Vitamin D Binding Protein (DBP), Free Calcidiol, and Total Calcitriol in Adults from Northern Greece

An ongoing debate has been raised on whether is better to use total or free calcidiol as a screening test in the population.

In winter and summer, free calcidiol, total calcitriol, and vitamin D binding protein (DBP) concentrations were determined by immunoenzymatic assays in 326 adults (161 males, 165 females). These included 99 osteoporotic patients, 53 type 1 and 51 type 2 diabetics, and 123 athletic healthy persons, all from northern Greece.

In the whole sample, free calcidiol mean concentrations differed significantly (p < 0.001) between males (5.53 pg/ml) and females (4.68 pg/ml). Free calcidiol was significantly greater in the athletic healthy group (6.02 pg/ml) than in the three patient groups, and lowest in the osteoporosis group (3.69 pg/ml). Total calcitriol mean concentration did not differ significantly between genders in the whole sample (p = 0.896) or in the study groups, except for type 2 diabetics (males 38.33 pg/ml, females 54.52 pg/ml, p = 0.001). It was significantly less in the osteoporotics (34.61 pg/ml) than in the athletic healthy group (41.65 pg/ml, p = 0.037) and type 1 diabetics (43.73 pg/ml, p = 0.030), whereas it did not differ significantly between the other study groups. The DBP mean concentrations were not significantly different between genders in the whole sample and the study groups nor among the study groups (p = 0.467).

Comparisons with our previously reported results of total calcidiol suggest the measurement of free calcidiol offers nothing more than that, and total calcitriol is not a sensitive measure for assessing vitamin D status.