Figure 1. Sequential measurement of (upper; Y-axis is a logarithmic scale) serum levels of intact parathyroid hormone (pg/mL) and 24-h urine calcium and phosphorus (mg in 24-h urine), and (lower) serum calcium and phosphorus (mg/dL). Notably, the initial parathyroid hormone level, indicated by the downward arrow, was much lower than the levels measured after recovery. This result suggests that parathyroid hormone levels decreased immediately after CaCl2 ingestion, accompanied by increased renal calcium and decreased renal phosphorus excretion. In parallel, serum calcium and phosphorus levels gradually normalized by the fourth day of hospitalization. The normal reference ranges were as follows: 24-h urine phosphorus < 250 mg (females), 24-h urine calcium 400 - 1,300 mg, and serum intact parathyroid hormone 15 - 65 pg/mL. Reference values for serum calcium and phosphorus are shown in Table 1. Creatinine clearance, measured by 24 h urine on day 2, 3, and 6, was 41.7, 37.5, and 46.7 mL/min, respectively.