Abstract
The present study was designed to completely reevaluate serum iPTH in the osteoporosis of aging and its relationship to aging in normal subjects. The results are entirely consistent with those of the authors. Mean serum iPTH was lower in osteoporotic than in control subjects with all three radioimmunoassays. Serum iPTH was increased greater than 3 S.D. above age-matched control values in 8% of the osteoporotic patients with the carboxyl-region specific assay and at the upper limits of normal in the same patients with the assay which measures "intact" PTH. In confirmation of the studies of Roof et al. and of Wiske et al., serum iPTH increased with age from 20-90 years in control subjects. This increase was 80% with the carboxyl-region specific assay but only 30% with the assay specific for intact PTH suggesting that there is a relatively greater increase in circulating, biologically inactive, carboxyl-region PTH fragments than there is an increase of biologically active intact PTH with age.