Can low 25-hydroxyvitamin D with elevated calcitriol indicate thyroid autoimmunity?

A relatively low 25-hydroxyvitamin D [25(OH)D] with elevated calcitriol [1,25-dihydroxyvitamin D] is physiologically plausible but is not a diagnostic signature of thyroid autoimmunity. For a 57-year-old man, its significance depends particularly on calcium–PTH physiology, kidney function, and clinical features of systemic disease.

Mechanistic and clinical evidence

• Activated monocytes/macrophages express extrarenal CYP27B1 (1α-hydroxylase), converting circulating 25(OH)D to calcitriol outside the usual renal, PTH-regulated pathway.
• IFN-γ strongly induces this activity; TNF-α, IL-1, and IL-2 can also increase monocyte calcitriol production. Effects are context dependent—type-I interferons may inhibit hydroxylation.
• Granulomatous disease provides clinical corroboration. In sarcoidosis, macrophage calcitriol production may be PTH-independent: low 25(OH)D occurred in 64–80% of patients in two studies, whereas calcitriol was elevated in 11%. Thus, the pattern is recognized but not universal.

Differential interpretation

• Low 25(OH)D reflects reduced vitamin-D stores; elevated calcitriol does not exclude this. During vitamin-D deficiency, secondary hyperparathyroidism can preserve or raise calcitriol through increased renal conversion.
• Other established explanations include primary hyperparathyroid states, granulomatous disorders (including sarcoidosis and tuberculosis), and Hodgkin or non-Hodgkin B-cell lymphoma, potentially through tumor-associated macrophage or neoplastic calcitriol production.
• Hypercalcemia or hypercalciuria with suppressed PTH particularly raises concern for dysregulated extrarenal calcitriol production.

Bottom line

• This paired result can reflect inflammatory macrophage-driven conversion, but it is not specific for thyroid autoimmunity and should not be attributed to thyroid disease alone. Interpretation should incorporate calcium, phosphate, intact PTH, renal function, urinary calcium, vitamin-D exposure, medications, and the broader clinical assessment.