Direct detection of free vitamin D as a tool to assess risk conditions associated with chronic plaque psoriasis

INTRODUCTION: Psoriasis is a major public health problem that results in high social and health costs. New approaches and methods are required to identify any conditions related to the disease and comorbidity development. The vitamin D deficiency is associated to psoriasis and could play an important role in its pathogenesis. However, the serum level of vitamin D is currently measured as total vitamin D, which is affected by wide variability. Therefore, the determination of the free form could be more significant, since it is independent of confounding factors. A cross-sectional study was performed to assess the association between chronic plaque psoriasis and serum level of free vitamin D, detected by a direct analytical method. METHODS: The levels of bioavailable vitamin D, total vitamin D and other metabolic parameters whose homeostasis is regulated by vitamin D were evaluated in 72 psoriasis patients and in 48 healthy controls. A direct immunoassay method was used to measure serum free vitamin D level. Analysis of covariance was performed to calculate estimated marginal means (EMM) and 95% confidence interval (CI), after adjustment for age, sex and BMI, within the two groups. RESULTS: Patients showed an EMM of 5.526 ± 0.271pg/ml, 95% CI 4.989-6.063; while controls an EMM of 6.776 ± 0.271 pg/ml, 95% CI 6.115-7.437. CONCLUSIONS: Chronic plaque psoriasis patients exhibited a serum level of free vitamin D lower than controls. The direct immunoassay method could represent a useful tool to assess vitamin D status and identify a risk condition associated with the onset of the pathology.