Page 1379 - Small Animal Internal Medicine, 6th Edition

CHAPTER 82 Anemia 1351

thromboplastin time (aPTT), tests used routinely to monitor corticosteroid-induced diabetes mellitus. In my experience,
heparinization. The use of low-dose or minidose aspirin has azathioprine causes pronounced myelosuppression in cats
VetBooks.ir been associated with lower mortality rates in dogs with IHA. and should not be used.
One of the biggest dilemmas the clinician faces in the
Because dogs with IHA are at high risk for thromboembolic
events, I refrain from placing central venous lines; thrombo-
transfusion of blood or blood components. As a general rule,
sis of the anterior vena cava commonly leads to severe pleural treatment of a dog with IHA is whether to administer a
effusion in these dogs. Aggressive fluid therapy should be a transfusion should not be withheld if it represents a lifesav-
administered in conjunction with these treatments in an ing procedure. However, because patients with IHA are
attempt to flush the microaggregates of agglutinated RBCs already destroying their own antibody-coated RBCs, they
from the microcirculation. (Note: As a general rule, circulat- may also be prone to destroying transfused RBCs, although
ing blood does not clot.) In patients with severe anemia, the this has not been scientifically proven. My recommendation
resultant hemodilution may be detrimental. If deemed nec- is to administer a transfusion to any animal with IHA that
essary, oxygen therapy should also be used, but it is rarely is in dire need of RBCs (i.e., withholding a transfusion would
beneficial unless the HCT or Hb can be increased. result in the animal’s death). I usually pretreat these patients
As noted, I use human IV IgG (HIVIGG; 0.5-1 g/kg IV with dexamethasone sodium phosphate (0.5-1 mg/kg IV),
infusion, single dose) with a high degree of success in dogs administer fluids through an additional IV catheter, and con-
with refractory IHA. This treatment is aimed at blocking the tinue the heparin or aspirin therapy. Although cross-
Fc receptors in the MPS with a foreign Ig, thus minimizing matching is indicated, time is usually of the essence; therefore
the phagocytosis of antibody-coated RBCs. This treatment non–cross-matched “universal” donor blood or packed
appears to have other immunomodulatory effects as well. RBCs are frequently administered.
However, the product is moderately expensive (≈$700/dose Another issue pertaining to transfusion in dogs with
for a 10-kg dog). This approach has had such a positive IHA autoagglutination has to do with blood typing; if blood
impact, however, that I frequently use it as first-line therapy typing cards are used, the results will be false-positive for
in dogs with severe IHA. dog erythrocyte antigen (DEA) 1.1 (see later, “Transfusion
Drugs used for the maintenance treatment of dogs with Therapy”). Finally, no rule of thumb exists (e.g., PCV
IHA include prednisone (1-2 mg/kg PO q48h) and azathio- value, lack of response to oxygen therapy) regarding when
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prine (50 mg/m PO q24-48h), singly or in combination. to administer a transfusion. The clinician should use his
Azathioprine is associated with few adverse effects, although or her best clinical judgment to determine when a trans-
close hematologic and serum biochemical monitoring is fusion of blood or blood components is necessary (e.g.,
necessary because of its myelosuppressive and hepatotoxic does the patient exhibit tachypnea, dyspnea, or orthop-
potential; if myelosuppression or hepatotoxicity occurs, a nea?). If available, “universal donor” packed RBCs should
dose reduction is necessary. Occasionally azathioprine must be used instead of whole blood because they deliver a high
be discontinued in dogs with hepatotoxicity. oxygen-carrying capacity in a smaller volume; IHA is an
In cats, chlorambucil is an effective immunosuppressor isovolemic anemia.
with very low toxicity; I have used it successfully in cats with
IHA, immune-mediated thrombocytopenia, or other cyto- NONREGENERATIVE ANEMIAS
penias, 20 mg/m PO q2wk. As noted, in cats I use dexa- With the exception of ACD, nonregenerative anemias do not
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methasone (4-5 mg/cat PO q1wk) instead of prednisone or appear to be clinically as common as regenerative forms in
prednisolone. In general, dogs and cats with IHA require dogs, whereas the opposite is true in cats. Five forms of
prolonged, often lifelong, immunosuppressive treatment. nonregenerative anemia are typically recognized in cats and
Whether an animal requires continuous treatment is deter- dogs (see Box 82.3). Because IDA can be mildly to moder-
mined by trial and error; decremental doses of the immuno- ately regenerative, and the RBC indices are so different from
suppressive drug(s) are administered for a given period those in other forms of nonregenerative anemia (microcytic,
(usually 2-3 weeks), at which time the patient is reevaluated hypochromic versus normocytic, normochromic; see Boxes
clinically and hematologically. If the PCV has not decreased 82.3 and 82.4 and Tables 82.2 to 82.4) that it is easily identi-
or has increased, and the patient is clinically stable or has fied as such, I prefer to classify it in a separate category.
shown improvement, the dose is reduced by 25% to 50%. Anemia of endocrine disease is typically mild and usually is
This procedure is repeated until the drug is discontinued or an incidental finding in dogs with hypothyroidism or hypo-
the patient relapses. In the latter case, the dosage used previ- adrenocorticism (see Chapters 48 and 50). In general, most
ously that had beneficial effects is used again. In my experi- nonregenerative anemias and IDA in cats and dogs are
ence, most dogs with IHA require lifelong treatment. chronic, thus allowing for physiologic adaptation to the
Alternative treatments for dogs with refractory IHA include decrease in the RBC mass. As a consequence, these types of
cyclosporine, mycophenolate, mofetil, and possibly splenec- anemias may be detected incidentally during the routine
tomy. For details, see Chapters 72 and 73. evaluation of a cat or dog, which to the owner is asymp-
Chlorambucil (20 mg/m PO q2wk) appears to be the tomatic. In many cases (e.g., ACD), the anemia is mild, and
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best induction and maintenance agent in cats with IHA clinical signs are absent. Although most nonregenerative
refractory to corticosteroids or in those who develop anemias are chronic, two situations are commonly