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Evaluating the Bleeding Patient: Point-Of-Care Tests

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Evaluating the Bleeding Patient: Point-Of-Care Tests procedures pro HEMOSTASIS Evaluating the Bleeding Patient: Point-of-Care Tests Marjory Brooks,DVM,Diplomate ACVIM,Comparative Coagulation Section,Animal Health Diagnostic Laboratory,Ithaca,New York EMORRHAGE is a common chief complaint that prompts veterinary attention. Although the cause Hof hemorrhage is often apparent from physical examination alone, some cases require diagnostic testing to help differentiate blood loss due to a breach in blood vessel integrity from a systemic failure of normal hemostatic processes. Bleeding diatheses are broadly classified as defects of platelet plug formation (primary hemostasis) or fibrin clot formation (secondary hemostasis). While there is no single “global” test for hemostasis, simple point-of-care tests can be done to detect the primary and secondary hemostatic defects often encountered in clinical practice. Estimation of platelet count from a stained blood smear readily identifies thrombocytopenia, the most com- mon canine and feline hemostatic abnormality. The ACT is a screening test of the intrinsic and common coagulation pathways, and a prolonged ACT is found in most patients with clinically significant coagulation factor deficiencies. The BMBT is an in vivo test of primary hemostasis that can aid in identifying patients with severe platelet dysfunction and severe von Willebrand’s disease. The following discus- sion describes the procedures for performing these screen- ing tests. Point-of-Care Tests for Hemostasis • Platelet Estimate from Blood Smear • Activated Clotting Time • Buccal Mucosa Bleeding Time continues ACT = activated clotting time; BMBT = buccal mucosa bleeding time; CBC = complete blood count; DIC = disseminated intravascular coagulation; EDTA = ethylenediaminetetraacetate; OIF = oil immersion field procedures pro......................................................................................................................NAVC clinician’s brief...november.2006.....83 procedures pro C ONTINUED STEP BY STEP HOW TO TEST FOR HEMOSTASIS PLATELET ESTIMATE FROM Test Interpretation & Additional BLOOD SMEAR PROCEDURE PEARL Diagnostic Evaluation Carefully examine the feathered edge Although mild thrombocytopenia develops in of the smear to detect platelet clump- What You Will Need many disease syndromes, clinical signs of ing, the most common cause of spuri- • Whole blood collected in antico- ous low platelet counts and inaccurate abnormal hemostasis are typically seen in agulant. EDTA blood samples platelet estimate. patients with platelet counts below 50,000/µl. drawn for CBC are typically used. The finding of low platelet numbers from the • Clean glass slides initial slide estimate should be followed with • Cytology stain (eg, Wright’s stain, a CBC, including platelet count, and additional Examine the feathered end of the Diff-Quik) tests to differentiate platelet production smear at low magnification to 3 defects, sequestration or consumption defects, detect platelet clumping that would or immune-mediated platelet destruction. result in an inaccurate estimation of the Avoid platelet activation during These tests can include bone marrow exami- platelet count. 1 blood collection and processing by nation, splenic aspiration cytology, serologic careful venipuncture: draw blood evaluation to detect infectious agents, coagu- Examine the smear under oil immer- directly into a tube or lation testing to define a DIC process, and sion (1000 ), scanning fields with syringe containing anti- 4 × measurement of platelet-bound antibody. red cells distributed in a single layer. coagulant, gently mix the sample, maintain Determine the average number of the sample at room platelets in 10 OIFs. temperature, and pre- 5 pare the smear as soon Estimate platelet count using the as possible after blood following formula: PROCEDURE PEARL collection. 6 The finding of at least 10 to 12 average # platelets/OIF × 15,000 = platelets/µl platelets per OIF indicates a normal Prepare and platelet count. 