Background and Objectives: The low vitamin D status in an individual leads to a compensatory increase in serum parathyroid hormone (PTH) level giving rise to secondary hyperparathyroidism. The elevated PTH will conserve calcium excretion from the kidneys in the expense of excreting phosphate. Thus, serum calcium levels tend to remain normal until the latter stages of vitamin D deficiency. PTH action on the bone to reabsorb more calcium from the bone lead to elevation of bone alkaline phosphatase (ALP) in the serum. Nevertheless, population screening for vitamin D deficiency in asymptomatic individuals is currently not recommended. ALP measurement as a screening test to detect vitamin D deficiency is a relatively inexpensive test that can be performed easily. We have studied the relationship between the ALP, calcium, phosphate and PTH level to the vitamin D status of patients attending the NHSL.
Methods: A descriptive cross sectional study was conducted from March/2019 to March/2020 at the Endocrinology Unit of the National Hospital of Sri Lanka. Consecutive sampling was done recruiting all patients who have had vitamin D assessment as part of the routine medical care. Interviewer administered questionnaire was used collect data. Vitamin D sufficiency, insufficiency and deficiency was defined on levels of >50 ng/ml, 2050 ng/ml, <20 ng/ml respectively. Pearson correlation analysis was used to determine the effects of vitamin D status on various blood parameters including serum total calcium, serum phosphate, ALP and PTH level. Receiver operating characteristic (ROC) curves were used to determine the optimal ALP level to predict vitamin D deficiency.
Results: 153 subjects who meets the inclusion and exclusion criteria were recruited in to the study over a period of one year. The population mean age was 52.1 (S.D. ±14.38) years and ranged from 18 to 89 years. Out of the whole population 58.8% had vitamin D deficiency while 31.4% suffered from vitamin D insufficiency. Only 9.8% had normal vitamin D levels. ALP level was significantly related to vitamin D deficiency (P<0.05). At ALP cutoff value of 72.5 U/L the vitamin D deficiency could be predicted with 76% sensitivity and 80% specificity. ALP cutoff 43 U/L predicts vitamin D deficiency at a 100% sensitivity and 20% specificity.
Conclusions: The population screening for vitamin D deficiency is not a cost effective intervention. A more cheaper and feasible ALP assessment at a cutoff value of 72.5 U/L can predict vitamin D deficiency at a significantly higher specificity and sensitivity.
