Background: The frequency of diagnosis of primary hyperparathyroidism increased dramatically with the advent of routine serum calcium measurements. The reliability of colorimetric serum calcium measurements is not well known.
Aim: To know the frequency of hyper and hypocalcemia in a population of healthy people and the reliability of serum calcium measurements.
Subjects and methods: Serum calcium was measured in 731 subjects participating in a preventive medical examination, using an automated colorimetric method. Serum albumin was also measured. In 31 randomly chosen serum samples, calcium was also measured by atomic absorption spectrometry. Normal serum calcium ranges were established as the mean +/- 1.34 SD of the sample.
Results: Mean serum calcium was 9 +/- 0.7 mg/dl, serum albumin was 4.3 +/- 0.5 g/dl and albumin corrected calcium levels were 8.7 +/- 0.7 mg/dl. Excluding lipemic sera, colorimetric calcium measurement had a correlation of 0.6 with atomic absorption spectrometry and a reliability of 17.9%. Using the proposed normal ranges (7.3-10.6 mg/dl), the frequency of hypercalcemia and hypocalcemia was 0.14 and 0.4% respectively.
Conclusions: Most subjects found to have hyper or hypocalcemia in this study were asymptomatic.