In patients with 25(OH)D < 30 ng/mL and parathyroid hormone levels in the upper normal range or higher, we suggest administering ERC, which should be continued if secondary hyperparathyroidism is controlled; if serum parathyroid hormone levels remain persistently elevated, we suggest continuing extended-release calcifediol therapy or replacing it with a nutritional vitamin D and combining this with an active vitamin D or vitamin D analogue (Fig. 9). The gene discussed is PTH; the disease is secondary hyperparathyroidism.