A sensitive radioimmunoassay using a monoclonal antibody that is equipotent for ercalcitriol and calcitriol (1,25-dihydroxy vitamin D2 and D3).
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.
Mawer
E B
EB
Department of Medicine, University of Manchester Medical School, UK.
Berry
J L
JL
Cundall
J P
JP
Still
P E
PE
White
A
A
D000911:Antibodies, Monoclonal; D002117:Calcitriol / Q000097:blood*; D002851:Chromatography, High Pressure Liquid; D004872:Ergocalciferols / Q000008:administration & dosage / Q000097:blood* / Q000627:therapeutic use; D006801:Humans; D008832:Microchemistry; D011863:Radioimmunoassay / Q000592:standards / Q000706:statistics & numerical data; D012016:Reference Values; D012621:Seasons; D014808:Vitamin D Deficiency / Q000097:blood / Q000188:drug therapy
D000911:Antibodies, Monoclonal; D004872:Ergocalciferols; C003564:1,25-dihydroxyergocalciferol; D002117:Calcitriol