A rapid and inexpensive radioimmunoassay for parathyroid hormone utilizing the Wide-principle in combination with an improved separation technique.

A radioimmunoassay of PTH which utilizes the "Wide-principle", i.e. a low concentration of antibody and a very high concentration of label, is presented. The detection limit was 0.06 micrograms/l. S-PTH in a reference group (n = 30) was 0.06-0.6 micrograms/l and the coefficient of variation was 7 and 11% at 0.8 micrograms/l (intra-day and inter-day variation). The duration of the assay is two days. The separation system involves precipitation with 20% PEG, re-suspension of the precipitate in saline followed by re-precipitation with PEG. The non-specifically bound radioactivity is reduced to 2-5%. The assay is relatively insensitive to variations in non-specifically bound radioactivity and "incubation damage". It is suitable for use in a routine laboratory for the evaluation of parathyroid gland function under various conditions. An important property of the assay is that antibody consumption is reduced, with consequent reduction in overall costs.