Association of increased active PTH(1–84) fraction with decreased GFR and serum Ca in predialysis CRF patients: modulation by serum 25-OH-D

Abstract

As the serum calcium and glomerular filtration rate decreased, the proportion of active PTH(1-84) molecules in PTH immunoreactivity increased in serum from predialysis uremic patients, particularly those with vitamin D insufficiency. The PTH(1-84) fraction was altered in predialysis patients with chronic renal failure (CRF). Serum PTH in predialysis CRF patients without any medication was measured by PTH(1-84)-specific whole PTH assay and intact PTH assay cross-reacting with N-truncated PTH. In CRF patients, the glomerular filtration rate (GFR) correlated positively with serum Ca and 1,25-dihydroxyvitamin D (1,25(OH)(2)D), and inversely with serum Pi, log intact PTH, and log whole PTH. In multiple regression analysis, including age, gender, body mass index, GFR, Ca, and Pi and 1,25(OH)(2)D as independent variables, serum Ca and GFR associated significantly with serum log whole PTH and intact PTH. Serum log whole PTH/intact PTH ratio, which increased as serum Ca and GFR decreased, retained a negative correlation in those with serum 25-hydroxyvitamin D levels below 20 ng/ml, but not in those above 20 ng/ml. The ratio also correlated positively with serum log tartrate-resistant acid-phosphatase-5b, log cross-linked N-telopeptide of type-I collagen, and log bone alkaline-phosphatase. As GFR declined with suppression of serum Ca, the proportion of active PTH molecules increased in predialysis CRF patients, particularly those with vitamin D insufficiency.