Analytical Performance Specifications for 25-Hydroxyvitamin D Examinations.

Currently the 25-hydroxy vitamin D (25(OH)D) concentration is thought to be the best estimate of the vitamin D status of an individual. Unfortunately, its measurement remains complex, despite recent technological advances. We evaluated the biological variation (BV) of 25(OH)D in order to set analytical performance specifications (APS) for measurement uncertainty (MU). Six European laboratories recruited 91 healthy participants. The 25(OH)D concentrations in K3-EDTA plasma were examined weekly for up to 10 weeks in duplicate on a Lumipulse G1200 (Fujirebio, Tokyo, Japan). The linear regression of the mean 25(OH)D concentrations at each blood collection showed that participants were not in a steady state. The dissection of the 10-sample collection into two subsets, namely collections 1-5 and 6-10, did not allow for correction of the lack of homogeneity: estimates of the within-subject BV ranged from 5.8% to 7.1% and the between-subject BV ranged from 25.0% to 39.2%. Methods that would differentiate a difference induced by 25(OH)D supplementation at p < 0.05 should have MU < 13.6%, while at p < 0.01, the MU should be <9.6%. The development of APS using BV assumes a steady state of patients. The findings in this study suggest that patients are not in steady state. Therefore, APS that are based on MU appear to be more appropriate.

Analytical and clinical validation of the new Abbot Architect 25(OH)D assay: fit for purpose?

BACKGROUND: We provide a clinical and analytical evaluation of the reformulated version of the Abbott Architect 25-hydroxyvitamin D assay. We compared this assay with three commercial automated immunoassays and against a VDSP-traceable liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) in six different populations. We also supplemented 40 healthy volunteers with either 600,000 IU of vitamin D2 or 100,000 of vitamin D3 to evaluate the performance of the immunoassays vs. the LC-MS/MS. METHODS: Precision and limit of quantification were assessed, 25(OH)D2 and C3-epimer recovery were calculated. Two hundred and forty samples obtained in healthy Caucasians and Africans, osteoporotic, hemodialyzed and intensive care patients and 3rd trimester pregnant women were analyzed by all methods. Correlation was studied using Passing-Bablok and Bland-Altman analysis. Concordance correlation coefficient (CCC) was calculated to evaluate agreement between immunoassays and LC-MS/MS. We verified if patients were homogeneously classified with the immunoassays when they took vitamin D2 or vitamin D3 after 1, 7 and 28 days. RESULTS: We observed excellent analytical features and showed a very good correlation to the LC-MS/MS results in the overall population. Compared to the other immunoassays, concordance of the new Abbott assay with the LC-MS/MS was at least similar, and often better in diseased populations. Althought the cross-reactivity with 25(OH)D2 was not of 100%, there was no significant difference in the classifications of the patients, either supplemented with D2 or D3 or after 7 or 28 days. CONCLUSIONS: This modified version of the Abbott Architect assay is clearly improved compared to the previous one and presents a better agreement with the LC-MS/MS.

Vitamin D status after a high dose of cholecalciferol in healthy and burn subjects.

BACKGROUND: Burn patients are at risk of vitamin D (VD) deficiency and may benefit from its pleiotropic effects as soon as acute phase. Aim of this observational study was to assess effects of a cholecalciferol (VD3) bolus on VD status in adult burn patients (Group B, GB) after admission, compared to healthy subjects (Group H, GH). METHODS: Both groups received an oral dose of 100,000 IU VD3. Blood samples were collected before (D0) and 7 days (D7) after bolus to measure 250H-D, 1,25(OH)2-D, parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23). Albumin (ALB) and VD binding protein (DBP) were measured and used to calculate free 25OH-D level. Data were expressed as median (min-max) or proportions. RESULTS: A total of 49 subjects were included: 29 in GH and 20 in GB. At D0, prevalence of VD deficiency was higher in GB: 25OH-D was 21.5 (10.1-46.3) ng/ml in GH vs 11 (1.8-31.4) ng/ml in GB. DBP and ALB were lower in GB. At D7, DBP was stable in both groups while ALB decreased in GB. 25OH-D increased by 66.6 (13.5-260.3)% in GH. In GB, changes in 25OH-D extended from -36.7% to 333.3% with a median increase of 33.1%. Similar changes were observed in each group for free 25OH-D. High FGF23 levels were observed in GB. CONCLUSIONS: This study highlighted the differences in VD status and in response to a high dose VD3 in burn patients when compared to healthy patients. Pitfalls in VD status assessment are numerous during acute burn care: 25OH-D measurement needs cautious interpretation and interest of free 25OH-D is still questionable. They should not prevent burn patients to receive VD supplements during acute care. Higher doses than general recommendations should probably be considered.