A sensitive radioimmunoassay using a monoclonal antibody that is equipotent for ercalcitriol and calcitriol (1,25-dihydroxy vitamin D2 and D3)

Clin Chim Acta. 1990 Oct 15;190(3):199-209. doi: 10.1016/0009-8981(90)90174-q.


A monoclonal antibody has been used in a sensitive radioimmunoassay that measures 1,25-dihydroxyvitamin D2 (ercalcitriol) and 1,25-dihydroxyvitamin D3 (calcitriol) with equal potency. This important characteristic has not been reported for any other radioimmunoassay for 1,25-dihydroxyvitamin D. The two forms can be assayed in human serum together or individually after HPLC separation. Sample preparation entails acetonitrile extraction followed by C18-Sep-pak chromatography and HPLC. The assay measures 98% of added analyte, and achieves inter- and intra-assay coefficients of variation of 10.7% at 34 pg/ml and 7.8% at 81 pg/ml respectively. The limit of detection is 1.25 pg/tube and 50% displacement of bound ligand is achieved at 14 pg/tube. The reference interval is 20-50 pg/ml, mean 35. The correlation between results from the monoclonal radioimmunoassay and an established polyclonal antibody method was r = 0.98, slope 0.99. The assay has particular application in patients treated with vitamin D2 since 1,25-dihydroxyvitamin D2 can now be measured accurately in the presence of 1,25-dihydroxyvitamin D3.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Monoclonal
  • Calcitriol / blood*
  • Chromatography, High Pressure Liquid
  • Ergocalciferols / administration & dosage
  • Ergocalciferols / blood*
  • Ergocalciferols / therapeutic use
  • Humans
  • Microchemistry
  • Radioimmunoassay* / standards
  • Radioimmunoassay* / statistics & numerical data
  • Reference Values
  • Seasons
  • Vitamin D Deficiency / blood
  • Vitamin D Deficiency / drug therapy


  • Antibodies, Monoclonal
  • Ergocalciferols
  • 1,25-dihydroxyergocalciferol
  • Calcitriol