Clotting, Hemostasis, Clotting, Hemostasis, AnticoagulationAnticoagulation

Doç.Dr.Jale Çoban

Topics

1- Hemostasis overview

2- Coagulation

3- Bleeding / thrombosis

4- Laboratory tests

5- Patient samples

Hemostasis

The balance between clotting and bleeding

Components of Hemostasis:– Vasculature– Coagulation proteins– Platelets

Clot Formation Clot Dissolution

Hemostasis („hemo”=blood; sta=„remain”) is the stoppage of bleeding, which is vitally important when blood vessels are damaged.

Following an injury to blood vessels several actions may help prevent blood loss, including:

Formation of a clot

PHASES OF THE HEMOSTATIC PROCESS

• Initiation and formation of the platelet plug • Propagation of the clotting process by the

coagulation cascade• Termination of clotting by antithrombotic

control mechanisms• Removal of the clot by fibrinolysis

Local vasoconstriction• is due to local spasm of the

smooth muscle (symp. reflex)

• PLT comming in contact with exposed collagen release: serotonin, ADP, TXA2, which accelerate vasoconstriction and causes PLT to swell and become more sticky

Formation of a platelet plug. When blood platelets adhere to collagen in the wall of a defective blood vessel, they release ADP and synthesize thromboxane A2. These substances increase the adhesiveness of the platelets,

causing more platelets to aggregate at the site of injury.

The functional response of activated platelets involves four different processes:

1. Adhesion — the deposition of platelets on the subendothelial matrix

2. Aggregation — platelet-platelet cohesion3. Secretion — the release of platelet granule

proteins4. Procoagulant activity — the enhancement of

thrombin generation

• This process is facilitated by a plasma glycoprotein, von Willebrand factor (vWF). Produced in both endothelial cells and platelets, vWF forms bridges between receptors on the surface of platelets and collagen fibers in the connective tissue.

Formation of platelet aggregate

• Injured blood vessel releases ADP, which attracts platelets (PLT)

• PLT comming in contact with exposed collagen release: serotonin, ADP, TXA2, which accelerate vasoconstriction and causes PLT to swell and become more sticky

Formation of blood clot

• In the formation of the clot, an enzyme called thrombin converts fibrinogen into insoluble protein, fibrin

• Fibrin aggregates to form a meshlike network at the site of vascular damage

CLOTTING CASCADE AND PROPAGATION OF THE CLOT

The clotting cascade is depicted as consisting of an intrinsic and extrinsic pathway .

Extrinsic pathway:

1. When blood comes in contact with injured tissue – tissue thromboplastin (F III) interacts with (F VII), and Ca2+ activating (F X).

Stage I: Formation of prothrombin

activator

Ca2+

Stuart factor

Anti- hemophilic factor

Christmas factor

Intrinsic pathway:

2. Exposed collagen activates (F XII). Activated F XII activates plasma enzyme – plasma thromboplastin antecedent (PTA; F XI, which in the presence of Ca 2+ activates (F IX). F IX interacts with (F VIII), Ca 2+ to form a complex that activates (F X).

Stage I: Formation of prothrombin

activator

Ca2+

Christmas factor

Anti- hemophilic factor

Stuart factor

Stage I: Formation of prothrombin

activator

3. Common pathway:

Activated F X in the presence of Ca 2+ forms complexes with accelerin (F V) to form prothrombin activator

Ca2+

Christmas factor

Anti- hemophilic factor

Stage II: conversion of prothrombin to thrombin

• Prothrombin – inactive precursor of enzyme thrombin• In the presence of prothrombin activator and Ca2+

prothrombin is converted to thrombin• Thrombin itself increases its own rate of formation

(positive feedback mechanism)

Ca2+

Stage III: conversion of fibrinogen to fibrin

• Fibrinogen – plasma protein produced by the liver• Thrombin converts fibrinogen to fibrin• Thrombin also activates fibrin-stabilizing factor (F XIII),

which in the presence of Ca2+, stabilizes the fibrin polymer through covalent bonding of fibrin monomers

fibrin-stabilizing factor

Calcium ions

• Are required for promotion and acceleration of almost all blood clotting reactions

• Except: activation of XII and XI (intrinsic mechanism)

Ca2+

Fibrinolysis

Clot Dissolution1. Plasmin is formed from plasminogen - enzyme called

activator (e.g. enzymes from urine, tears, saliva or bacterial enzyme streptokinase)

