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

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Chapter | 28 Avian Clinical Biochemistry
Total calcium (mmol/l)
3.00
2.70
2.40
2.10
1.80
y 1.5 0.02x
FIGURE 28-18 Significant relationship (r 0.65;
p 0.01) between total protein and calcium in plasma
of 124 peregrine falcons ( Falco peregrinus ). The least
square regression line is indicated. As the concentration
of total protein decreases, there is a concurrent decrease
in plasma total calcium. About 42% of the variability in
calcium was attributable to the changes in the plasma
total protein concentration (R 2 0.417). Reprinted
with permission from Lumeij et al . (1993a) .
1.50
15 22 29 36 43 50
Total protein (g/l)
formula for tCa was: adjusted tCa (mmol/L) measured
tCa (mmol/L) 0.09 TP (g/L) 4.4.
Application of a correction formula in African grey
parrots, peregrine falcons, ostriches, and most likely other
species is indicated when extremely low or extremely high
plasma protein concentrations are found. The aforementioned
correction formulas are based on TP and Alb determinations
with the methods as outlined before (Section IV).
Application of a correction formula based on TP or Alb,
however, does not take into account the fraction of complexed
calcium, which can vary in different conditions. With the
development of ion selective electrodes, it is now possible to
measure iCa. It is to be expected that direct measurement of
iCa in avian blood will provide a more accurate assessment
of Ca status, compared to adjusted tCa, as was the case in a
canine study ( Schenk and Chew, 2005 ). One study ( Stanford,
2003a, 2003b ) yielded reference values for serum [sic] iCa
based on heparinized plasma samples from 80 “ healthy ”
seed-fed African grey parrots of 0.96 to 1.22 mmol/L
(3.84 to .88 mg/dl). Preliminary reference values for iCa in
blood of racing pigeons as established in our clinic (n 20;
inner limits of percentiles P 2.5 and P 97.5 with 90% certainty)
were 1.32 to 1.39 mmol/L when blood was sampled in electrolyte-balanced,
80 IU heparin, 2 ml syringes (Pico 50
Arterial Blood Sampler; Radiometer Medical A/S Denmark-
2700 Brønshøj – Ref 956–552) and 1.21 to 1.38 mmol/L
when sampled in 3 ml heparinized vacuum tubes (Venoject,
Terumo Europe N.V., 3001 Leuven, Belgium). Preliminary
data from our clinic from pellet-fed African grey parrots
established in blood samples collected with balanced Pico
syringes (Radiometer, Copenhagen) suggest that the reference
values for tCa values in this species are 2.6 to 3.4 mmol/
L and those for iCa are 1.35 to 1.68 mmol/L. Histological
changes in the parathyroid gland consistent with nutritional
secondary hyperparathyroidism were observed in individuals
with tCa values between 2.1 and 2.6 mmol/L (n 20; inner
limits of percentiles P 2.5 and P 97.5 with 90% certainty). These
reference values for iCa were significantly higher when compared
to values established by Stanford (2003a, 2003b). It is
most likely that the seed-fed parrots from Stanford (2003a,
2003b) were Ca-deficient, because Stanford (2003b) himself
showed that after 1 year of pelleted diet, iCa values
increased significantly in his experimental group of 20 parrots.
Furthermore, our findings in pigeon blood have shown
that the containers in which the blood is collected may affect
iCa values. The guidelines of the International Federation of
Clinical Chemistry specify that Ca can be bound by heparine
and that plasma binding sites in the anticoagulant should be
titrated in such a way that a maximum concentration of 15
IU/ml of heparine remains in the collecting tubes. In unbalanced
heparine tubes about 0.1 mmol/L of Ca will be bound
by 80 IU of heparine ( Boink et al ., 1991 ). For this reason,
tCa values as reported in Table 28.3 of this chapter, which
were determined in nonbalanced heparine tubes are likely
too low. Howard et al. (2004) established reference values
( “ 95% frequency intervals ” ) for iCa in thick-billed parrots
( Rhynchopsitta pachyrhyncha ) from 0.82 to 1.3 mmol/L and
for tCa from 1.37 to 2.06 mmol/L. These values were lower
than those reported for other psittacine species.
B . Hypercalcemia
1 . Introduction
Based on pathophysiological principles, the differential diagnosis
for hypercalcemia in birds includes hyperproteinemia,
estrogen-induced hypercalcemia, primary hyperparathyroidism,
pseudo-hyperparathyroidism, tertiary hyperparathyroidism,
metastatic, osteolytic skeletal tumors, and excess of
dietary calcium or vitamin D 3 (Lumeij, 1994c ), but actual clinical
cases, apart from protein-induced (pseudo)hypercalcemia
and vitamin D 3 toxicity, are poorly documented.
Clinical signs in true hypercalcemic states may include
hypercalcemia, anorexia, polyuria, and polydipsia (PU/PD),
delayed crop emptying, regurgitation, weight loss, depression,
and renomegaly ( Machlin, 1984 ). Gout has been associated
with hypervitaminosis D-induced hypercalcemia ( Brue,
1994 ; Ekstrom and Degernes, 1989 ; Flammer and Clubb,