Methods for detecting 1,25-dihydroxyvitamin D and related antibodies

A method for detecting 1,25-dihydroxyvitamin D (1,25(OH)2D) or an analog thereof selected from one or more of the group consisting of 19-nor-1α-25-dihydroxyvitamin D2, 1α-hydroxyvitamin D2, 1α-hydroxyergocalciferol and 2-methylene-19-nor-(20S)-1α,25-(OH)2D3, in a biological fluid sample, the method comprising the steps of:

• (i) adjusting the pH of the biological fluid sample to a value comprised between 6 and 9 and simultaneously or subsequently adding to the biological fluid sample a receptor protein comprising the Ligand Binding Domain of the Rattus norvegicus Vitamin D Receptor (VDR-LBD), under conditions sufficient for forming a complex of 1,25-dihydroxyvitamin D or said analog thereof bound to the VDR-LBD of the receptor protein;
• (ii) incubating said complex in the presence of a capture moiety, wherein said capture moiety is a monoclonal antibody or a fragment of the monoclonal antibody, wherein said monoclonal antibody and said monoclonal antibody fragment comprise:
• heavy chain CDR1, CDR2, and CDR3 domains that respectively are the amino acid sequences of SEQ ID NOs:
• 1, 2 and 3;
• and
• light chain CDRs that respectively are the amino acid sequences of SEQ ID NOs:
• 4, 5 and 6;
• and
• wherein said incubation is under conditions sufficient to permit said monoclonal antibody or said monoclonal antibody fragment to bind said complex and to form a captured complex;
• and
• (iii) detecting said captured complex.