Vitamin D cutoff point in relation to parathyroid hormone: a population based study in Riyadh city, Saudi Arabia

The current recommended cutoff value for low vitamin D may result in overestimation of hypovitaminosis D. Vitamin D levels at 30.0 nmol/L can diagnose the hyperparathyroid cases leading to bone loss, with moderate accuracy, in the Saudi population. The new cutoff may help in identifying true cases that need clinical treatment and can reduce the burden on healthcare system.

Different regions of the world have reported varying cutoff points as optimal values for vitamin D status to maintain bone health.

A cross-sectional study comprising of interviews, anthropometrics, and blood samples was conducted in primary healthcare centers in Riyadh, Saudi Arabia. Standardized serum 25-hydroxyvitamin D [25(OH)D] and parathyroid hormone (PTH) were measured using electrochemiluminescence immunoassays. Independent sample and paired sample t test were conducted to compare the true means. Pearson correlation co-efficient was calculated to measure the association between original and standardized 25(OH)D. Software program, MedCalc, was utilized to measure the receiver operating curve (ROC) for determining the optimal threshold value for vitamin D.

The mean standardized 25(OH)D levels for 846 males and 1285 females were (32.0 ± 14.4 nmol/L vs 31.6 ± 16.7 nmol/L) respectively. Using the gold standard PTH cutoff > 6.9 pmol/L, the ROC had an optimal criterion value for males and females at 30.0 and 24.0 nmol/L, respectively. In the males, the sensitivity and specificity were 72% and 51%, whereas in females, it was 58.2% and 66.7%, respectively. The area under the curve (AUC) was at 0.62 and 0.65 (p < 0.001), respectively.

The recommended cutoff value for 25(OH)D for determining bone health in the Saudi population is at 30.0 nmol/L. The comparatively low cutoff point can significantly decrease the number of people diagnosed and treated with low vitamin D, which can also reduce the burden on the health care system.