Endocrine Abstracts

Background: Adequate vitamin D supply is necessary for bone metabolism and also for the general maintenance of health. 25OHD is transported primarily bound to vitamin-D binding protein (DBP), but also to albumin. Lower concentration of plasma proteins may cause difficulties in immunoanalytics. Our aim was to investigate the protein dependence of the two most often used 25OHD immuno- (CLIA) and protein binding- (ECLPBA) assays.

Methods: levels were measured by CLIA and ECLPBA. Exogenous albumin was added by in vitro experiment at five dilution steps to serum pools from patients (N=24) with low albumin while DBP remained permanent. 109 clinical cases were investigated too, 63 patient with subnormal albumin levels (with cirrhosis, nephrosis, malabsorption syndrome, chronic renal failure), and 46 healthy control with normal albumin levels.

Results: In the in vitro experiment the bias of 25OHD was markedly positive by increasing concentrations of albumin in case of ECLPBA. By the CLIA the bias of 25OHD was mostly slight and negative. Patient’s sera with low albumin showed significantly lower 25OHD levels compared to specimens with higher albumin levels by both methods. Analyzing the obtained concentrations of 25OHD between two methods there was no difference in controls, but it was significant in hospitalised patients. Among clinical subgroups, there were no significant differences between the two methods except cirrhosis.

Conclusion: Our results suggest that CLIA method interact more with DBP and less with albumin, than the ECLPBA. Both 25OHD methods depend somewhat on albumin levels, but it is only marginal in sera with normal albumin levels, but characteristic with lower albumin. Our results call attention to the fact that each method showed a proportionate 25OHD vitamin level change in accordance with the changing albumin levels and DBP/albumin ratio.