Page 497 - Problem-Based Feline Medicine

23 – THE BLEEDING CAT 489

tains platelet inhibitors and reduces platelet – The test is used most often for screening cats
clumping. It is commercially available in a with uremia prior to kidney biopsy.
vacuum tube (CTAD tube [formerly Diatube- – Do not routinely perform if cat has thrombocyto-
H], Becton Dickinson). penia. BMBT is usually prolonged when the
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– Manual agitation and vortex mixing of blood platelet count is < 50 × 10 /L (50 000/μl), and
samples does not reliably break up platelet progressive prolongation is expected with wors-
clumps. ening thrombocytopenia. A platelet count of
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– The effect of delay in processing the sample 10–15 × 10 /L (10 000–15 000/μl) is likely to
on the platelet count is controversial, but the result in a BMBT of 5–6 minutes. BMBT may be
general recommendation is to perform the performed in a cat with thrombocytopenia to
platelet count as soon after collection as pos- detect a concurrent platelet function defect, if
sible. bleeding is considered to be excessive for the
– Automated cell counters that use light- platelet count and clotting tests are normal.
scattering technology may detect platelet – Ketamine-acepromazine sedation is normally
clumps. used, but BMBT with other sedatives or anes-
– Some clumping may occur without dropping thetics is similar.
the platelet count below normal range. – Place cat in lateral recumbency and fold up the
– Examination of a blood smear is always rec- upper lip. Secure the lip with a tightly tied gauze
ommended. This can be used to verify a platelet strip passed through the mouth, around the head
count obtained by manual or automated methods. rostral to the ipsilateral ear, and caudal to the
This is especially important when platelet counts contralateral ear.
are obtained in-house using quantitative buffy – Avoiding obvious blood vessels, make a 5–6 mm
coat technology. long by 1 mm deep incision in the buccal mucosa
– Closely examine the feather edge of the blood of the everted lip above the molars or premolars;
smear to identify platelet clumps. Also examine this is best done using a spring-loaded device
the blood sample to identify a blood clot in the (e.g. Triplett Bleeding Time Device, Helena Labo-
tube. ratories). Blot the blood with a filter paper 1–2 mm
– Evaluation of a blood smear in a bleeding cat from the incision. The incision should not be
will rapidly determine whether or not the cat stretched or touched during the test. However, if a
is bleeding due to thrombocytopenia. fibrin film forms over the incision it should be
– If there are ≥ 1–2 platelets per oil field, it is teased away using the filter paper to touch the
unlikely the cat is suffering from sponta- blood as it wells up.
neous hemorrhage. If there are ≥ 3–4 – Normal BMBT is 1–3.25 min.
platelets per oil field, it is unlikely that the – Prolonged BMBT in an animal with a normal
cat will bleed excessively. platelet count indicates a vascular defect,
– If platelet clumps are present, the platelet platelet function defect or von Willebrand’s
count is probably adequate and bleeding is disease. Anemia will prolong bleeding time in
not due to thrombocytopenia. humans, rabbits, and dogs, but this effect has not
– The most reliable results are obtained with man- been evaluated in cats. A coagulopathy will not
ual counting, estimation from a well-prepared immediately affect BMBT, but rebleeding may
blood smear, and automated cell counters using occur. If the incision is made in an inflamed area,
flow cytometry. bleeding time will be prolonged.
– Reference ranges vary with the method of – In general, the longer the BMBT value, the more
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counting – a typical range is 200–600 × 10 /L likely the risk of bleeding, but there are no pre-
(200 000–600 000/μl). cise values defining the risk.
● Buccal mucosal bleeding time (BMBT). ● Activated clotting (coagulation) time (ACT).
– BMBT is typically used for detecting disorders – The intrinsic system is initiated by contact acti-
of platelet function when platelet numbers are vation. In the ACT siliceous (diatomaceous)
normal. earth or glass particles are used to provide a very