QuestAssureD 25-Hydroxy and Calcitriol 1,25-Dihydroxyvitamin D

This panel measures two different forms of vitamin D in your blood to give a complete picture of how your body is storing and using vitamin D. The first form (25-OH D) tells your doctor how much vitamin D you have stored in your body, which depends on your diet, sun exposure, and supplements. The second form (1,25-dihydroxyvitamin D) is the active version that your kidneys make and that actually does the work in your body, such as helping absorb calcium and keeping your bones strong. Having both results together helps your doctor understand not just whether you have enough vitamin D, but also whether your body is processing it correctly. Abnormal results in either direction can have health implications and should be discussed with your healthcare provider.

When elevated: Elevated 25-OH D may indicate vitamin D toxicity or excessive supplementation, potentially leading to hypercalcemia and soft tissue calcification. Elevated 1,25-dihydroxyvitamin D can indicate ectopic calcitriol production (as seen in granulomatous diseases such as sarcoidosis, tuberculosis, or lymphoma), primary hyperparathyroidism, or certain vitamin D-dependent conditions; this can cause hypercalcemia and hypercalciuria independent of 25-OH D levels. When low: Low 25-OH D indicates insufficient vitamin D stores, associated with increased risk of metabolic bone disease, secondary hyperparathyroidism, muscle weakness, and impaired immune function. Low 1,25-dihydroxyvitamin D in the context of adequate 25-OH D suggests impaired renal activation, as seen in chronic kidney disease, hypoparathyroidism, or pseudohypoparathyroidism, and may contribute to hypocalcemia and renal osteodystrophy.

Vitamin D supports calcium absorption for bone health under training load, immune function during heavy training blocks, and may influence muscle protein synthesis and recovery. Athletes with limited sun exposure or indoor training schedules benefit from tracking both metabolites to catch deficiency that active form alone might miss.