Day. Thrombosis: a major contributor to the global disease burden. J Thromb Haemost 2014; 12: 1580–90
2. Maurizio Zangari; Thrombophilia; Drug Target Insights 2008:3 87–97
3. Sandra Margeti; laboratory investigation of thrombophilia; J Med Biochem 33: 28–46, 2014
4. Mary Williamson. L. Micheal Snyder; Interpretation of Diagnostic Tests, Tenth Edition. Wolters Kluwer.