2. Plasmin as an enzyme is involved in breaking down fibrin into soluble fragments (fibrinolysis)

Plasminogen PlasminPlasmin

t-PA

Fibrin soluble fragments

Anticoagulants

Hirudo medicinalis produce

Hirudin that inhibits Thrombin

Anticoagulants

• Although tissue breakdown and platelets destruction are normal events in the absence of trauma, intravascular clotting does not usually occur because:- the amounts of procoagulants released are

very small- natural anticoagulants are present

(Antithrombin III, Heparin, Antithromboplastin, Protein C and S, fibrin fibers)

Natural anticoagulants• Antithrombin III – inhibits factor X and thrombin

• Heparin from basophils and mast cells potentiates effects of antithrombin III (together they inhibit IX, X, XI, XII and thrombin)

• Antithromboplastin (inhibits „tissue factors” – tissue thromboplastins)

• Protein C and S – activated by thrombin; degrade factor Va and VIIIa

Thrombocytopenia

Severe reduction in the number of PLTs - thrombocytopenia

this causes spontaneous bleeding as a reaction to minor trauma

in the skin - reddish-purple blotchy rash

it may result from:- decreased production

(toxins, radiation, infection, leukemias)

- increased destruction (autoimmune processes)

- increased PLTs consumption (DIC) Hemorrhagic spots (petechiae)

Hepatic failure

• Most of the clotting factors are formed in the liver

Subconjunctival hemorrhage

Disseminated intravascular coagulation (DIC)

• Widespread coagulation thrombosis in small blood vessels increased fibrinolysis, and depletion of coagulating factors generalized bleeding

• It may result from:- bacterial infections

(endothelial damage)- disseminated cancers

(release of procoagulants)- complications of pregnancy- severe catabolic states Disseminated cervical

cancer metastases (PET imaging)

Hemophilia A (lack of F VIII) and B (lack of F IX) are transmitted genetically and affect only males.

Females carry the gen but do not show symptoms.

Von Willebrand’s disease – loss of large component of fVIII

Hemophilia A (lack of F VIII; 85%)

• Spontaneous or traumatic subcutaneous bleeding

• Blood in the urine• Bleeding in the

mouth, lips, tongue• Bleeding to the

joints, CNS, gastrointestinal tract

Mild hemophilia after injection in buttock

Tests of coagulation

LABORATORY EVALUATION

PLATELET COUNT BLEEDING TIME (BT) PROTHROMBIN TIME (PTT) PARTIAL THROMBOPLASTIN TIME (aPTT) THROMBIN TIME (TT)

PLATELET COUNT NORMAL 150,000 - 400,000 CELLS/MM3

< 100,000 Thrombocytopenia

50,000 - 100,000 Mild thrombocytopenia

< 50,000 Sev Thrombocytopenia

Bleeding time

• The blleding time is intennded to measure platele function, but it is neither a sensitive nor a spesific test.

• Platelet counts < 100.000/uL, aspirin, other platelet inhibitory drugs can prolong the bleeding time

• Tne bleeding time can be prolonged in von Willebrand disease and other hereditary plateled function disorders.

Bleeding time – procedure:

• A trained healtcare professionall makes a small incision on the patient’s arm, and every 30 sec. Gently blots the blood with filtter paper to see if the bleeding has stopped.The filter paper must not touch the wound.Prior to making the cut, a blood pressure cuff is placed on the patient’s arm at 40 mmHg.

• Referance İnterval :

1 - 9min.

This may vary from lab to lab, depending on how the test is measured

Whole blood clotting time

The time taken for blood to clot mainly reflects the time required for the generation of thrombin

The surface of the glass tube initiates the clotting process. This test is sensitive to the factors involved in the intrinsic pathway

The expected range for clotting time is 4-10 4-10 mins.mins.

Whole blood clotting time – procedure:

• Clean the tip of the finger with an alcohol • Prick the finger tip with an automatic lancet • Note the time when blood first appears on

the skin • Touch the tube to the drop of blood • Break gently 1cm of the tube at the end of 2

min, and every 30 sec these after • When fibrin is formed between the two

broken pieces of tube the coagulation or clotting time is noted

"Intrinsic" and "extrinsic" coagulation pathways

Activated Partial Thromboplastin Time

N: 25-35 sec

Prothrombin Time: 12 – 14 sec

• The intrinsic pathway is initiated by the exposure of blood to a negatively charged surface (such as celite, kaolin, or silica in the in vitro activated partial thromboplastin clotting time [aPTT]).

• The extrinsic pathway is activated by tissue factor exposed at the site of injury or tissue factor-like material (thromboplastin, TPL in the in vitro prothrombin clotting time [PT]).

Protrombin Time (PTT)• The PT measures the clotting time from

factor VII through fibrin formation(extrinsic and common pathways).