2 stain the blood smear. Stained smear NORMAL FELINE BLOOD SMEAR Arrowheads indicate platelets. Note the range in platelet size (100 objective). × NORMAL CANINE BLOOD SMEAR Arrowheads indicate platelets (100 objective) EDTA blood sample and unstained smear × 84...november.2006.....NAVC clinician’s brief ......................................................................................................................procedures pro ACTIVATED CLOTTING TIME Warm the ACT tube to 37º C for Test Interpretation & Additional One-Tube Technique* 1 1 minute before sampling. Diagnostic Evaluation ACT is prolonged in the following conditions: Perform venipuncture and collect What You Will Need deficiency of one or more coagulation factors blood directly into the ACT tube. • 21- or 22-gauge needle 2 in the intrinsic and common pathways, fibrino- • ACT sample tube (evacuated tube gen deficiency, and heparin anticoagulant Allow the tube to completely fill by containing a particulate activator) effect. Specific coagulopathies that prolong vacuum. • 37º C heating block or water bath 3 ACT include anticoagulant rodenticide toxicity, • Timer or stopwatch severe liver disease, hemorrhagic DIC, and Immediately after the blood is such hereditary factor deficiencies as hemo- 4 drawn, gently tilt the tube several philia A (Factor VIII deficiency), hemophilia B times to mix the blood with the (Factor IX deficiency), and Factor XII deficien- activator and start the timer. cy. The finding of prolonged ACT should be fol- lowed with a full coagulation panel (activated Place the tube in a 37º C heating partial thromboplastin time, prothrombin time, 5 block or water bath. fibrinogen assay) and specific factor analyses if needed for a definitive diagnosis. After a 45-second incubation time, 6 gently tilt the tube at 10-second continues intervals to detect clot formation. The ACT is the time elapsed from PROCEDURE PEARL PROCEDURE PEARL blood collection to clot formation. Blood collection from peripheral veins 7 An ACT reference range should be is preferable, if patient size allows, to established in-house for the manual or minimize risk for hematoma formation Expected ACT for dogs is instrument method in use. at the jugular vein. 8 less than 120 seconds; for cats less than 165 seconds. Close-up of ACT tube containing the particulate mat- Close-up of blood in the ACT tube immediately after Close-up of formation of a fibrin clot in the ACT ter that acts as a contact activator of coagulation collection. Note that the blood is freely flowing and tube. The clot protrudes into the tube lumen when therefore evenly dispersed in the tilted tube. the tube is tilted. * A two-tube technique is also common. A study in cats revealed no difference between the one- and two- PROCEDURE PEARL PROCEDURE PEARL tube techniques in terms of outcomes. The method The ACT can be measured using auto- The ACT is influenced by nonspecific described here and the expected values are those used mated instruments that warm the sam- variables (such as platelet count, incu- in the author’s laboratory. Canine methods papers have ple and then detect and display the described test initiation both at the beginning and end bation temperature, blood viscosity, of blood draw.1-3 time for clot formation in a reaction hematocrit) in addition to prolonga- cuvette. tion caused by coagulation factor defi- ciencies and anticoagulant therapy. ACT = activated clotting time; DIC = disseminated intravascular coagulation continues procedures pro ......................................................................................................................NAVC clinician’s brief...november.2006.....85 procedures pro C ONTINUED Simultaneously trigger the device to BUCCAL MUCOSA BLEEDING TIME PROCEDURE PEARL incise the mucosa and start a timer. 4 The BMBT is prolonged in patients What You Will Need with severe platelet dysfunction and severe von Willebrand’s disease; how- • Muzzle gauze Blood flows freely from the BMBT ever, other variables, such as hemat- • Stopwatch or timer 5 wounds immediately after incision. ocrit, platelet count, and operator • Bleeding time template device Gently blot underneath the incision technique, can influence the test. (Surgicutt—ITC, Edison, NJ; with filter paper or gauze to collect blood Simplate—Organon Teknika, flowing from the wound. Do not wipe or Durham, NC) directly touch the wound. Test Interpretation & Additional • Filter paper or gauze sponge Diagnostic Tests The BMBT is the time from trigger- 6 ing the device until cessation of Mild to moderate platelet dysfunction occurs blood flow. in many common diseases and secondary to drug therapy; therefore, initial follow-up After completion of the test, remove should include complete history and general 7 the gauze and apply direct pressure medical evaluation. Marked prolongation of to the wounds. If needed, tissue BMBT (> 12 minutes) in patients with normal glue can be applied to prevent rebleeding. platelet count is compatible with a lack of von Willebrand’s factor or failure of platelet aggre- The expected BMBT for dogs is less gation. Definitive diagnosis of these condi- Position the patient in sternal or 8 than 4 minutes. tions is based on specific measurement of lateral recumbency. plasma von Willebrand’s factor concentration 1 or platelet aggregation testing. I Evert the upper lip and use a PROCEDURE PEARL strip of gauze wrapped snugly Although the incision causes only PROCEDURE PEARL 2 around the muzzle to secure the momentary discomfort, it is easier to The BMBT has proven to
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