Glomerular Filtration Rate Is a Major Determinant of the Relationship between 25-Hydroxyvitamin D and Parathyroid Hormone
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- Patel, S., Hyer, S. & Barron, J. Calcif Tissue Int (2007) 80: 221. doi:10.1007/s00223-007-9001-9
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The reference range for 25-hydroxyvitamin D (25-OHD) remains uncertain, and it is not clear as to whether interpretation of circulating 25-OHD would be aided by simultaneous measurement of serum parathyroid hormone (PTH). We wanted to define the level of serum 25-OHD associated with a raised serum PTH and to examine the determinants of the relationship between serum 25-OHD and serum PTH concentration. We retrospectively examined data for patients who had a 25-OHD measurement and other biochemical variables over a 12-month period in our center. We found that 28% of patients had a serum 25-OHD level below 50 nmol/L and serum PTH level in the normal reference range, whereas 24% had a serum 25-OHD level below 50 nmol/L with a serum PTH value above the normal reference range. At a serum 25-OHD level of 80 nmol/L, 1.5% had an elevated serum PTH and, at 50 nmol/L, 8% had raised serum PTH. Further examination showed that for patients with low serum 25-OHD, low glomerular filtration rate (GFR) was a major determinant of the PTH response. These data confirm an inverse correlation between serum 25-OHD and serum PTH. Minimal numbers of patients (1.5% of the study group) have a raised serum PTH at a serum 25-OHD level of 80 nmol/L. GFR is a major determinant of the PTH response to decreasing serum levels of 25-OHD.