Means and methods of measuring parathyroid hormone in patients suffering from oxidative stress

A method for measuring an active parathyroid hormone level in a sample of body fluid comprising the steps of

• (i) screening antibodies that specifically bind inactive human parathyroid hormone (hPTH) peptides and circulating inactive hPTH fragments thereof, the screening comprising
• a) obtaining antibodies against human parathyroid hormone peptide by immunizing a non-human animal with an immunogen comprising as hapten oxidized parathyroid hormone or an oxidized fragment of parathyroid hormone, and recovering said antibodies from said non-human animal;
• b) selecting or purifying said antibodies from antibody molecules that bind to bioactive human parathyroid hormone peptide under physiological conditions to obtain antibodies that specifically recognize oxidized parathyroid hormone or fragments thereof;
• and
• c) selecting or purifying said antibodies against oxidized parathyroid hormone by their binding to an hPTH amino acid sequence (primary protein structure) comprising at positions 8, 18 or both methionine R-sulfoxide, methionine L-sulfoxide or methionine sulfone, to select or obtain antibody molecules having a CDR that specifically binds to a conformational epitope (tertiary protein structure) of oxidized or inactive human parathyroid hormone peptides;
• (ii) contacting the sample with a solid phase or slurry to which are bound said screened antibodies, and
• (iii) measuring the concentration of parathyroid hormone in the sample for determining the level of active hPTH.