Blood specimens were obtained in a standardized fashion in the morning, after at least 12 h of fasting and 30 min of resting in a supine position in a quiet, environmentally controlled room. Fasting morning urinary samples and 24-h urinary samples were collected. The serum PTH levels were determined using Elecsys PTH (1–84) test (Cobas®, Roche Diagnostics GmbH, Germany). Vitamin D (25(OH)D3) levels were measured using the LIAISON test (DiaSorin Inc., USA). To calculate [Ca]alb and [Ca2+]pH, we used the standard formulas [14 (link), 15 (link)].
The laboratory calibration references for Ca-P metabolism parameters were as follows: [Ca]alb. (serum), 2.19–2.54 mmol/L; [Ca2+]pH (serum), 1.13–1.32 mmol/L; daily urinary Ca secretion, 2.5–6.25 mmol/24 h (females) and 3.75–7.5 mmol/24 h (males); phosphates (serum), 0.9–1.5 mmol/L; phosphates (urine), 40–136 mg/dL; daily urinary phosphate secretion, 0.4–1.3 g/24 h; PTH (serum), 10–65 pg/mL; and 25(OH)D3, 30–80 ng/mL.
The laboratory calibration references for Ca-P metabolism parameters were as follows: [Ca]alb. (serum), 2.19–2.54 mmol/L; [Ca2+]pH (serum), 1.13–1.32 mmol/L; daily urinary Ca secretion, 2.5–6.25 mmol/24 h (females) and 3.75–7.5 mmol/24 h (males); phosphates (serum), 0.9–1.5 mmol/L; phosphates (urine), 40–136 mg/dL; daily urinary phosphate secretion, 0.4–1.3 g/24 h; PTH (serum), 10–65 pg/mL; and 25(OH)D3, 30–80 ng/mL.