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Investigating
Abnormalities of
Calcium Metabolism
CALCIUM
The measurement of serum ionized calcium provides a
more precise estimate of an individual’s calcium status
than does total serum calcium, especially in the diseased
patient.8,26 Unfortunately, the majority of veterinary
pathology laboratories at the present time report only a
total calcium value measured by spectrophotometer,
reflecting the total combined levels of ionized calcium,
protein-bound calcium and complexed calcium. This can
lead to misinterpretation of calcium results in birds, as
any change in protein-bound calcium levels is not
thought to have any pathophysiological significance.22,26
Measurement of total calcium in an avian patient with
abnormal protein levels or acid-base abnormalities
would not truly reflect the calcium status of the animal.
Any state affecting serum albumin values in the blood
will affect the total calcium concentration, leading to an
imprecise result. In laying female birds, the serum albumin
levels may rise by up to 100%. This would produce
an inflated total calcium concentration due to an
increased protein-bound calcium fraction, while not
affecting the ionized calcium level. The binding reaction
between the calcium ion and albumin is strongly pHdependent,
so acid-base imbalances will affect ionized
calcium levels. Therefore, a patient with metabolic acidosis
would be expected to show an ionized hypercalcemia
level due to decreased protein binding. With an
alkalotic patient, an ionized hypocalcemia would occur
as the protein-binding reaction increases. Ionized calcium
levels are therefore considered a far more accurate
reflection of the patient’s calcium status, especially in a
diseased animal. In mammals, positive correlations have
been found between albumin and total calcium levels.8,26
This enables formulae to be developed that “correct”
total calcium levels for fluctuations in albumin levels.
Recent research has suggested these corrected estimates
of free calcium are inaccurate in 20 to 30% of cases in
mammals.8 In mammals, the relationship between total
calcium and albumin diminishes with the severity of the
disease, and the correction formulae are now thought to
be less useful. Previous research in psittacine birds
found a positive correlation between albumin and total
protein in African grey parrots, but not Amazons
(Amazona spp.);12,13 more recent research in healthy
African grey parrots has not indicated a significant relationship.
21,22 In the majority of cases, the measurement of
ionized calcium is preferred in both mammals and birds.
Ionized calcium levels are measured by ion-specific electrodes.
Analyzers using ion-selective electrodes are
increasingly available for use in veterinary clinics. The
methodology employed by the analyzers is based on the
ion-selective electrode (ISE) measurement principle to
precisely determine the ion values. The analyzers are
normally fitted with ISE electrodes to assay the electrolytes
sodium, potassium and ionized calcium. Each
electrode has an ion-selective membrane that undergoes
a specific reaction with the corresponding ions contained
within a particular sample. The membrane is an
ion exchanger reacting to the electrical charge of the
ion, causing change in the membrane potential or measuring
voltage, which is built up in the film between the
sample and the membrane. A galvanic measuring chain
within the electrode determines the difference between
the two potential values on either side of the membrane
of the active electrode. The potential is conducted to an
amplifier by a highly conductive inner electrode. The ion
concentration in the sample is then determined by using
a calibration curve produced by measuring the potentials
of standard solutions with a precisely known ion
concentration. Blood samples for ionized calcium assays
should be drawn into heparin and analyzed as soon as
possible after venipuncture, as changes in the blood pH
of the sample will affect the accuracy of the ionized calcium
levels (ie, contact with carbon dioxide in the air
will reduce the pH of the sample). Despite this, a study
in dogs suggests that samples will not be adversely
affected if not assayed for up to 72 hours, so it is possible
to use external laboratories.
This has been the author’s experience with avian samples, but it is advisable
to fill the sample tubes to minimize contact with
the air22 (Fig 5.1). It also is important to chill the samples
immediately to reduce glycolysis by the red blood cells,
which continue to produce lactic acid as a byproduct,
reducing the pH of the sample.
A recent study in healthy African grey parrots indicated a
narrow normal range for ionized calcium levels, but a
wide variation in total calcium levels due to protein fluctuated
among birds21,22 (Figs 5.2, 5.3). The study did not
reveal any significant correlation between albumin levels
and total calcium levels in healthy birds. It was shown
that using total calcium values in isolation would lead to
misdiagnosis of disorders of calcium metabolism in this
species. Of 394 samples submitted from African grey parrots
into the practice laboratory in 2001, 54 samples
(13.17%) had a low ionized calcium level despite having
normal total calcium concentrations, suggesting that
hypocalcemia is potentially under-diagnosed in this
species.22 In mature female birds, hypercalcemia might
be over-diagnosed due to increased protein-bound calcium
producing a high total calcium level, but ionized
levels would not be affected. Due to the potentially large
fluctuations in albumin levels in adult birds compared
with mammals, it is considered essential wherever possible
to measure ionized calcium levels.
