Association of serum intact parathyroid hormone with lower estimated glomerular filtration rate

Background and objectives: The prevalence of mineral metabolism abnormalities is almost universal in stage 5 chronic kidney disease (CKD), but the presence of abnormalities in milder CKD is not well characterized. Design, setting, participants, & measurements: Data on adults ≥20 yr of age from the National Health and Nutrition Examination Survey 2003-2004 (N = 3949) were analyzed to determine the association between moderate declines in estimated GFR (eGFR), calculated using the Modfication of Diet in Renal Disease formula, and serum intact parathyroid hormone (iPTH) ≥ 70 pg/ml. Results: The geometric mean iPTH level was 39.3 pg/ml. The age-standardized prevalence of elevated iPTH was 8.2%, 19.3%, and 38.3% for participants with eGFR ≥ 60, 45 to 59, and 30 to 44 ml/min/1.73 m², respectively (P-trend < 0.001). After adjustment for age; race/ethnicity; sex; menopausal status; education; income; cigarette smoking; alcohol consumption; body mass index; hypertension; diabetes mellitus; vitamin D supplement use; total calorie and calcium intake; and serum calcium, phosphorus, and 25-hydroxyvitamin D levels - and compared with their counterparts with an eGFR ≥ 60 ml/min/1.73 m² - the prevalence ratios of elevated iPTH were 2.30 and 4.69 for participants with an eGFR of 45 to 59 and 30 to 44 ml/min/1.73 m², respectively (P-trend < 0.001). Serum phosphorus ≥ 4.2 mg/dl and 25-hydroxyvitamin D < 17.6 ng/ml were more common at lower eGFR levels. No association was present between lower eGFR and serum calcium < 9.4 mg/dl. Conclusions: This study indicates that elevated iPTH levels are common among patients with moderate CKD.