• PT prolangations caused by: 1.factor deficiencies involoving -fibrinogen

-factor II (protrombin) -factor V -factor VII -factor X2.therapeutic anticoagulans Warfarin (Coumadine)3. Lupus anticoagulants or by spesific factor inhibitors against

Fibrinogen or factor II,V,VII or X

Protrombin Time (PTT)• PT reagents is called thromboplastin (phospholipid with

tissue factor and Ca++). It is added to patient plasma, and the time until clot formation is measured in seconds(Referans interval: 12-14 sec).

• Tissue factor activates the extrinsic pathway.Phospholipid and Ca++ are required cofactors in the coagulation cascade.

• Citrate in the blue top tube prevents clotting by chelating Ca++

• Prolonged PT:- a vitamin K deficiency (vitamin K is a co-factor in the synthesis of

functional factors II prothrombin), VII, IX and X)- liver disease- Warfarin therapy (Coumadin)

Monitoring Warfarin (coumadin)

• Warfarin is monitored by the international normalized ratio (INR)

• The usual therapeutical goal is an INR of 2-3.

International Normalised Ratio (INR)

• INR is calculated from the PT and is intended to allow valid comparisons of results regardless of the type of PT reagent used among different laboratories:

INR=(patient PT / mean normal PT)ısı

• International sensitivity index(ısı) is a measure of the sensitivity of a particular PT reagent. Different PT reagents have different sensitivities to factor deficiencies.

• A patient’s prothrombin time (PT) test result expressed as a ratio to a normal population control which has been standardized (or normalized) for the potency to the thromboplastin used in the assay.

• It is standardized using a World Health Organization (WHO) international reference thromboplastin preparation, and determined using the equation:

INR = R^ISI,

where R is the PT ratio obtained with the working thromboplastin.

International Normalised Ratio (INR)

• The result for the PT is expressed as a ratio (prothrombin clotting time for patient plasma divided by time for control plasma);

• Correction factor (International Sensitivity Index) is applied to the prothrombin ratio and the result issued as INR.

• Therapeutic interval: Therapeutic interval for oral anticoagulant therapy: 2.0-4.5.

• Application: Monitoring oral anticoagulant therapy (eg. Warfarin);

• note that heparin will not prolong INR (heparinase is included within the INR reagent)!!!!!!!!!!!!! For heparin therapy we monitor aPTT and/or aPTT ratio

Activated Partial Thromboplastin Time (aPTT)

• aPTT measures the cloting time from the activation of factor XII,through the formation of fibrin clot (intrinsic and common pathways)

• aPTT prolangations are caused by:1. Either factor deficiencies (especially

of factors VIII,IX,XI and/or XII)2. Monitor therapeutic anticoagulan

HEPARİN

Activated Partial Thromboplastin Time (aPTT)

PTT reagent(phospholipid with an intrensic pathway activator such as silica, kaolin...) and Ca++ are added to patient plasma, and the time until clot formation is measured in second.

• prolongation of both the APTT and PT suggests factor X, V, II or I (fibrinogen) deficiency, all of which are rare

• aPTT is normal in factor VII deficiency (PT prolonged) and factor XIII deficiency

Most common case of prolonged aPTT – heparin!!!Most common case of prolonged aPTT – heparin!!!

Role of PT, PTT:Role of PT, PTT:Warfarin, Heparin MonitoringWarfarin, Heparin Monitoring

Anticoagulant PT aPTT

Heparin Normal Prolonged

Warfarin (Coumadin)

Prolonged Normal

Hp F %0 Np F %100

Mixing TEST

Mix F %50

Hp aPTT 70 sn

Hp aPTT 32 sn

+

+

+ Mix 32 sn

Thrombin time (TT) – norm: 14-15 sec

Prolonged TT:• Heparin (much more sensitive to heparin

than aPTT)• Hypofibrinogenemia

Selected causes of abnormal coagulation tests

Partial Thromboplastin

Time (aPTT)

Prothrombin Time (PT)

Thrombin Time (TT)

Bleeding Time (BT)

Factor deficiency (except VII)

VII, X, V, II, fibrinogen deficiency

Low or absent fibrinogen

Thrombocytopenia

Antibodies to clotting factors

Antibodies Dysfibrinogenemia, hypofibrinogenemia

Von Willebrand’s disease

Heparin Warfarin; Vit K defficiency (mild to severe)

Heparin Drugs (Aspirin, NSAIDs, high dose penicillins, etc.)

Excessive Warfarin Excessive Heparin Cirrhosis, Uremia, PLTs dysfunction

AnticoagulantsAnticoagulants

• Heparin• Warfarin (Coumadin)• Direct thrombin inhibitors• Antiplatelet agents