Assessment of bleeding disorders

Spontaneous bleeding following surgery or trauma is relatively common in dogs but rare in cats. Differentials include thrombocytopenia, coagulopathies (congenital and acquired), platelet function abnormalities, Von Willebrand's disease and disseminated intravascular coagulation (DIC). Distinguishing between these differentials requires a combination of the following procedures and tests:

History:

• Previous spontaneous bleeds?
• Excessive haemorrhage at previous surgery?
• Rodenticide access?
• Current drug therapy?
• Recent vaccination with a modified live vaccine?

Clinical Examination:

• Site(s) of bleeding—see below.
• Evidence of:
  • localised cause of the bleeding (inflammatory, neoplastic, necrotic)
  • neoplastic disease (solitary, disseminated)
  • splenic disease (splenomegaly, torsion)
  • toxaemia (endotoxaemia, uraemia)
  • haemolytic disease (immune-mediated, microangiopathy)
  • liver disease (necrosis, severe obstructive disease)
  
  
  

Table 1a. Clinical Presentations of Platelet and Coagulation Factor Abnormalities

1. Patient-Side Testing

Clinical testing is generally not required since patients present with evidence of excessive or prolonged haemorrhage.

1.1 Bleeding Time (Buccal Mucosal Bleeding Time)

This is a test of vascular response, platelet number and function, low platelet numbers and/or impaired platelet function (Von Willebrand's disease, NSAID therapy, severe uraemia may all significantly prolong bleeding time). Bleeding time in coagulopathies is normal, but there may be subsequent re-bleeding from the site.

Materials:

• Simplate-II: This device produces two parallel incisions of standard length and depth. It is supplied in a sterile pack and can be triggered once only. These are available from the laboratory upon request.
• Stop watch
• Filter paper
• Gauze bandage (5 cm width)

Method:

• Position the patient in lateral recumbency. Sedation with ketamine, atropine and acepromazine is recommended in cats. While many dogs will tolerate this procedure conscious, sedation with Xylazine or anaesthesia with Halothane may be required for fractious individuals. Place the strip of gauze around the maxilla to fold up the upper lip, causing moderate engorgement of the mucosal surface (see Figure 1).
• Remove Simplate from the blister pack and twist off the white safety fob: Do not push the trigger or touch the blade slot.
• Position the device vertically on the buccal mucosa, avoiding any obvious superficial vessels. Hold firmly but avoid excessive pressure.
• Depress the trigger and simultaneously start the timer. Remove the Simplate approximately 1 second after triggering.
• At 15 seconds, blot the flow of blood with filter paper placed 1-3 mm below the incision without dislodging the clot.
• Blot in a similar manner every 15 seconds until blood no longer stains the filter paper. Stop timer.
• Both incisions usually cease bleeding almost simultaneously (if this does not occur, the last incision to cease bleeding has lacerated a vessel).

Figure 1:

Table 1b. Normal Times

1.2 Coagulation Time (Whole Blood Clotting Time)

This test is unreliable when using tube methods, but absence of clotting in a glass tube after 15 minutes is suggestive of a deficiency of clotting factors.

1.3 Clot Retraction

This tests the ability of the platelets to contract the formed clot. Poor retraction reflects low platelet numbers or impaired function. This test is not sensitive.

1.4 Platelet Estimation

Examination of the monolayer of a Giemsa or "Diff-Quick" stained blood smear under oil allows an estimation of platelet numbers. Each platelet per field is approximately equal to 12-15 x 10⁹/l. The sample should be examined for clots and the tail edge of the smear should be examined for platelet clumps which would falsely lower the count.

2. Laboratory Testing

All samples should be taken before therapy (including transfusion and vitamin K therapy). It is essential to submit the correct tubes, filled to the line with blood collected at a first attempt. Tubes must be in date and posted to minimise a delay in transit. Any suspicion of a clot is an indication for re-sampling. The PT and PTT reflect the extrinsic and intrinsic coagulation pathways. Fibrinogen and FDPs are important considerations in the diagnosis of disseminated intravascular coagulation.

Table 2. Specimens Required

The IDEXX Profile "COAG" includes a platelet count, PT, PTT, Fibrinogen and FDPs.

Please enter this in the Practice Profile box on the request form.

NB: Where not previously performed, COAG should be combined with a Full Blood Count and Biochemistry profile.

2.2 Interpretation

Combining the findings of the history, clinical examination, patient-side screening tests and laboratory evaluation should allow the nature of the problem to be defined. Veterinary interpretation is provided with the "COAG" profile where the appropriate clinical information is supplied.

References:

Veterinary Clinical Pathology, 7:9 1988, Oral mucosa bleeding times of normal cats and cats with Chédiak-Higashi Syndrome or Hageman Trait (factor XII deficiency), Parker, M.T., Collier, L.L., Kier, A.B., et al.

American Journal Veterinary Research, 48:1337 1987, Buccal mucosa bleeding times of healthy dogs and of dogs in various pathologic states, including thrombocytopenia, uraemia, and von Willebrand's disease, Jergens, A.E., Turrentine, M.A., Kraus, K.H., et al.