Discrepancy between serum 1,25-dihydroxycholecalciferol measured by radioimmunoassay and cytosol radioreceptor assay

Abstract

Hummer L, Christiansen C, Tjellesen L. Discrepancy between serum 1,25-di-hydroxycholecaliferol measured by radioimmunoassay and cytosol radio-receptor assay. Scand J Clin Lab Invest 1985; 45: 725–733.

A radioimmunoassay for determination of 1,25-dihydroxycholecalciferol (1,25(OH)₂ D₃) in serum, was compared with the radioreceptor assay using cytosol receptor from rachitic chick intestine in order to clarify whether differences in specificity can explain discrepancies in the clinical application of the two techniques. In the literature, seasonal fluctuations in serum 1,25(OH)₂D₃ are only observed when using radioimmunoassay. Treatment of anticonvulsant osteomalacia with vitamin D₃ results in a marked increase in radioimmunologically measured 1,25(OH)₂D₃, but no effect on the serum 1,25(OH)₂ D level, measured by the radioreceptor assay, could be observed. The present study demonstrates that another unknown compound is coeluted on high pressure liquid chromatography with 1,25(OH)₂ D₃, and recognised only by the antiserum. It can be concluded that the present radioimmunoassay cannot replace the cytosol receptor assay or either supplement by measuring the 1,25(OH)₂D₃ metabolite only.

Key Words:

• antiserum
• hormone
• vitamin D₃