Chapter 17 Coagulation Testing Hemostasis Unit 3 Chapter 17 Coagulation Testing Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

Coagulation Tests (cont.) Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

Automated ACT Analyzer Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

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 Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

von Willebrand Factor vWF required for platelet adhesion Performed when platelet function defects are evident Immunoassays in reference laboratories Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

Coagulation Factor Assays Performed in reference laboratories Occur due to and may alter clotting factors: Hereditary conditions Acquired conditions Copyright © 2015 by Mosby, an imprint of Elsevier Inc. All rights reserved.

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.