SAT176 Comparison Of Prevalence For Normocalcemic Primary Hyperparathyroidism (NPHPT) Using Different 25(OH)D Levels: A Systematic Review

Abstract Disclosure: I.N. Farooqi: None. X. Wang: None. The familiar topic of vitamin D deficiency remains controversial in the context of bone metabolism and health, with findings supportive of differing thresholds for supplementation. While the Fifth International Workshop has not delineated exact cutoffs for 25(OH)D to rule out the secondary cause of vitamin D deficiency in evaluations of NPHPT, we believe higher thresholds will yield fewer rates of diagnosis. We postulate that a review of existing literature yields significant differences in the reported prevalence of NPHPT when comparing 25(OH)D cutoffs of ≥30ng/mL versus ≥20ng/mL. PubMed searches were conducted using the key words “normocalcemic primary hyperparathyroidism,” “prevalence,” “trial,” and 7400 studies were initially found. Excluding studies from before 2010, those using population sizes less than 100 subjects, and abstracts, we found a total of 14 articles for which full-text review was performed. We examined 9 studies using the 25(OH)D cutoff ≥20ng/mL and 5 studies using ≥30ng/mL for our analysis. Although research on NPHPT has been done worldwide, including Europe, East Asia, North and South Americas, none were found in Africa, South Asia, and Australia. Our review identified 9/14 studies in Canada, USA, UK, Sweden, Czech Republic, Italy, Belgium, and China which used 25(OH)D ≥20ng/mL to exclude vitamin D deficiency, with a prevalence range of 0.18-21%, averaging 5.81%. Conversely, the remaining 5/14 studies from Brazil, USA, Spain, and Italy using ≥30ng/mL as the lower limit of 25(OH)D for diagnosing NPHPT yielded prevalence rates ranging 0.02-8.9% with an average of 3.17%. The prevalence of NPHPT is 8.9% in the Brazilian study by Marques et al. in 2011 and 6% in the Spanish study by Garcia-Martin in 2012, while the remainder of North American and European studies using the ≥30ng/mL cutoff from 2015 onward reported prevalence rates of only 0.02-0.6%. Of the total number of publications reviewed since 2015, 30% of the studies implemented the higher threshold of ≥30ng/mL. Previously documented prevalence rates of NPHPT among healthy adults have used 25(OH)D ≥20ng/mL to define the exclusion of vitamin D deficiency; however, our current review of several studies since 2010 demonstrates a significantly lower prevalence of the disease when the cutoff is raised to ≥30ng/mL. Our findings suggest greater specificity in the exclusion of vitamin D deficiency in more recent publications. Recent research examining free 25(OH)D as a more effective marker for vitamin D status suggests total 25(OH)D ≥30ng/mL may still be insufficient to completely exclude vitamin D deficiency in NPHPT. Thus, the role of varying 25(OH)D cutoffs is interesting and requires further investigation on a geographic level, as it may provide more insight into interethnic variations, correlation with seasonality and sunlight exposure, and healthcare access in regions where such studies have yet to be conducted. Presentation: Saturday, June 17, 2023

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