Page 1262 - Small Animal Internal Medicine, 6th Edition

1234 PART XI Immune-Mediated Disorders

TABLE 73.1
VetBooks.ir Expected Changes on the CBC in Different Causes of Anemia EVIDENCE OF

RATE OF
DECREASE OF RETICULOCYTE SERUM INFLAMMATION
TYPES HEMATOCRIT COUNT PROTEINS ON CBC THROMBOCYTOPENIA
Hemolytic anemia Fast High No change Yes Yes (mild to severe)
Nonregenerative anemia Slow Low No change No Depends on cause
Blood loss anemia Fast High Decreased No Yes (mild only)

CBC, Complete blood cell count.

TABLE 73.2
Semiquantitative Scoring System for Numbers of
Spherocytes on a Slide
APPROXIMATE NUMBER OF
SPHEROCYTES PER × 1000 FIELD ASSIGNED SCORE
1-10 1+
11-50 2+
A
51-150 3+

of canine patients with IMHA have a positive Coombs test.
Conversely, a positive Coombs test can occur in a variety of
other inflammatory diseases causing false-positive results.
False-negative results can also occur and might reflect a
low concentration of antibody present (see Chapters 72
and 82). In people, the Coombs test is performed at two
different temperatures, to detetct cold and warm aggluti-
nins, maximizing the possibility of identifying a positive
result. There is some evidence in people that cold agglu-
tinin positive/warm agglutinin negative Coombs tests are
more likely to indicate IMHA due to a secondary cause. This
has not been shown to be true in dogs, but certain labora-
tories will still report cold and warm agglutinin Coombs
test results.
A search for secondary causes of IMHA should always be
undertaken in a dog or cat with IMHA because the underly-
ing disease may influence both management strategy and
prognosis. Potential secondary causes of IMHA are listed in
B Table 73.3. The diagnostic approach to ruling out secondary
IMHA includes a thorough history of drug, vaccine, and
FIG 73.3 toxin exposure; detailed physical examination, including
Blood smear showing gross (A) and microscopic (B) rectal, ophthalmologic, and neurologic examinations; tests
agglutination. Note the three-dimensional clustering of red
blood cells on the microscopic view. for specific infectious diseases; investigation into causes of
chronic antigenic stimulation; and a search for evidence of
neoplasia. Diagnostic tests to consider in addition to a CBC,
confirming a diagnosis of IMHA. A positive Coombs test biochemical panel, and urinalysis include urine culture,
indicates that antibody, complement, or both are on the abdominal and thoracic radiographs, abdominal ultrasound,
surface of the RBC but does not mean that the antibody is bone marrow cytology and/or histopathology (if the anemia
directed specifically against the RBC membrane or that the is nonregenerative), and appropriate titers for infectious
antibody is causing hemolysis. Approximately 60% to 80% diseases.