Abstract
BackgroundInterpretation of parathyroid hormone (iPTH) requires knowledge of vitamin D status that is influenced by season.ObjectiveCharacterize the temporal relationship between 25-hydroxyvitamin D3 levels [25(OH)D3] and intact iPTH for several seasons, by gender and latitude in the U.S. and relate 25-hydrovitamin D2 [25(OH)D2] levels with PTH levels and total 25(OH)D levels.MethodWe retrospectively determined population weekly-mean concentrations of unpaired [25(OH)D2 and 25(OH)D3] and iPTH using 3.8 million laboratory results of adults. The 25(OH)D3 and iPTH distributions were normalized and the means fit with a sinusoidal function for both gender and latitudes: North >40, Central 32–40 and South <32 degrees. We analyzed PTH and total 25(OH)D separately in samples with detectable 25(OH)D2 (≥4 ng/mL).FindingsSeasonal variation was observed for all genders and latitudes. 25(OH)D3 peaks occurred in September and troughs in March. iPTH levels showed an inverted pattern of peaks and troughs relative to 25(OH)D3, with a delay of 4 weeks. Vitamin D deficiency and insufficiency was common (33% <20 ng/mL; 60% <30 ng/mL) as was elevated iPTH levels (33%>65 pg/mL). The percentage of patients deficient in 25(OH)D3 seasonally varied from 21% to 48% and the percentage with elevated iPTH reciprocally varied from 28% to 38%. Patients with detectable 25(OH)D2 had higher PTH levels and 57% of the samples with a total 25(OH)D > 50 ng/mL had detectable 25(OH)D2.Interpretation25(OH)D3 and iPTH levels vary in a sinusoidal pattern throughout the year, even in vitamin D2 treated patients; 25(OH)D3, being higher in the summer and lower in the winter months, with iPTH showing the reverse pattern. A large percentage of the tested population showed vitamin D deficiency and secondary hyperparathyroidism. These observations held across three latitudinal regions, both genders, multiple-years, and in the presence or absence of detectable 25(OH)D2, and thus are applicable for patient care.
Highlights
Parathyroid hormone (PTH) concentrations are known to have a reciprocal seasonal relationship with 25(OH)D in studies lasting up to a year [1,2,3,4,5]
We investigated the seasonal variation of 25(OH)D and Interpretation of parathyroid hormone (iPTH) over a multi-year period using data drawn from a large clinical data base comprising results from more than 3.8 million patients from throughout the continental United States who sought laboratory testing for 25(OH)D or iPTH
The study included 2,274,884 25(OH)D3 results and 1,529,289 iPTH results, performed as routine care, for patients of both genders, spanning the ages of 20 to 99 years, living within the continental United States, from January 2007 through December 2009 in the Quest Diagnostics database. 7% of patients had a diagnosis of vitamin D deficiency (ICD-9 code 268.9) were included
Summary
Parathyroid hormone (PTH) concentrations are known to have a reciprocal seasonal relationship with 25(OH)D in studies lasting up to a year [1,2,3,4,5]. Krall et al and Tangpricha et al demonstrated an inverse relationship between parathyroid hormone and 25(OH)D3 over one season [3,4]. Studies limited to one year in duration are insufficient to characterize the recurrent temporal relationship. To avoid these limitations, we investigated the seasonal variation of 25(OH)D and iPTH over a multi-year period using data drawn from a large clinical data base comprising results from more than 3.8 million patients from throughout the continental United States who sought laboratory testing for 25(OH)D or iPTH. Interpretation of parathyroid hormone (iPTH) requires knowledge of vitamin D status that is influenced by season
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