So jetzt wirds bestimmt langweilig;O)
liebe Grüsse Luzy
Investigating
Abnormalities of
Calcium Metabolism
CALCIUM
The measurement of serum ionized calcium provides a
more precise estimate of an individual’s calcium status
than does total serum calcium, especially in the diseased
patient.8,26 Unfortunately, the majority of veterinary
pathology laboratories at the present time report only a
total calcium value measured by spectrophotometer,
reflecting the total combined levels of ionized calcium,
protein-bound calcium and complexed calcium. This can
lead to misinterpretation of calcium results in birds, as
any change in protein-bound calcium levels is not
thought to have any pathophysiological significance.22,26
Measurement of total calcium in an avian patient with
abnormal protein levels or acid-base abnormalities
would not truly reflect the calcium status of the animal.
Any state affecting serum albumin values in the blood
will affect the total calcium concentration, leading to an
imprecise result. In laying female birds, the serum albumin
levels may rise by up to 100%. This would produce
an inflated total calcium concentration due to an
increased protein-bound calcium fraction, while not
affecting the ionized calcium level. The binding reaction
between the calcium ion and albumin is strongly pHdependent,
so acid-base imbalances will affect ionized
calcium levels. Therefore, a patient with metabolic acidosis
would be expected to show an ionized hypercalcemia
level due to decreased protein binding. With an
alkalotic patient, an ionized hypocalcemia would occur
as the protein-binding reaction increases. Ionized calcium
levels are therefore considered a far more accurate
reflection of the patient’s calcium status, especially in a
diseased animal. In mammals, positive correlations have
been found between albumin and total calcium levels.8,26
This enables formulae to be developed that “correct”
total calcium levels for fluctuations in albumin levels.
Recent research has suggested these corrected estimates
of free calcium are inaccurate in 20 to 30% of cases in
mammals.8 In mammals, the relationship between total
calcium and albumin diminishes with the severity of the
disease, and the correction formulae are now thought to
be less useful. Previous research in psittacine birds
found a positive correlation between albumin and total
protein in African grey parrots, but not Amazons
(Amazona spp.);12,13 more recent research in healthy
African grey parrots has not indicated a significant relationship.
21,22 In the majority of cases, the measurement of
ionized calcium is preferred in both mammals and birds.
Ionized calcium levels are measured by ion-specific electrodes.
Analyzers using ion-selective electrodes are
increasingly available for use in veterinary clinics. The
methodology employed by the analyzers is based on the
ion-selective electrode (ISE) measurement principle to
precisely determine the ion values. The analyzers are
normally fitted with ISE electrodes to assay the electrolytes
sodium, potassium and ionized calcium. Each
electrode has an ion-selective membrane that undergoes
a specific reaction with the corresponding ions contained
within a particular sample. The membrane is an
ion exchanger reacting to the electrical charge of the
ion, causing change in the membrane potential or measuring
voltage, which is built up in the film between the
sample and the membrane. A galvanic measuring chain
within the electrode determines the difference between
the two potential values on either side of the membrane
of the active electrode. The potential is conducted to an
amplifier by a highly conductive inner electrode. The ion
concentration in the sample is then determined by using
a calibration curve produced by measuring the potentials
of standard solutions with a precisely known ion
concentration. Blood samples for ionized calcium assays
should be drawn into heparin and analyzed as soon as
possible after venipuncture, as changes in the blood pH
of the sample will affect the accuracy of the ionized calcium
levels (ie, contact with carbon dioxide in the air
will reduce the pH of the sample). Despite this, a study
in dogs suggests that samples will not be adversely
affected if not assayed for up to 72 hours, so it is possible
to use external laboratories.
This has been the author’s experience with avian samples, but it is advisable
to fill the sample tubes to minimize contact with
the air22 (Fig 5.1). It also is important to chill the samples
immediately to reduce glycolysis by the red blood cells,
which continue to produce lactic acid as a byproduct,
reducing the pH of the sample.
A recent study in healthy African grey parrots indicated a
narrow normal range for ionized calcium levels, but a
wide variation in total calcium levels due to protein fluctuated
among birds21,22 (Figs 5.2, 5.3). The study did not
reveal any significant correlation between albumin levels
and total calcium levels in healthy birds. It was shown
that using total calcium values in isolation would lead to
misdiagnosis of disorders of calcium metabolism in this
species. Of 394 samples submitted from African grey parrots
into the practice laboratory in 2001, 54 samples
(13.17%) had a low ionized calcium level despite having
normal total calcium concentrations, suggesting that
hypocalcemia is potentially under-diagnosed in this
species.22 In mature female birds, hypercalcemia might
be over-diagnosed due to increased protein-bound calcium
producing a high total calcium level, but ionized
levels would not be affected. Due to the potentially large
fluctuations in albumin levels in adult birds compared
with mammals, it is considered essential wherever possible
to measure ionized calcium levels.
So jetzt wirds bestimmt langweilig;O)
liebe Grüsse Luzy
rima:
also kaufen unsere TA das bestimmt in den nachsten hundert jahren..
