1. Chapter 17 Coagulation Testing
Hemostasis Unit 3
Chapter 17
Coagulation Testing
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2. Coagulation Tests Evaluate specific phases of the coagulation process
Some require specialized instruments
Preferred over manual due to variability of manual tests
Tests may be altered if platelet count is low
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3. Coagulation Tests (cont.)
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4. Buccal Mucosa Bleeding Time
Primary assay for detection of abnormalities in platelet function
Supplies
Spring-loaded lancet
Blotting paper or filter paper
Stopwatch
Tourniquet
Sedated or anesthetized patient – lateral recumbency
Buccal
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5. Buccal Mucosa Bleeding Time (cont.)
Gauze to tie upper lip back and act as a tourniquet
Make a 1-mm-deep incision
Blot incision site every 5 seconds until bleeding has stopped
Normal 1 to 5 minutes
Prolonged bleeding indicates platelet dysfunction
Deficiencies in von Willebrand factor
Thrombocytopenia
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6. Activated Clotting Time
Can evaluate every clinically significant clotting factor except Factor VII
Manual method
Vacutainer containing diatomaceous earth or kaolin that triggers the coagulation pathways
Prewarm tube to 37° C
Collect 2 mL via venipuncture
Timed from collection to presence of clot
Observed at 60 seconds then every 5 seconds until clotted
Normal 60 to 90 seconds
Automated analyzers are available
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7. Automated ACT Analyzer
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8. Whole Blood Clotting Time
Lee-White method
Older test not commonly performed
Activated clotting tests are more sensitive
3 mL of blood in plastic syringe
Timed from first collected
Place immediately into each of 3, 10 × 75-mm tubes rinsed with saline
Place in water bath (37° C)
Measure clotting time from collection to clot formation in third tube
Normal – dogs 1 to 10 minutes, horses 4 to 15 minutes, cattle 10 to 15 minutes
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9. Activated Partial Thromboplastin Time (aPTT)
Evaluates intrinsic and common clotting mechanisms
Coag DX™ analyzer
Handheld analyzer
Prothrombin time
aPTT
A variety of disorders and addition of heparin can affect results
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10. Prothrombin Time Test Or one stage prothrombin time (OSPT)
Usually performed on automated analyzers
Evaluates intrinsic and common coagulation pathways
Normal, dogs 7 to 10 seconds
Prolonged time indicates
Severe liver disease
DIC
Hereditary or acquired deficiencies of any factors
Vitamin K
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11. Clot Retraction Test
Evaluates plate number and function and the intrinsic and extrinsic pathways
Draw blood into a plain sterile tube and incubate at 37° C
Examine tube at 60 minutes and periodically over a 24-hour period
Clot should be evident in 60 minutes and retracted in approximately 4 hours with marked retraction at 24 hours
Does not provide information about source of coagulopathy
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12. Fibrinogen Determination
Automated methods not commonly performed in hospital
Manual
Two hematocrit tubes centrifuged for PCV
Determine total solids in one tube
Incubate other at 58° C for 3 minutes
Recentrifuge and measure total solids
Multiply the total solids by 1000 to obtain the concentration in milligrams/deciliter
TS mg/dL (nonincubated) – TS mg/dL (incubated) =
fibrinogen mg/dL
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13. PIVKA Proteins induced by vitamin K absence
Vitamin K is required to activate coagulation Factors II, VII, IX, and X
When vitamin K is deficient, precursor protein of those factors build up and can be detected by PIVKA
Slightly more sensitive than prothrombin
May be prolonged within 6 hours of ingestion of rodenticides
24 hours for prothrombin
48 hours for partial thromboplastin time
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14. D-Dimer and Fibrin Degradation Products
Evaluate tertiary hemostasis or fibrinolysis
Products formed as clot is degraded
Useful in identifying
DIC
Liver failure
Trauma
Hemangiosarcoma
In-house test for d-Dimer analysis
Immunoassays
More specific then FDPs, as FDPs can be formed before a clot forms
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15. von Willebrand Factor vWF required for platelet adhesion
Performed when platelet function defects are evident
Immunoassays in reference laboratories
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16. Coagulation Factor Assays
Performed in reference laboratories
Occur due to and may alter clotting factors:
Hereditary conditions
Acquired conditions
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17. Summary
Coagulation tests evaluate specific parts of the coagulation pathways
Most assays are performed on automated analyzers
Buccal mucosa bleeding time provides an evaluation of platelet number and function
Coagulation factor assays are performed in reference laboratories
Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.