NOVA BIOMEDICAL Stat Profile PRIME, Instructions For Use Manual

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B-14
Prime CCS Instructions for Use Manual
Ionized Calcium “Normalized” to pH 7.4
The activity and concentration of ionized calcium in whole
blood is pH dependent. In vitro , a pH increase of 0.1 unit
decreases the ionized calcium level by 4 to 5% (conversely,
a pH decrease has an equal but opposite effect). The sample
of choice for ionized calcium determination is anaerobically
collected whole blood.
If an anaerobic sample is not available, by measuring
the actual pH of the sample at which the ionized calcium
concentration was measured normalized ionized calcium can
be calculated. The normalized ionized calcium represents
what the ionized calcium concentration would have been
if the initial pH was 7.40 (the midpoint of the pH reference
range). The equation used for this calculation is as follows:
log [iCa]
7.4
= log [Ca
++
]
X
- 0.24 (7.4 - X)
Equation 33
where X = measured pH of the sample
[iCa]
X
= ionized calcium concentration in the sample
at the measured pH
[iCa]
7.4
= normalized concentration of ionized calcium
at pH 7.40
The equation assumes a normal concentration of total protein
and may be used for measured values between pH 7.2 and
7.6. Between pH 6.9 and 7.2 and between pH 7.6 and 8.0,
modified forms of the equation are used. Normalized ionized
calcium values for samples with pH outside the range pH
6.9 to pH 8.0 are not displayed.