Clinical Utility of Measurement of Vitamin D-Binding Protein and Calculation of Bioavailable Vitamin D in Assessment of Vitamin D Status

Abstract

BackgroundThe associations of vitamin D deficiency with various clinical conditions highlighted the importance of vitamin D testing. Currently, clinicians measure only the total 25-hydroxyvitamin D [25(OH)D] concentration, regardless of its bioavailability. We aimed to determine the effect of vitamin D-binding protein (VDBP) on 25(OH)D bioavailability.MethodsSerum samples were collected from 60 healthy controls, 50 pregnant women, and 50 patients in intensive care units (ICUs). Total 25(OH)D was quantified by liquid chromatography with tandem mass spectrometry, and VDBP levels were determined by using an ELISA kit (R&D Systems, USA). The bioavailable 25(OH)D levels were calculated by using total 25(OH)D, VDBP, and albumin concentrations.ResultsIn comparison with healthy controls, the total 25(OH)D concentration was significantly lower in ICU patients (median, 11.65 vs 18.25 ng/mL; P<0.00001), but no significant difference was noted between pregnant women (18.25 ng/mL) and healthy controls. The VDBP level was significantly lower in ICU patients (95.58 vs 167.18 µg/mL, P=0.0002) and higher in pregnant women (225.01 vs 167.18 µg/mL, P=0.008) compared with healthy controls. Nonetheless, the calculated bioavailable 25(OH)D levels of ICU patients and pregnant women were significantly lower than those of healthy controls (1.97 and 1.93 ng/mL vs 2.56 ng/mL; P=0.0073 and 0.0027).ConclusionsA single marker of the total 25(OH)D level is not sufficient to accurately evaluate vitamin D status, especially in pregnant women. In cases where VDBP concentrations may be altered, VDBP measurements and bioavailable 25(OH)D calculations may help to determine vitamin D status accurately.

Alterations in the vitamin D endocrine system during pregnancy: A longitudinal study of 855 healthy Norwegian women

“…Through the vitamin D receptor, regulates 1,25(OH) 2 D hundreds of genes in a variety of body tissues [ 6 , 14 , 19 , 20 ]. A major proportion of 25(OH)D and 1,25(OH) 2 D binds to vitamin D-binding protein (DBP) or albumin (>99%) [ 21 , 22 ]. Free and bioavailable fractions seem to be more strongly correlated to the biological activity [ 14 , 22 – 24 ].…”

“…Free and bioavailable fractions seem to be more strongly correlated to the biological activity [ 14 , 22 – 24 ]. Serum levels of 25(OH)D are used for evaluation of vitD status [ 3 , 14 , 15 , 21 ]. The optimal levels of 25(OH)D and 1,25(OH) 2 D during pregnancy are, however, not settled, and recommendations concerning vitD intake are diverging [ 4 – 6 , 14 , 17 , 25 ].…”

“…A large variation in 1,25(OH) 2 D levels in third trimester has also been observed [ 18 ]. Larger longitudinal studies concerning 1,25(OH) 2 D, free and bio-available vitamin D in pregnancy are scarce [ 18 , 21 , 23 ].…”

DGEM-Leitlinie: „Klinische Ernährung in der Intensivmedizin“

“…Prähospital erniedrigte 25-Hydroxy-Vitamin-D-Konzentrationen sind mit einer erhöhten Gefahr von Bakteriämien [435] und einer erhöhten Krankenhausmortalität assoziiert [436, 437]. Bei kritisch kranken Patienten ist zu einem großen Teil die 25-Hydroxy-Vitamin-D-Konzentration, die 1,25-Dihydroxy-Vitamin-D-Konzentration und das Vitamin-D-bindende Protein erniedrigt[433,438]. Eine Pharmakotherapie mit 250 000 IU bzw.…”

Association between Vitamin D Level and Muscle Strength in Patients Undergoing Hemodialysis

“…Measurements using electrochemiluminescent immunoassay would lead to underestimation of 25-OH vitamin D levels compared with radioimmunoassay or liquid chromatographytandem mass spectrometry [35,36]. In addition, 25-OH vitamin D level alone does not reflect the exact bioavailability, and a combination of recent methods such as vitamin D-binding protein level may help to represent the vitamin D status [37]. Third, our study did not include sufficient biomarkers of inflammation, which are associated with vitamin D deficiency.…”