In CKD with secondary hyperparathyroidism, which change in vitamin D metabolism is typically observed?

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Multiple Choice

In CKD with secondary hyperparathyroidism, which change in vitamin D metabolism is typically observed?

Explanation:
The active form of vitamin D, 1,25-dihydroxyvitamin D (calcitriol), is decreased. In CKD, loss of healthy nephrons reduces the kidney’s ability to convert 25-hydroxyvitamin D to calcitriol via 1-alpha hydroxylase. This impairment is amplified by rising phosphate and FGF23, which further suppress 1-alpha hydroxylase and promote calcitriol breakdown. With less calcitriol, calcium absorption from the gut drops, contributing to hypocalcemia that stimulates parathyroid hormone release, driving secondary hyperparathyroidism. The other patterns—increased, unchanged, or fluctuating calcitriol—don’t fit the typical CKD/postrenal physiology, where activation of vitamin D is specifically blunted.

The active form of vitamin D, 1,25-dihydroxyvitamin D (calcitriol), is decreased. In CKD, loss of healthy nephrons reduces the kidney’s ability to convert 25-hydroxyvitamin D to calcitriol via 1-alpha hydroxylase. This impairment is amplified by rising phosphate and FGF23, which further suppress 1-alpha hydroxylase and promote calcitriol breakdown. With less calcitriol, calcium absorption from the gut drops, contributing to hypocalcemia that stimulates parathyroid hormone release, driving secondary hyperparathyroidism. The other patterns—increased, unchanged, or fluctuating calcitriol—don’t fit the typical CKD/postrenal physiology, where activation of vitamin D is specifically blunted.

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