coagulation 1

7/30/2019 Coagulation 1

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M.R.T. 4DMT

COAGULATIONHemostasis

- cellular and biochemical events which function in harmony to keep blood with the veins andarteries.

- prevent blood loss from injuries.

- re-establish blood flow.

1. Primary Hemostasis

- involves platelets and endothelium.- activated by small injuries.

- rapid, short-lived reponse.

- positive feedback: formation of platelet plug.

A. Platelets

Production:Hemocytoblast Megakaryoblast Promegakaryocyte

Megakaryocyte Metamegakaryocyte Platelets

Distribution:

a. Peripheral blood 70%

b. Spleen 30%

RR: 150 400 x 10^9 / L

Life Span: 8 11 days

Size: 2.5 m in diameter

Zones:

a. Peripheral zone adhesion and aggregation.b. Sol Gel zone shape and contraction.c. Organelle zone metabolic activities.

Function:

a. Adhesion -platelets roll and cling to non - platelet surfaces.

b. Activation - occurs when vWF and collagen binds to glycoprotein Ib receptoron the surface of the platelet.

c. Aggregation -platelets adhere to each other.

d. Secretion -platelets discharge the contents of their granules.e. Clot Retraction creates more bulk in the clot making it more resistant to

stress.

f. Cytokine signalling -platelets secrete platelet derived growth factor.

B. Endothelial cells

- assist in platelet activation.- limits coagulation mechanism.

- clot dissolution.


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2. Secondary Hemostasis

- involve coagulation factors.- activated by large wounds from trauma, surgery, dental procedures.

- delayed, long-term response.

- positive feedback: formation of fibrin clot.

A. Coagulation

- mechanism whereby after injury to a blood vessel, plasma coagulation factors, tissue factors,and calcium work together on the surface of platelets to form a fibrin clot.

B. Coagulation Factors

- proteins engaged in formation of a fibrin clot from fibrinogen.

Factor Customary name FunctionI Fibrinogen Thrombin substrate, polymerizes to form

fibrin

II Prothrombin Serine protease

III Tissue factor Cofactor

IV Ionic Calcium Mineral

V Labile factor Cofactor

VII Stable Factor Serine protease

VIII Antihemophilic Factor

(vWF)

Cofactor

Factor VIII carrier and platelet adhesion

IX Christmas factor Serine protease

X Stuart-Prower factor Serine protease

XI Plasma thromboplastin antecedent

(PTA)

Serine protease

XII Hageman factor Serine protease

Prekallikrein Fletcher factor, PK Serine protease

High Molecular Weight

Kininogen

Fitzgerald factor, HMWK Cofactor

XIII Fibrin-stabilizing factor (FSF) Transamidase

Platelet factor 3 Phospholipids, phosphatidyl serine

PF3

Assembly molecule

C. Coagulation Cascade

- series of biochemical reactions and feedback mechanisms by means of intrinsic and extrinsic

pathway, or both, leading to a common pathway forming a fibrin clot.

C.1. Intrinsic pathway

- utilization of plasma contact factors to initiate coagulation, beginning with theactivation of factor XII; all necessary factors required are contained in the circulating

blood.

- activated partial thromboplastin time (aPTT) test monitors this pathway.


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- aPTT measures factors XII, XI, X, IX, VIII, V, II and I.

C.2. Extrinsic pathway

- coagulation pathway that is activated by tissue thromboplastin; necessary components

are factor VII and calcium.- prothrombin time (PT) test monitors this pathway.

- PT measures factors VII, X, V, II, I.

C.3. Common pathway

- final stage of the coagulation cascade, beginning with the convergence of the extrinsic

and intrinsic pathways (factor X) ending with the formation of fibrin clot.


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3. Specimen Collection and Handling

A. Anticoagulants

- 3. 8 % or 3.2 % sodium citrate- normal ratio of blood to anticoagulant is 9:1

B. Holding sample

- siliconized glassware (glass activates factor XII and platelets will adhere to glass).

C. Collection of Blood Sample

- venipuncture should be clean and quick with minimal stasis.

- if drawing tubes for other tests, draw blue top last, except that if an EDTA tube is needed for a

CBC, the purple top tube should be drawn after the blue top coagulation tube. If only drawingblood for coagulation testing, allow some blood to drip into vacutainer before collection. (The first

blood drawn in a venipuncture is most likely to be contaminated with small amounts of tissue

thromboplastin. This can activate the extrinsic pathway and lead to variable results).- prompt and gentle inversion must be done to bind all calcium immediately.

D. Specimen Processing

- transportation to the laboratory should be done as quickly because some changes can begin in vitro.

- specimens should be centrifuged for 10 minutes to get the cell - free plasma - anticoagulant

mixture.

- always check for micro-clot formation, if present, specimen is unacceptable for testing.- hemolyzed specimens are also unacceptable for testing because of possible clotting factor

activation.

4. Routine Test of Hemostatic Function

A. Primary Hemostasis

A.1. Bleeding Time

- measures the time required for the cessation of bleeding after a standardized capillarypuncture to a capillary bed.

- the time required will depend on the capillary integrity, number of platelets and the

platelet function.

