Vitamin D [25(OH)D] and 1,25(OH)2D serum concentrations in patients tested at the Charlotte Maxeke Johannesburg Academic Hospital

Introduction: There has been a significant increase in vitamin D [25(OH)D] testing in recent years. Aims: To describe the number of tests, concentrations for 25(OH)D and 1,25(OH)2D in adults (≥ 18 years), characteristics of those tested and to determine the 25(OH)D concentration at which parathyroid hormone increases (PTH threshold). Methods: Data were extracted for 25(OH)D and 1,25(OH)2D tests, from the National Health Laboratory Services data warehouse for Charlotte Maxeke Johannesburg Academic Hospital from 2015 to 2017. Results were categorised by age, sex and race. Vitamin D status was described using National Academy of Medicine guidelines. The PTH threshold was determined by LOWESS plots. Results: 25(OH)D and 1,25(OH)2D tests increased, with no change in median concentrations over time. Black Africans (6.7%) had the highest prevalence of Vitamin D deficiency (VDD). Males had significantly lower 25(OH)D values (p < 0.001) and a higher proportion of VDD (p = 0.009). Younger patients (< 30 years; 7.9%) and elderly (> 74 years; 10.5%) black Africans had highest prevalence of VDD. The PTH threshold differed by race group. Conclusions: Clear testing guidelines are needed to curb test overutilisation. Further work is required to understand the appropriate cut-off levels to define VDD in our populations.