The prevalence of vitamin deficiency in clinical practice is assay-dependent.
OBJECTIVE
Vitamin D deficiency is an important concern in clinical settings and recently, international agencies have recognised the importance of 25-OHD assays in defining vitamin D status. Thus, our aim was to assess the consistency of different vitamin D assays in clinical practice.


METHODS
25-OH-vitamin D was measured in 332 patients by ultra-fast liquid chromatography (UHPLC) and two immunoassays (Liaison Total 25(OH) and ADVIA Centaur Vitamin D Total Assay). Samples from the Vitamin D External Quality Survey (DEQAS) and the Standard Reference Material SRM 972 were used for analytical quality control.


RESULTS
All methods displayed an acceptable performance with DEQAS samples but immunoassays showed a significant bias against certified materials. Compared to UHPLC, differences were significant for both immunoassays in the deficiency interval but the systematic bias was higher for the ADVIA assay throughout the whole range of concentrations.


CONCLUSIONS
The prevalence of vitamin D deficiency in clinical practice is assay-dependent and physicians should be aware of the uncertainty associated with vitamin D assessment.
Servicio de Bioquímica Clínica, Hospital Universitario Puerta de Hierro-Majadahonda, 28222-Madrid, Spain.
Saoud
S
Tahsin-Swafiri
Inmaculada
I
Blanco-Navarro
Belén
B
Pérez-Sacristán
Isabel
I
Millán
Fernando
F
Granado-Lorencio
D002851:Chromatography, High Pressure Liquid; D002853:Chromatography, Liquid / Q000379:methods; D006801:Humans; D007118:Immunoassay / Q000379:methods; D015995:Prevalence; D011786:Quality Control; D012015:Reference Standards; D014807:Vitamin D / Q000097:blood*; D014808:Vitamin D Deficiency / Q000175:diagnosis* / Q000453:epidemiology*
D014807:Vitamin D