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

270
Chapter | 9 Iron Metabolism and Its Disorders
SATURATION
(%)
TIBC
(µg/dl)
IRON
(µg/dl)
80
60
40
20
600
500
400
300
350
250
150
50
0 1 2 3 4 5 6 7 8 9
DAYS
FIGURE 9-7 Effect of oral prednisone (2 mg/kg bid) administration
for 3 consecutive days (arrows) on serum iron parameters in dogs
(closed circles with solid lines) compared to control dogs without prednisone
(open circles with dashed lines). Values are mean standard error
with stars indicating significant differences between groups ( p 0.05).
TIBC total iron-binding capacity. Saturation refers to the percentage
saturation of transferrin with iron. From Harvey et al . (1987b) , with
permission.
decreases to adult values by 3 days of age ( Harvey et al .,
1987a ). Although serum iron values in calves and piglets
are not as high as values in foals at birth, a rapid decrease
in serum iron also occurs in these species within a few days
after birth ( Kolb, 1963 ). Serum iron increases markedly in
chickens associated with increased estrogen secretion and
the onset of egg laying ( Kolb, 1963 ). Serum iron values
may be spuriously increased if laboratory tubes or pipettes
used to handle serum are contaminated with iron. The use
of disposable plastic pipettes and tubes minimizes this possibility.
Iron concentrations may be spuriously increased in
plasma samples if kits designed for serum iron determinations
are used to measure iron in plasma.
Serum iron concentration is generally low in both iron
deficiency ( Furugouri, 1972 ; Halvorsen and Halvorsen,
1973 ; Harvey et al ., 1982 ; Harvey et al ., 1987a ; Kolb,
1963 ; Mollerberg et al ., 1975 ; Weiser and Kociba, 1983 )
and with inflammation ( Borges et al ., 2007 ; Feldman et al .,
1981b ; Kolb, 1963 ; Neumann, 2003 ; Smith and Cipriano,
1987 ; van Miert et al ., 1986 ; van Miert et al ., 1990 ). It may
also be decreased when demands for erythropoiesis exceed
the iron flow from the diet and storage pools, such as
might occur with erythropoietin administration ( Brugnara
et al ., 1993 ; Cowgill et al ., 1998 ; Pak et al ., 2006 ). Serum
iron concentration is decreased following glucocorticoid
administration to cattle and goats ( Maddux et al ., 1988 ;
van Miert et al ., 1986 ; Weeks et al ., 1989a ).
TIBC (µG/dl)
SERUM FERRITIN (ng/ml)
IRON SATURATION (%)
700
600
500
400
250
200
150
100
50
0
90
80
70
60
50
40
30
20
10
0
0 5 10 15 20 25 1 2 3 4 5 6 7 8 9 101112
DAYS
MONTHS
FIGURE 9-8 Serum total iron-binding capacity (TIBC), ferritin concentration,
and percentage saturation of transferrin with iron (mean standard
error) from 21 healthy foals during the first year of life. The day 0 sample
was taken before foals were allowed to nurse. The sharp increase in serum
ferritin when 1 day old resulted from the consumption of colostrum with
high ferritin concentration compared to that in blood. Values marked with
a star were significantly different from 77 healthy adult horses. From
Harvey et al . (1987a) , with permission.
C. Serum Total Iron-Binding Capacity
The total iron-binding capacity (TIBC) of serum is a
measure of total serum transferrin (apotransferrin, monotransferrin,
diferric transferrin) concentration because
insignificant amounts of plasma iron are bound to other
proteins. TIBC is calculated by measuring serum iron and
serum unsaturated iron-binding capacity and summing
these values. The percentage saturation of transferrin with
iron is calculated by dividing the serum iron concentration
by the TIBC and multiplying by 100. Serum TIBC is
low-normal or decreased in association with inflammatory
disorders ( Feldman et al ., 1981b ; Ottenjann et al ., 2006 ;
Smith and Cipriano, 1987 ) and increased in iron-deficient
humans, rabbits, pigs, horses, and cattle ( Furugouri, 1972 ;
Halvorsen and Halvorsen, 1973 ; Harvey et al ., 1987a ;
Miltenburg et al ., 1992b ; Mollerberg et al ., 1975 ). A slight
increase in serum TIBC was reported in an experimental
study of diet-induced iron deficiency anemia in young