Measuring vitamin D levels: surrogates are insufficient.

Area of Science:

• Clinical Biochemistry
• Endocrinology
• Nutritional Science

Background:

• Growing evidence links low vitamin D levels to adverse health outcomes.
• Increased demand for vitamin D screening necessitates efficient diagnostic methods.

Purpose of the Study:

• To evaluate the adequacy of parathyroid hormone (PTH) and bone profile markers in identifying vitamin D insufficiency or deficiency.
• To determine if direct measurement of 25-hydroxyvitamin D (25-OH vitamin D) is necessary.

Main Methods:

• Analysis of 1560 serum specimens for 25-OH vitamin D, calcium, phosphate, alkaline phosphatase (ALP), creatinine, and PTH.
• Specimens were collected from November 2010 to November 2012.

Main Results:

• The prevalence of vitamin D insufficiency or deficiency (25-OH vitamin D < 50 nmol/l) was 62.9%, with higher rates in males.
• While low vitamin D correlated with lower phosphate levels, a significant proportion of deficient patients had normal PTH, calcium, phosphate, and ALP levels.
• Even with severe deficiency (25-OH vitamin D < 10 nmol/l), many patients exhibited normal PTH and bone profile markers.

Conclusions:

• No surrogate marker, including PTH and bone profile tests, is sufficient for screening vitamin D deficiency.
• Direct measurement of 25-OH vitamin D is essential for accurate diagnosis despite associated costs.