Page 1382 - Small Animal Internal Medicine, 6th Edition

1354 PART XIII Hematology

transfusions of blood or packed RBCs are sometimes neces- PCV ≥10%; the median time to hematologic response was
sary. Because these patients are normovolemic, the latter is 29 days. No dog sustained a response at a dosing interval
VetBooks.ir preferable. In addition, because transfusions may need to be >q21 days. Potential adverse events included increased blood
pressure requiring treatment (n = 12), seizures (n = 5), vom-
administered on an ongoing basis, cross-matching is recom-
mended before the administration of each transfusion. Of
(Fiocchi et al., 2017).
note, in dogs one of the mechanisms of adaptation to chronic iting (n = 3), diarrhea (n = 3), and possible PRCA (n = 2)
hypoxia (e.g., anemia) is an increase in the intraerythrocytic
2,3-diphosphoglycerate (2,3-DPG) concentration, resulting Acute and Peracute Blood Loss
in a lower oxygen affinity; that is, the delivery of oxygen to or Hemolysis
the tissues is facilitated. Because stored RBCs have lower After an acute episode of blood loss or hemolysis, the bone
concentrations of 2,3-DPG, the transfused cells have a higher marrow takes approximately 48 to 96 hours to release enough
affinity for oxygen. As a result, the transfusion of stored reticulocytes to result in regeneration. Therefore blood loss
blood to a patient with chronic anemia may result in tran- and hemolytic anemias are nonregenerative during the initial
sient decompensation because approximately 24 hours is phases of recovery.
usually required for the transfused, stored RBCs to regain In most dogs and cats with acute blood loss, profound
50% of the normal 2,3-DPG concentration and become bleeding is historically or clinically evident. If no obvious
recharged. cause of bleeding is found, or if the patient is bleeding from
Myelophthisis, myelodysplastic syndromes, multiple sites, the hemostatic system should be evaluated in
myelofibrosis, and osteosclerosis-osteopetrosis search of a coagulopathy (see Chapter 87). Sites of internal
These disorders are discussed in Chapter 86. bleeding should be evident after a complete physical exami-
nation is performed.
Anemia of Renal Disease Once the bleeding has been stopped, the anemia typically
The kidney is the main site of production of EPO, the prin- resolves within days to weeks. The initial management of
cipal stimulus of erythropoiesis. In addition, in dogs and cats a bleeding episode should include supportive therapy and
with CKD, the life span of RBCs is considerably shorter and IV crystalloids or plasma expanders. If necessary, blood
subclinical to clinical GI tract bleeding is present; high con- or packed RBCs or Hb solutions, if available, should be
centrations of parathyroid hormone may also suppress administered.
erythropoiesis. Consequently, anemia is common in these The management of dogs with peracute hemolysis was
patients. The anemia is usually normocytic and normochro- discussed earlier in the chapter.
mic, with few or no reticulocytes. HCT levels in dogs and
cats with ARD are usually in the 20% to low 30% range, Iron Deficiency Anemia
although HCT levels from 13% to 19% are common. Of note, IDA is traditionally classified as nonregenerative, even
the HCT in these patients is usually that low only after they though mild to moderate regeneration usually occurs. More-
have undergone intensive fluid therapy; on presentation, the over, as noted, the RBC indices in dogs and cats with IDA
anemia is not that severe because the patients are markedly are microcytic and hypochromic, distinguishing it from
dehydrated. other forms of anemia. When evaluating the CBC of a dog
Improvement in renal function may result in marginal with microcytic hypochromic anemia, the clinician must
increases in the RBC mass. Anabolic steroids are rarely ben- remember that microcytosis occurs in some breeds (e.g.,
eficial in improving the anemia in these patients. Human Akita, Shiba Inu, Shar Pei) and in dogs with other disorders,
recombinant EPO has been used successfully to treat anemia such as portosystemic shunts (see Table 82.2).
in cats and dogs with chronic renal failure. A dose of 100 to This form of anemia is well characterized in dogs with
150 IU/kg SC, twice weekly, is administered until the HCT chronic blood loss. In cats, IDA has been well documented
returns to a target value (usually 20%-25%); the interval only in weanling kittens in whom iron supplementation
between injections is then lengthened for maintenance results in rapid resolution of the clinical and hematologic
therapy. The HCT usually returns to normal within 3 to 4 abnormalities. IDA is extremely uncommon in adult cats; I
weeks of the initiation of treatment. Given the fact that this have seen it primarily in association with chronic blood loss
EPO is foreign to dogs and cats, an appropriate antibody in cats with GI lymphoma. Given its rarity in cats, the fol-
response usually nullifies the beneficial effects of long-term lowing discussion of IDA pertains primarily to dogs.
therapy (6-8 weeks) in more than 50% of patients. Recently, Chronic blood loss leading to iron depletion is common
darbepoetin was successfully used to treat anemia of renal in dogs with GI tract bleeding caused by neoplasia, gastric
disease in dogs (Fiocchi et al., 2017). In a study of 33 dogs ulcers, or endoparasites (e.g., hookworms), and in those with
with CKD and anemia, the median starting dosage and a heavy flea infestation. Other causes of chronic blood loss,
highest dosage of darbepoetin administered were 0.5 and such as urogenital bleeding and iatrogenic bloodletting, are
0.8 µg/kg SC once weekly, respectively. Response to treat- extremely rare. Recently, in a multicenter study of 688 dogs
ment was defined as achieving a PCV ≥30% or an increase and 163 cats, the prevalence of anemia upon admission was
in PCV ≥10%. Twenty-eight of 33 dogs (85%) achieved a 32%; the overall prevalence during the hospitalization period
PCV ≥30%, and 22 of 33 (67%) dogs achieved an increase in was 56% (Lynch et al., 2015). The RBC indices were not