Serum levels of 3-epi-25-OH-D3 during hypervitaminosis D in clinical practice

Intoxication from vitamin D supplements has been rarely reported, but nowadays, it occurs more frequently. The presence of the C-3 epimer of 25-hydroxyvitamin D(3) (3-epi-25-OH-D(3)) is highly prevalent in adults, although there is little information regarding its in vivo relevance, if any, especially under pathological conditions.

Our aim was to assess the presence of the 3-epi-25-OH-D(3) in serum samples displaying 25-OH-D(3) concentrations indicative of hypervitaminosis D.

A total of 58 samples displaying a wide range of concentrations of 25-OH-D(3) (>64-439 ng/ml) by ultrafast liquid chromatography were consecutively recruited and reassessed for the presence of 3-epi-25-OH-D(3) using a second chromatographic system. Data from additional biochemical tests performed as part of the patient evaluation were also recorded.

Mean relative contribution of 3-epi-25-OH-D(3) was less than 4%, and concentrations ranged from 2-28.6 ng/ml. Serum levels of the C3 epimer, but not the relative contribution, correlate with serum 25-OH-D(3). Overall, in subjects with 25-OH-D(3) concentrations indicative of hypervitaminosis D, the presence of the C-3 epimer and its levels were apparently unrelated to age, serum markers of renal and liver function, acute-phase reactants, and the presence of hypercalcemia. 3-Epi-25-OH-D(3) did not correlate with PTH, but subjects displaying PTH suppression (<14 pg/ml) showed higher concentrations of 3-epi-25-OH-D(3).

The relative contribution of 3-epi-25-D(3) was not significantly altered during hypervitaminosis D, although the absolute levels reached in serum may be biologically relevant. From a clinical viewpoint, although the small size of the group may affect the lack of relationships, the presence of 3-epi-25-OH-D(3) was apparently unrelated to serum markers of renal and liver function, acute-phase reactants, PTH, and the presence of hypercalcemia.