- types:a. Duke method: earlobe; RR: 0-6 minutes.

b. Ivy method: forearm; RR: 1-6 minutes.

c. Template method: forearm; RR: 2-9.5 minutes.

- prolonged with aspirin.


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A.2. Clot Retraction

- evaluates platelet function, fibrinogen, red cell volume and fibrinolytic activity.

- whole blood is allowed to clot and observed for retraction.

- platelets of adequate number and viability are required for clot retraction to occur.

- normal value: evidence of retraction within 2 hours (varies with methodology).

B. Secondary Hemostasis

B.1. Coagulation time/ Clotting Time

- measures the period required for the free flowing blood to clot or solidify after it has

been removed to the body.- types:

a. Drop or Slide method: capillary blood; NV: 2-4 minutes

b. Lee and White method (tube method): venous blood: NV: 7-15 minutes

B.2. Prothrombin Time (PT)

- test for extrinsic and common pathway.

- measures factors I, II, V, VII and X.- monitors oral anticoagulants (warfarin, coumarin, dicoumarol).

- reagent: tissue thromboplastin and CaCl2.- sensitive to vitamin K factors.- International normalized ratio (INR)

INR = (patient result)ISI

(mean of the reference range)

*ISI = International Sensitivity Index from manufacturer

- reference range: < 14 secondsa. Therapeutic goal: INR 2.0 3.5

B.3. Activated Partial Thromboplastin Time

- test for intrinsic and common pathway.

- measures all factors except factor VII and XII.

- monitors heparin therapy.

- reagents: activator (kaolin, celite or ellagic acid), platelet phospholipid (PF3) and CaCl2.

- reference range: 20 40 seconds


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OTHER TESTS:

Laboratory Tests for Primary

Hemostasis

Laboratory Tests for Secondary

Hemostasis

Laboratory Tests for

Fibrinolysis

1. Capillary Resistance /Fragility/ Tourniquet

/Rumpel Leedes or HessTest

2. Platelet Adhesiveness Test3. Platelet Aggregation Test

4. Platelet Count

5. Platelet Morphology andMPV

1. Plasma Recalcification Time2. Activated Clotting Time

3. Stypven Time4. Thrombin Time / Thrombin

Clotting Time

5. Reptilase Time6. Substitution Test (Mixing

Studies)

7. ProthrombinConsumption/Serum

Prothrombin Test

8. Thromboplastin GenerationTest

9. Specific Factor Assay

10. Assay of vWR:Ag and

vWR:Reo Rockett/Laurel11. Duckerts or Clot Solubility

Test

12. Tests for Circulating Inhibitorsof Coagulation

1. Determination ofFibrinolytic Products

2. Lysis Time3. Proteins involved in

Fibrinolysis

5. Bleeding Disorders


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Disorder of Primar Hemostasis

Vascular Disorde

Acquire

Anaphylact

purpura,Henoch

Schonlein,Senile purp

Scurvy, Pur

simplex,Infectious

purpura, Dr

induced

purpurasassociated w

paraprotene

s, Amyloid

Idiopathic

purpuras

Hereditary

Hereditary

Hemorrhagic

Telangiectasia/

Rendu-Weber-

Osler,Hemangioma-Thrombocytopenia

Kasabach-Merit,

Ehler-Danlos,Marfan,

Osteogenesis

imperfect,

Pseudoxanthoma

elasticum

Platelet Disorders

Qualitative Quantitative

Thrombocytosis

primary

reactive

Thrombocytopenia

Disorders relatedto distribution or

dilution /big

spleen

Increased platelet

destruction/ utilization

TTP, drug induced,

non immunemechanisms, DIC

Impaired/

decreased

platelet

production BM failure

Congenital hypoplasia, MHA,

WAS, BS, Fanconi, TAR

Neonatal hypoplasia

- drugs, infections

Acquired hypoplasia -ionizing radiation, drugs

Disorders of Platelet Secretion

Disorders

of Platelet

AdhesionDisorders of

PlateletAggregation

Glanzmanns

thrombasthenia

Acquired von

WillebrandDisease

Bernard

Soullier/

Giant

PlateletSyndrome

vonWillebrand

Disease

Thromboxane

Pathway Disorders

AcquiredHereditary

aspirin like

defects due to inhibitors of

prostaglandin pathway(chronic aspirin intake or

inhibitors of

thromboxane or cyclo-

oxegenase pathway

Storage Pool

Diseases

Primary granuledeficiency

Hemmeler

anomalyElectron dense/delta granules

deficiency

Pudlak,

WiskottAldrich,

Chediak

Higashi,

TAR Alpha granules deficiency

Gray Platelet Syndrome,

Quebec Platelet Disorder


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References:

McPherson, R. & Pincus, M. (2006). Henrys Clinical Diagnosis and Management by Laboratory Methods. US: SaundersElsevier

Linne, J. & Ringsrud, K. (1999). Clinical Laboratory Science The Basics and Routine Techniques

Harmening DM: Clinical Hematology and Fundamentals of Hemostasis, ed 3. Philadelphia, FA Davis Co, 1997.

Turgeon ML: Clinical Hematology: Theory and Procedures, ed 3. Philadelphia, Lippincott-Raven Publishers, 1998.


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