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Hematology: Blood coagulation
- 1. 1 PROTÉGÉ EDUCATION CENTER,LLC Giving the Gift of Education www.ProtegeEducation.com Thank You for joining
- 2. Medical Laboratory Scientist Hematology Part 4of 4: Blood coagulation Brief overview 2Protégé Education Center, LLC All rights reserved www.ProtegeEducation.com Presented by Nithianandan Selliah, PhD Scientist Founder and CEO of Protégé Education Center, LLC
- 3. Protégé Education Center,LLC All rights reserved www.ProtegeEducation.com Hemostasis Normal hemostasis is the responsibility of a complex system of three individual components: Platelets - in the circulation Endothelial cells – line the wall of the blood vessel Blood-clotting proteins – circulate in the blood The process of hemostasis occurs in three phases: 1. Vascular platelet phase: primary hemostasis 2. Activation of the coagulation cascade: formation of the clot 3. Activation of a series of control mechanisms: stop the propagation of the clot and limit activation of the coagulation cascade to the region of endothelial rupture 3
- 4. Protégé Education Center,LLC All rights reserved www.ProtegeEducation.com Mechanisms of Blood Coagulation Primary hemostasis: 1. Vasoconstriction: When injury occurs, vessel walls constrict, causing reduced blood flow to the site of injury. 2. Platelet plug: Platelets aggregate to the site of the injury. They stick together acting as a "plug." Secondary hemostasis 3. Platelets activate the process which causes a fibrin clot to form. 4
- 5. Protégé Education Center,LLC All rights reserved www.ProtegeEducation.com Clotting Cascade Extrinsic Pathway The extrinsic pathway is activated by external trauma that causes blood to escape from the vascular system. This pathway is quicker than the intrinsic pathway. It involves factor VII. Intrinsic Pathway The intrinsic pathway is activated by trauma inside the vascular system, and is activated by platelets, exposed endothelium, chemicals, or collagen. This pathway is slower than the extrinsic pathway, but more important. It involves factors XII, XI, IX, VIII. Common Pathway Both pathways meet and finish the pathway of clot production in what is known as the common pathway. The common pathway involves factors I, II, V, and X. 5
- 6. Protégé Education Center,LLC All rights reserved www.ProtegeEducation.com Coagulation Cascade 6 Damaged vessel Intrinsic system Activated by chemicals, collagen, exposed endothelium, platelets Extrinsic system Blood escapes from vascular system Contact damaged tissues Release phospholipoproteins and organelle membrane Derives tissue thromboplastin or Tissue Factor Factor XII Factor XIIa XI XIa X IXa VIIIa PL Ca++ VIIa VIIIX Xa Prothrombin Thrombin XIII Fibrinogen Soluble fibrin monomer Ca++ VIIIa PL Ca++ Va PL Ca++ XIIIa Fibrin clot PL = Platelet Phospholipids
- 7. Protégé Education Center,LLC All rights reserved www.ProtegeEducation.com Activated Partial Thromboplastin Time (aPTT) aPTT measures the time necessary to generate fibrin from initiation of the intrinsic pathway. Activation of factor XII is accomplished with an external agent (e.g., kaolin) capable of activating factor XII without activating factor VII. The normal time is usually reported as less than 30 to 35 seconds (25 to 35 seconds), and decreased values ("short") may be abnormal. 7
- 8. Protégé Education Center,LLC All rights reserved www.ProtegeEducation.com Prothrombin Time (PT) PT measures the time necessary to generate fibrin after activation of factor VII. It measures the integrity of the "extrinsic" and "common" pathways (factors VII, V, X, prothrombin, and fibrinogen). A prolonged PT may reflect either factor deficiency or a circulating inhibitor of coagulation. The test is more sensitive than the aPTT for deficient levels of factors, and a relatively small drop in factor VII levels may prolong the PT. 8
- 9. Protégé Education Center,LLC All rights reserved www.ProtegeEducation.com Thrombin Time (TT) TT is the time to drive the reaction of fibrinogen to fibrin in the presence of thrombin It measures the integrity of this reaction and isolates an abnormality to either a decrease in normal fibrinogen or an inhibitor to its activation. Abnormalities can be: deficient fibrinogen (< 100 mg/dl), abnormal fibrinogen, or an inhibitor to the reaction. 9
