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Variations in Parathyroid Hormone Concentrations in Patients with Low Vitamin D – June 2012

Endocr Rev, Vol. 33 (03_MeetingAbstracts): MON-383
Copyright © 2012 by The Endocrine Society ENDO 2012: June 23-26, 2012, Houston, Texas
Bhanu T Paturi, MD 1 and Amal S Rahhal, MD 1
1 Endocrinology, Diabetes and Metabolism, University of Iowa Hospitals and Clinics Iowa City, IA

In Vitamin D deficiency parathyroid hormone starts increasing when the 25 hydroxyvitamin D (25OHD) drops below 30 ng/dl and PTH is often used to define vitamin D sufficiency. However in clinical practice, we have observed that the PTH is not always elevated in patients with low vitamin D levels and that the time to PTH normalization after correction of vitamin D deficiency varies widely between patients. The objective of this study was to examine variations in PTH levels in patients with low vitamin D levels and to examine how PTH levels changed following correction of the vitamin D deficiency.We conducted a retrospective cohort study of all adults (age 18 years) with a 25OHD level < 30 ng/ml seen in our clinic at the University of Iowa over a four year period. We excluded patients with no available baseline PTH values, as well as patients with concomitant conditions that may be associated with abnormal PTH levels, including abnormal kidney function (GFR<60), hypercalcemia, hyperparathyroidism, hypoparathyroidism and rickets. We then examined variability in baseline PTH levels and the changes in PTH after correction of the vitamin D deficiency/insufficiency. The mean age of our cohort was 55.5 years, mean daily calcium intake was 1002.8 mg, 25OHD- 20.5 ng/ml, PTH-59.8 pg/ml. After treatment with vitamin D (average duration 10 months), the mean 25OHD increased from 20.5 to 40.7 ng/ml (p < 0.01) and the mean PTH decreased from 59.8 to 56.2 pg/ml (p 0.04). 73 patients (70% of the cohort) had a normal PTH concentration at baseline. Patients with a normal baseline PTH did not experience a significant change in their PTH after normalization of the 25OHD. However, in patients with an elevated baseline PTH, the PTH level decreased from 103.3 to 72.3 pg/ml after normalization of the 25 OHD (p 0.03). Of the 31 patients who had an elevated PTH at baseline, follow up data was available on 22. Only10 patients (45.5%) experienced immediate normalization of the PTH as their 25OHD increased above 30 ng/dl, while the PTH remained elevated in the rest for up to 2 years.In this group of patients with a 25OHD concentration < 30 ng/dl, up to 70% had a normal baseline PTH level.

In patients with an elevated baseline PTH, the hyperparathyroidism seems to "lag behind" correction of the vitamin D status in more than 50 % of the patients.

These findings suggest that PTH may not be helpful in defining vitamin D "sufficiency" and guiding vitamin D therapy in clinical practice.

Nothing to Disclose: BTP, ASR
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See also VitaminDWiki

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