A New Vitamin D Deficiency Cut-Off Value in Basrah, Iraq

Abstract

Background: Vitamin D deficiency is a common health issue worldwide. Clinical observations have shown that most healthy individuals living in Iraq and the Middle East are vitamin D deficient. This study aimed to establish the true cut-off value for vitamin D deficiency (25(OH)D) in Basrah, Iraq, by analyzing the value at which parathyroid hormone (PTH) begins to rise above its reference range. Aim: This study sought to determine the true cut-off value for vitamin D deficiency (25(OH)D) in Basrah, Iraq by analyzing the value at which PTH starts to exceed its reference range. Methods: A cross-sectional study was conducted involving 874 apparently healthy subjects from Basrah, Iraq. Serum calcium, creatinine, vitamin D and PTH levels were measured for each participant. Individuals with impaired renal function and primary hyperparathyroidism were excluded from the study. The association between serum 25(OH)D and PTH was examined using multiple logistic regression analysis. The best cut-off value of serum 25(OH)D to predict elevated PTH was determined using receiver operating characteristic (ROC) analysis. Results: The mean values of 25(OH)D and PTH were 16.9 ± 14.9 ng/ml and 129.1 ± 110.5 pg/ml, respectively. If the universal cut-off values were applied, 25-hydroxyvitamin D deficiency was identified in 599 subjects (68.5%) and was inversely related to PTH. Only 139 subjects (15.9%) had optimal 25(OH)D levels. Secondary hyperparathyroidism was found in 487 subjects (45.7%). Using ROC analysis, a serum 25(OH)D value of 12.5 ng/ml was identified as the best cut-off point to predict secondary hyperparathyroidism in the population (sensitivity: 88.2%, specificity: 53.6%). The number of subjects classified as vitamin D deficient decreased to 461 (52.7%) when the new cut-off value was applied. Conclusions: The cut-off value for vitamin D deficiency needs to be redefined in areas where the disease is unexpectedly prevalent. A single cut-off value cannot be universally applied worldwide due to genetic and environmental variations. The new cut-off value is lower than that used globally. Further studies are required to establish new cut-off values.