Parathyroid Glands response to Low Vitamin D levels in Healthy Adults: A Cross-Sectional Study

OBJECTIVE: To assess the correlation of serum parathyroid hormone (PTH) and vitamin D (25-OHD) levels based on different assays for measuring 25-OHD in healthy Saudi Arabians living along the east coast. PATIENTS AND METHODS: A cross-sectional study was conducted in 200 patients (150 women and 50 men aged between 18-69 years) between January 2011 and December 2012, attending outpatient clinic at King Fahd Hospital of the University, Al Khobar. The first 200 patients seen without vitamin D supplementation at clinic were enrolled in the study. Serum calcium, phosphorous, alkaline phosphatase, parathormone, and 25-OHD tests were performed. 25-OHD was assessed using: 1. chemiluminescence immunoassay (CLIA); 2. radioimmunoassay (RIA) using Wallac 1470 Gamma Counter. 3. HPLC –LC.MS (high performance liquid chromatography-liquid chromatography with mass spectrometry. The data was collected, entered into a database and analysed using SPSS, Inc., version 14. RESULTS: The mean age was 45.8±15.8 (18-74) years, and calcium level was 2.27±0.15 mmol/l. (range 2.125 to 2.62 mmol/l). Alkaline phosphatase was 88.91±35.94 (34-302) IU, parathormone 6.7±3.06 (1.35-21.2) (1.3-6.8 pmol/l). Of the participants, 188 were either vitamin D insufficient or deficient as measured by CLIA 11.85±6.14 (2-29.6), and 91 (48.4%) of them had secondary hyperparathyroidism 9.48±4.55 pc/l. Those with normal CLIA-measured 25-OHD levels had normal PTH levels. Of those with insufficiency, 4/21 (19%) had raised PTH levels; and of those with deficiency, 81/166 (48.79%) had raised levels, whereas with HPLC-LC.MS, 156 were shown to be insufficient and 97 deficient (with PTH level of 7.41±4.2). Thirteen of 41 patients (31.7%) with insufficiency were shown, by HPLC-LC.MS, to have raised PTH. All patients with vitamin D deficiency as diagnosed by HPLC-LC.MS had secondary hyperparathyroidism. CONCLUSIONS: The above results suggest that the method of measurement strongly influences vitamin D levels and that previous reports suggesting no association between vitamin D deficiency and secondary hyperparathyroidism should be viewed with caution.