Method for obtaining an antibody or antibody fragment to a conformational epitope specific for oxidized, inactive human parathyroid hormone and fragments thereof; a method for removal of oxidized, inactive human parathyroid hormone from a sample of body fluid; methods of determining the concentration of active parathyroid hormone in a sample, and an in vitro method of diagnosis of renal failure or secondary hyperthyroidism in patients on dialysis. The antibody is obtained by immunizing an animal with an immunogen containing parathyroid hormone or fragment thereof oxidized at methionines at positions 8, 18 or both; and a recovering of antibodies; whereby the complementary determining region of the antibody or antibody fragment or single chain antibody specifically recognizes a conformational epitope (antigenic determinant) which is a tertiary structure and only present on oxidized parathyroid hormone and fragments thereof only but not regular bioactive human parathyroid hormone, while the binding surface to the complementary binding region does not include any one of the oxidized methionines of human parathyroid hormone.