Table 3. Laboratory Submission of Platelet-Surface-Associated Antibody Testing and Antimegakaryocyte Antibody Testing
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Demonstration of antiplatelet antibodies (Table 3) may support a diagnosis of immune-mediated thrombocytopenia but is not always necessary.8 Indirect assays (e.g. the platelet factor 3 test) detect platelet-bindable antibody in serum or plasma and have low sensitivity and specificity;
these assays are no longer available.13 Direct assays (e.g. flow cytometric assays, radioimmunoassays, or ELISAs) detect platelet-surface-associated antibodies and have higher sensitivity.2,5
Assays that measure total antibody are not reliable; assays that detect platelet surface-associated immunoglobulin should
be used.4 Alternatively, the antimegakaryocyte antibody test may be performed from slides of bone marrow aspirates.13 Treatment should not be withheld pending antiplatelet antibody test results. An additional limitation of antiplatelet antibody
testing is that it does not differentiate primary from secondary immune-mediated thrombocytopenia.2,5,8 Secondary causes of immune-mediated thrombocytopenia must be ruled out by appropriate diagnostic testing because response
to immunosuppressive therapy is the final step in confirming immune-mediated thrombocytopenia, but some patients with secondary
etiologies may respond positively initially.2,6
TREATMENT
Immune-mediated thrombocytopenia is a serious and potentially life-threatening disorder.8 Mortality rates of the initial episode of thrombocytopenia or relapse range from 25% to 30%.2,8 Death is mainly from acute gi hemorrhage or euthanasia.8 Aggressive initial therapy may improve survival rates. About 25% of dogs with immune-mediated thrombocytopenia require long-term
medication, and side effects are a principal reason for euthanasia in these patients.8 Recurrence after a variable period of clinical remission is common, occurring in about 40% of dogs.2,8
Initial supportive therapy
The initial management goals with immune-mediated thrombocytopenia are to stop bleeding, halt platelet destruction, and treat
any concurrent disease.6 A variety of supportive measures are indicated for a patient with severe thrombocytopenia. Ideally the patient should be
hospitalized and allowed to rest in a padded cage, with gentle handling to minimize trauma-related hemorrhage.2,18 Soft diets are fed to minimize gingival trauma.18,19 Avoid cystocentesis and intramuscular injections.18,19 Also avoid jugular venipuncture in patients with severe thrombocytopenia, and apply direct pressure to any venipuncture
or injection site for five minutes to ensure hemostasis. Intravenous catheters are not contraindicated, but if a jugular catheter
is required, placement should be done with great care, optimally after a transfusion with platelet-rich plasma.18
If the patient is hypovolemic, give crystalloids, colloids, or blood products as necessary.2 Hemodilution with synthetic colloids may decrease platelet function, so they should be used judiciously, and plasma should
be considered as an alternative.18 GI protectants may be administered to patients with signs of GI hemorrhage, although the benefit is not proven.19 Drugs that decrease platelet function (e.g. nonsteroidal anti-inflammatory drugs) should be discontinued or avoided.18 Doxycycline (5 to 10 mg/kg orally or intravenously every 12 hours) may be given to treat tick-borne disease, pending the
serum antibody titer results.20 If hyphema is present, administer topical 1% prednisolone acetate or 0.1% dexamethasone sodium phosphate three to four times
a day with topical 1% atropine two to four times a day.18
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