Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

VIII. Disorders of Iron Metabolism
273
Table 9-2 Iron Analytes in Various Stages of
Iron Deficiency
Analyte
Bone marrow
iron
Iron
Deficiency
in other iron-containing proteins including myoglobin,
cytochromes, citric acid cycle enzymes, and other heme
and nonheme iron-containing enzymes ( Kolb, 1963 ; Smith,
1997 ). Additional signs that may be present include diarrhea,
dermatitis, hematuria, hematochezia, and melena,
depending on the cause of the iron deficiency anemia and
the presence of other concomitant disorders. Iron-deficient
animals are more susceptible to infections because of lowered
immunity ( Kolb, 1963 ). Asymptomatic dogs are commonly
recognized serendipitously when complete blood
counts are done as a routine screen before surgery and
microcytic anemia is found.
2 . Causes of Iron Defi ciency
Iron-Deficient
Erythropoiesis
Low Low Low
Serum ferritin Low Low Low
Serum iron Normal Low Low
Zinc
protoporphyrin
Transferrin
saturation
Blood
hemoglobin
Erythrocyte
size
From Hastka et al . (1994) .
Normal High High
Normal Low Low
Normal Normal Low
Normal Normal Low
Iron
Deficiency
Anemia
With the exception of young growing animals, iron deficiency
in domestic animals usually results from blood
loss. Chronic iron deficiency anemia is common in adult
dogs and ruminants in areas where bloodsucking parasite
infestations are severe ( Harvey et al ., 1982 ; Weiser and
O’Grady, 1983 ). Chronic hemorrhage resulting in iron
deficiency may also occur with intestinal neoplasms, transitional
cell carcinomas, gastrointestinal ulcers, thrombocytopenia,
inherited hemostatic disorders, hemorrhagic
colitis, and menorrhea (primates only). Excessive removal
of blood from a blood donor animal can result in an irondeficient
state. Iron deficiency anemia appears to be rare
in adult cats and horses ( French et al ., 1987 ; Fulton et al .,
1988 ; Smith et al ., 1986a ).
Milk contains relatively low concentrations of iron
( Anderson, 1992 ; Kolb, 1963 ); consequently, nursing
animals can easily deplete body iron stores as they grow
( Kolb, 1963 ; Smith, 1997 ). Piglets reared in modern facilities
without access to soil are especially susceptible to the
development of dietary iron deficiency anemia because
they have lower iron stores at birth than other domestic
animals studied, and they exhibit remarkably rapid growth
while nursing ( Kolb, 1963 ; Underwood, 1977 ). Iron deficiency
can be prevented in piglets by allowing them to eat
earth while rooting in open fields or by adding pieces of
sod to their pens; however, iron deficiency is generally prevented
by intramuscular iron dextran injections when pigs
are raised in confinement ( Kolb, 1963 ; Underwood, 1977 ).
The concomitant occurrence of bloodsucking parasite
infestations can result in especially severe iron deficiency
anemia in nursing animals. Once the consumption of solid
food begins, dietary iron deficiency in growing animals
usually resolves ( Kolb, 1963 ). At least 80mg available iron
per kilogram diet is required to avoid iron-limited erythropoiesis
in puppies, kittens, and piglets ( Chausow and
Czarnecki-Maulden, 1987 ; Kolb, 1963 ). Iron deficiency
anemia is an unavoidable consequence of feeding practices
designed to produce pale meat in veal calves ( Miltenburg
et al ., 1992a ).
3 . Laboratory Findings
Anemia in iron-deficient animals generally results from a
combination of hemorrhage and impaired (iron-limited)
erythrocyte production. However, iron-deficient erythrocytes
also exhibit decreased life spans, with evidence of
enhanced eryptosis characterized by cell shrinkage, membrane
blebbing, and surface exposure of phosphatidylserine
(Kempe et al ., 2006 ). The hematocrit decreases before the
MCV and MCHC decrease, especially when iron deficiency
is caused by bleeding. The MCV is generally normal in
acute iron deficiency. If the iron-deficient state persists for
weeks to months, the number of microcytic cells produced
can constitute a sufficient enough portion of the erythrocyte
population to reduce the MCV below the normal reference
intervals. Iron deficiency anemia is defined as iron
deficiency that results in microcytic anemia. Because erythrocyte
indices are generally normal during early iron deficiency,
most cases of iron deficiency go undiagnosed at this
stage. Microcytic erythrocytes are produced in response to
iron deficiency in nursing kittens and pups, but low MCV
values may not develop postnatally because the MCV is
above adult values at birth in these species and some fetal
macrocytes may persist during the iron-deficient nursing
period. The review of erythrocyte volume histograms can
reveal the presence of microcytes in iron-deficient pups and
kittens that have normal MCV values ( Weiser and Kociba,
1983 ). New hematology instruments have the ability to calculate
the percentage of microcytes present.
The mean cell hemoglobin concentration (MCHC)
within iron-deficient erythrocytes may be low because iron