Tabuk University

Faculty of Applied Medical SciencesDepartment Of Medical Lab. Technology

3rd Year – Level 5 – AY 1434-1435

1

HEMATOLOGY – 2, MLT 307

Thrombotic disorders

By/Dr. Walid ZAMMITI; Phd

M.Sc; MLT

Objectives

• Define terms used in thrombotic disorders.• Identify the most common causes for thrombosis.• Classify thrombosis into arterial and venous; and the differences between them.• Classify thrombotic disorders into hereditary and acquired.• Understand the mechanism of thrombosis in specific hereditary & acquired

conditions.• Learn the diagnostic tests used to identify genetic predisposition to thrombosis.

Disease processes

Abnormal clotting Abnormal bleeding

Bleeding disorders : caused by Platelets, vascular, coagulation factors

Thrombotic disorders

Thrombosis

• Thrombus: singular , Thrombi : Plural• Thrombi are solid masses or plugs formed in the circulation from blood

constituents. • Platelets and fibrin form the basic structure. Their clinical significance results

from ischaemia from local vascular obstruction or distant embolization. • Thrombi are involved in the pathogenesis of myocardial infarction,

cerebrovascular disease, peripheral arterial disease and deep vein occlusion.

• Thrombosis may be arterial, causing ischemia, or venous leading to stasis .• Thrombosis, both arterial and venous, is more common as age increases and is

frequently associated with risk factors. The term thrombophilia is used to describe the inherited or acquired disorders of the haemostatic mechanism that predispose to thrombosis.

Arterial thrombosis

• Atherosclerosis الشرايين ,of the arterial wallتصلبplaque rupture and endothelial injury expose blood to subendothelial collagen and tissue factor. This initiates the formation of a platelet plugs on which platelets adhere and aggregate.

Venous thrombosis• It is suggested that there are three components that

are important in thrombus formation:1. Slowing down of blood flow;2 .Hypercoagulability of the blood; and3 .Vessel wall damage.• Increased systemic coagulability and stasis are most important, vessel

wall damage being less important than in arterial thrombosis

Thrombotic disorders

• Hereditary-Factor V Leiden gene mutation (activated protein C resistance)- Antithrombin deficiency- Protein C deficiency- Protein S deficiency- Prothrombin allele G20210A- Hyperhomocyst(e)inaemia- Defects of fibrinogen

• Acquired– Post surgery– Post delivery– Long distance travel– Immobilization– Malignancy– Inflammation– Blood disorders– Oestrogen therapy– The antiphospholipid syndrome– Factor IX concentrates

Activated Protein C (APC) Resistance(Factor V Leiden mutation)

• Genetic alterations of the factor V molecule at APC binding sites impair, or resist APC’s ability to degrade or inactivate factor Va.

• Site of mutation is replacement of arginine at position 506 with glutamine (Arg506Gln) in the factor V gene.

• It is the most common inherited cause of increased risk of venous thrombosis.

• It doesn’t increase risk of arterial thrombosis• Diagnosed by PCR : Polymerase Chain Reaction.

Antithrombin

• Also known as Antithrombin III• Antithrombin forms "complexes" with all the serine protease

coagulation factors except factor VII, this "kills" the enzyme.

Prothrombin Thrombin

ATIII inhibits thrombin to prevent thrombus formation

Antithrombin III

Fibrinogen

Fibrin

“Thrombus”

Antithrombin deficiency

• There are recurrent venous thromboses usually starting in early adult life. Arterial thrombi occur occasionally.

Protein C & S

Protein C andProtein C Deficiency

• Protein C is a vitamin K dependent glycoprotein produced in the liver• In the activation of protein C, thrombin binds to thrombomodulin, a structural

protein on the endothelial cell surface• This complex then converts protein C to activated protein C (APC), which degrades

factors Va and VIIIa, limiting thrombin production• For protein C to bind, cleave and degrade factors Va and VIIIa, protein S must be

available• Protein C deficiency, whether inherited or acquired, may cause thrombosis when

levels drop to 50% or below• Protein C deficiency occurs with surgery, trauma, pregnancy, liver or renal failure or

DIC.

Protein S, Protein S Deficiency

• Protein S is an essential cofactor in the protein C pathway• Protein S exists in a free and bound state• About 30% of unbound protein S, called free PS, is the

functionally active form of protein S• Inherited PS deficiency is an autosomal dominant disorder,

causing thrombosis when levels drop to 50% or lower

Causes of Acquired Protein S Deficiency

Decreased PS Functional activity may be due to :1. vitamin K deficiency 2. liver disease 3. Due to increased PS consumption which occurs in acute

thrombosis, DIC, MPD, sickle cell disease

Prothrombin gene mutation

• Prothrombin allele G20210A is a variant (prevalence 2-3% in the population) that leads to increased plasma prothrombin levels and increases thrombotic risk by at least twofold.

Acquired risk factors of thrombosis

- Post surgery: elderly, obese & those with family history.

- Venous stasis and Immobilization : probably responsible for the highincidence of postoperative venous thrombosis.

- Malignancy : carcinoma of the ovary, brain and pancreas have a particularly increased risk of venous thrombosis but there is an increased risk with all cancers.

- Inflammation : down regulates anticoagulant pathways, particularly proteinC.

- Blood disorders :In polycythaemia vera and essential thrombocythaemia; there are Increased viscosity, thrombocytosis, altered platelet membrane receptors and responses.

Antiphospolipid syndrome

• Def: occurrence of thrombosis or miscarriage in association with antiphspholipid antibodies.

* Antiphospholipid antibodies may be:• Lupus anticoagulant (LA); causing prolonged APTT not

corrected by mixing with normal plasma.• Anticardiolipin antibodies (ACA).

Antiphospholipid Syndrome : Diagnosis

• Clinical association of (APA):-Arterial or venous thrombosis-Pregnancy loss

-Thrombocytopenia -CNS stroke• Laboratory Criteria

-IgG or IgM anticardiolipin antibody-medium or high titer.

-Detected in an ELISA assay

Oestrogen therapy

• Oestrogen therapy, particularly high-dose therapy, is associated with Increased plasma levels of factors II, VII, VIII, IX and X and,

• Depressed levels of antithrombin and tissue plasminogen activator in the vessel wall.

Investigation of thrombophilia• Screening tests:- Blood count and erythrocyte sedimentation rate (ESR)- Blood film examination- Prothrombin time (PT) and APTT : (a shortened APPT is often seen in

thrombotic states and may indicate the presence of activated clotting factors. A prolonged APTT test, not corrected by the addition of normal plasma, suggests a 'lupus anticoagulant‘ or an acquired inhibitor to a coagulation factor.)

- Anticardiolipin and anti-β2-GPI antibodies- Thrombin time and reptilase time: (prolongation suggests an

abnormal fibrinogen)

- Fibrinogen assay.- Activated protein C (APC) resistance test and DNA analysis for factor V Leiden.- Antithrombin-immunological and functional assays.- Protein C and protein S-immunological and functional assays.- Prothrombin gene analysis for the G20210A variant.- Plasma homocysteine estimation- Test for CD59 and CD55 expression (PNH) in red cells. (if

paroxysmalnocturnal haemoglobinuria is suspected.)

Anticoagulant drugs

• Anticoagulant drugs are used widely in the treatment of venous thromboembolic disease. Their value in the treatment of arterial thrombosis is less well established.

• Heparin: laboratory controlled using APTT mainly.• Oral anticoagulants : e.g : Warfarin, laboratory controlled using

PT & INR (International Normalized Ratio).

THANK you