- 10. Protégé Education Center,LLC All rights reserved www.ProtegeEducation.com Coagulation Cascade 10 Damaged vessel Intrinsic system Activated by chemicals, collagen, exposed endothelium, platelets Extrinsic system Blood escapes from vascular system Contact damaged tissues Release phospholipoproteins and organelle membrane Derives tissue thromboplastin or Tissue Factor Factor XII Factor XIIa XI XIa X IXa VIIIa PL Ca++ VIIa VIIIX Xa Prothrombin Thrombin XIII Fibrinogen Soluble fibrin monomer Ca++ VIIIa PL Ca++ Va PL Ca++ XIIIa Fibrin clot PL = Platelet Phospholipids aPTT PT TT
- 11. Protégé Education Center,LLC All rights reserved www.ProtegeEducation.com Antithrombin III Test This test is done if repeated blood clots oocur or if blood thinning medicine does not work. Lower-than-normal AT III can have an increased risk of clotting. Lower than normal AT III may be due to: Bone marrow transplant DIC (disseminated intravascular coagulation) AT III deficiency, an inherited condition causing lower blood clotting protein levels Liver cirrhosis Nephrotic syndrome Higher than normal AT III may be due to: Use of anabolic steroids 11
- 12. Protégé Education Center,LLC All rights reserved www.ProtegeEducation.com Factor VIII assay 12 This test is used to find the cause of too much bleeding (decreased blood clotting), or if a family member is known to have hemophilia A A normal value is 50 - 200% of the laboratory control or reference value. Decreased levels may be due to: Disseminated intravascular coagulation (DIC) Hemophilia A Presence of a Factor VIII inhibitor (antibody) Von Willebrand's disease Increased levels may be due to: Advanced age Diabetes Liver disease Inflammation Pregnancy Obesity
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Editor's Notes
- #8 The aPTT measures the time necessary to generate fibrin from initiation of the intrinsic pathway. Activation of factor XII is accomplished with an external agent (e.g., kaolin) capable of activating factor XII without activating factor VII. Citrated plasma, an activating agent, and phospholipid are added together and incubated at 37°C. Calcium is added, and the time necessary for the clumping of kaolin is measured. The normal time is usually reported as less than 30 to 35 seconds (25 to 35 seconds), and decreased values ("short") may be abnormal. This test is abnormal in the presence of reduced quantities of factors XII, IX, XI, VIII, X, V, prothrombin, and fibrinogen (all integral parts of the "intrinsic" and "common" pathway. It is usually prolonged if a patient has less than approximately 30% normal activity. It can also be abnormal in the presence of a circulating inhibitor to any of the intrinsic pathway factors. The differentiation of inhibitors from factor depletion is important and can best be accomplished by a mixing study in which patient and normal plasma are combined in a 1:1 ratio and the test is repeated on the mixed sample. If the abnormal value is corrected completely, the problem is factor deficiency. If the result does not change or the abnormality is corrected only partially, an inhibitor is present. This difference stems from the above mentioned fact that the aPTT will be normal in the presence of 50% normal activity Since platelet factors are necessary for the cascade to function normally, the test is performed in the presence of a phospholipid emulsion that takes the place of these factors. The classic partial thromboplastin time depends on contact with a glass tube for activation. Since this is considered a difficult variable to control, the "activated" test uses an external source of activation.
- #9 Inherited deficiency of factor VII is a rare bleeding disorder - a prolonged PT and a normal aPTT. The PT completely corrects when mixed with normal plasma. Acquired deficiencies are usually related to liver disease, warfarin therapy, or depletion secondary to consumptive coagulopathy, severe bleeding, or massive transfusion. Circulating inhibitors are most often directed at factor X or thrombin. Most common are heparin or products of fibrinolysis. In their presence the prolonged PT cannot be completely corrected to normal in a 1:1 mixing study.
- #10 Afibrinogenemia- abnormal fibrinogen – dysfibrinogenemia consumptive coagulopathies
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