Microdetermination of Serum Calcium by Parallel Fast Analyzer

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Abstract
An adaptation of a direct microdetermination of serum calcium based upon its colored reaction product with cresolphthalein complexone for use with a parallel fast analyzer is described. It is simple, reliable and clinically accurate. Twenty microliters of sample are employed in a final volume of 650 μl. Comparison studies with an atomic absorption method resulted in a correlation coefficient (r) of 0.94. Replicate analyses at normal (8.5 mg. per dl.) and abnormal (12.1 mg. per dl.) levels showed inter-day coefficients of variation of 3.2 and 2.3%, respectively. Assays of sera of male and female donors (age range: 17–60 years) showed normal ranges of 8.5–10.8 and 8.5–10.5 mg. per dl., respectively. Moderate hemolysis and jaundice and mild lipemia are associated with spuriously high results. Magnesium in serum showed no significant effect below 4.0 mEq. per 1.