Stéphanie Peeters

Evaluation of automated immunoassays for 25(OH)-vitamin D determination in different critical populations before and after standardization of the assays

INTRODUCTION Standardization of immunoassays for 25(OH)-vitamin D determination is a major problem in clinical practice. A worldwide standardization program has started to address this and will reduce the bias observed between immunoassays. We aimed to calibrate 5 immunoassays on a LC-MS/MS traceable to the SRM 2972 and the ID-LC-MS/MS 25(OH)D Reference Method Procedure to see if the re-standardization would be efficient in a population of 3rd trimester pregnant women (PW), hemodialysis (HD) and osteoporosis (OP) patient. MATERIAL AND METHODS 184 serum samples (25(OH)D: 8.4-87 ng/ml) were selected to calibrate the immunoassays (Abbott-Architect, Roche-Elecsys, DiaSorin-Liaison, Siemens-Centaur and IDS-iSYS). Chromsystems MassChrom method was used as the referenced. Serum obtained in 34 PW, 25 HD and 34 OP patients were used as comparatives. RESULTS After adjusting to LC-MS/MS, immunoassays had regression slopes nearly identical to 1.0 with intercepts <0.5 ng/ml. However, in special populations, a systematic bias was still observed, except for iSYS. CONCLUSIONS Re-standardization of 25(OH)D immunoassay will globally improve the differences. However, patients with a different serum matrix will still present significantly different results when they will be run with different methods. For those patients, the LC-MS/MS method seems to be the method of choice, even if some immunoassays are less influenced than others.

Evaluation of the cross-reactivity of 25-hydroxyvitamin D2 on seven commercial immunoassays on native samples

Introduction: In serum, 25-hydroxy-vitamin D (25(OH)D) can be found in two forms, namely 25(OH)D2 and 25(OH)D3. We recently published a mathematical method to estimate the 25(OH)D2 recovery without spiking the samples. Since then, new “total” vitamin D immunoassays have appeared on the market (Roche “Total” vitamin D, Siemens Centaur vitamin D “total”, “total” vitamin D on DiaSorin Liaison XL, Abbott Architect Vitamin D). We aimed to study the 25(OH)D2 recovery of these new immunoassays and re-evaluate the cross-reactivity of previously studied assays (IDS iSYS Vitamin D and DiaSorin RIA).

Analytical and clinical evaluation of the new Fujirebio Lumipulse G non-competitive assay for 25(OH)-vitamin D and three immunoassays for 25(OH)D in healthy subjects, osteoporotic patients, third trimester pregnant women, healthy African subjects, hemodialyzed and intensive care patients

Abstract Background: In this study, we provide a short analytical evaluation of the new Fujirebio Lumipulse®G non-competitive immunoassay for 25(OH)D. Clinical performance was compared with three commercial competitive automated immunoassays against a Vitamin D Standardization Program (VDSP)-traceable liquid chromatography-tandem mass spectrometry (LC-MS/MS) in six different clinically relevant populations. Methods: Lumipulse®G 25(OH)D precision, measurement uncertainty, recovery, limit of quantification were assessed, as well as 25(OH)D2 and C3-epimer recovery. For method comparison, 250 serum 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 the LC-MS/MS. Results: The Lumipulse®G 25(OH)D assay presented interesting analytical features and showed excellent correlation to the LC-MS/MS results (y=1.00×–1.35 ng/mL), as obtained in healthy Caucasian individuals. In the other special populations, Lumipulse®G presented a concordance with LC-MS/MS which was generally higher than competitors, even if all methods significantly under-recovered 25(OH)D in hemodialyzed patients. Intra-assay CV ranged from 12.1% at 9.6 ng/mL to 2.1% at 103.7 ng/mL and inter-assay CV ranged from 16.2 to 3.7% at the same concentrations, respectively. Measurement uncertainty, with a probability of 95%, were respectively 33.1 and 7.6% at these concentrations. LOQ was found to be at 4.6 ng/mL. Mean (95% CI) 25(OH)D2 revovery was 77% (74–81) and no cross-reactivity was observed with C3-epimer. Conclusions: Fujirebio Lumipulse®G 25-OH Vitamin D Total assay is therefore considered suitable for assessment of vitamin D status in clinical routine.

A fast and simple method for simultaneous measurements of 25(OH)D, 24,25(OH)2D and the Vitamin D Metabolite Ratio (VMR) in serum samples by LC-MS/MS (powerpoint)

BACKGROUND Rapid, easy and reliable measurement of the major vitamin D metabolites is required in order to fulfill the needs of a clinical routine laboratory. To overcome these challenges, we have developed and validated a LC-MS/MS method for the quantification of 25-hydroxyvitamin D2 and D3, epi-25-hydroxyvitamin D3 and 24,25-dihydroxyvitamin D3. METHODS Sample preparation was based on precipitation and centrifugation of 100μL of patient serum, followed by injection into the LC-MS/MS system. Samples from Vitamin D Standardization Program (n=80) and patient samples (n=281) have been compared with a reference LC-MS/MS method. For the analytical validation NIST and Labquality quality control materials were used. RESULTS Mean intra-assay and inter-assay imprecision were <6.0 and 6.4% and mean recoveries were within 95-104%. LOQs were 0.5μg/L for 24,25(OH)2D3, 1.1μg/L for 25(OH)D3 and epi-25(OH)D3 and 1.7μg/L for 25(OH)D2. A 3% bias obtained between the proposed and the reference method satisfies Vitamin D Standardization Program recommendations. CONCLUSIONS We present a rapid, easy, reliable and cost-effective method completely adequate for routine testing, which permits the measurement of the ratio of 24,25-dihydroxyvitamin D to 25-hydroxyvitamin D, Vitamin D Metabolite Ratio (VMR), in serum samples.

A simple LC-MS method for the determination of iohexol and iothalamate in serum, using ioversol as an internal standard.

BACKGROUND Chronic kidney disease (CKD) is diagnosed and explored through the determination of the glomerular filtration rate (GFR). Our goal was to develop a simple LC-MS method for the determination in serum of 2 popular GFR markers, contrast agents iohexol and iothalamate, for routine use and comparison studies between the two markers. A similar contrast agent, ioversol, was used as an internal standard and the method underwent a rigorous validation protocol based on β-expectation tolerance intervals. METHODS We adapted the HPLC-UV method from Cavalier et al. to our LC-MS system. Data treatment for the validation was performed using Multiquant 3.0 (Sciex, Framingham, MA, USA) and e.noval 3.0 software (Arlenda, Liège, Belgium). RESULTS According to the validation results our method will give accurate and reliable results for concentrations ranging from 6.8 to 250μg/ml for iohexol and 6.15μg/ml to 250μg/ml for iothalamate. In our practice these intervals are sufficient to determine both compounds in most patient samples. Samples with higher detected concentrations can always be diluted into range. CONCLUSION With its internal standard and extensive validation, our method is now ready for routine and clinical research use.