The K/DOQI clinical practice guidelines recommend vitamin D therapy should be started when the intact parathyroid hormone (iPTH) exceeds 300 pg/mL in patients with secondary hyperparathyroidism. To examine whether the effect of vitamin D therapy on mineral metabolism and parathyroid gland growth varies according to the stage of secondary hyperparathyroidism and iPTH level, 47 patients with secondary hyperparathyroidism received either intravenous or pulse oral vitamin D therapy. The patients were divided into two groups based on the iPTH level at the start of vitamin D therapy: the P<300 group (N = 23) with iPTH <300 pg/mL; and the P≥300 group (N = 24) with iPTH ≥300 pg/mL. We examined serial changes in several serum mineral parameters and parathyroid gland volume and the cumulative incidence of parathyroidectomy in the first two years. Serum calcium, phosphorus, calcium-phosphorus product, and iPTH levels of the P≥300 group were significantly higher than those of the P<300 group, and could not be maintained within the target ranges set by the K/DOQI guidelines. In contrast, the serum levels of phosphorus, calcium-phosphorus product, and iPTH were maintained within the target ranges and the parathyroid gland did not enlarge in the P<300 group. The cumulative incidence of parathyroidectomy in the P≥300 group was significantly higher than in the P<300 group. Early intervention with intravenous or pulse oral vitamin D therapy at serum iPTH <300 pg/mL can control serum phosphorus, calcium-phosphorus product, and PTH levels to the target ranges and slow the progression of secondary hyperparathyroidism.
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