Parathyroid Hormone Test Interactions

Vitamin D supplementation does not chemically interfere with the parathyroid hormone (PTH) assay itself, but it physiologically suppresses PTH secretion by raising serum 25-hydroxyvitamin D and calcium levels. A PTH drawn after starting or adjusting vitamin D can therefore look lower than the patient's true baseline, complicating workup of suspected primary hyperparathyroidism or vitamin D deficiency.