Measurement of Vitamin D metabolites: an international perspective on methodology and clinical interpretation

doi:10.1016/j.jsbmb.2004.03.055

The Journal of Steroid Biochemistry and Molecular Biology

Volumes 89–90, May 2004, Pages 467-471

https://doi.org/10.1016/j.jsbmb.2004.03.055 Get rights and content

Abstract

The International Quality Assessment Scheme for Vitamin D metabolites (DEQAS) was introduced in 1989. Initially, the aim was to improve the reliability of 25-hydroxyvitamin D (25-OHD) assays but the scheme was extended in 1997 to include 1,25-dihydroxyvitamin D (1,25(OH)₂D). DEQAS has 95 members in 18 countries (January 2003). Five serum samples are distributed quarterly and participants are given up to 6 weeks to return their results for statistical analysis. The majority of participants use commercial kits for both analytes. A performance target was set by an advisory panel in 1997 and, at present, requires participants to get 80% or more of their results within ±30% of the All-Laboratory Trimmed Mean (ALTM). The performance targets are under continual review. In 2003, 59% of participants met the target (cf. 52% in 2000). A questionnaire, distributed in January 2003, requested information on methods and the interpretation of results. Reference ranges varied but there was reasonable agreement on the 25-OHD concentrations below which Vitamin D supplementation was advised. A minority (22%) of respondents was unsure whether Vitamin D₃ or Vitamin D₂ was used to treat patients in their locality. The majority (52%) of assays for 1,25(OH)₂D were done ’on demand’ and others for apparently spurious reasons. Most respondents thought participation in DEQAS extremely important and the planned introduction of on-line reporting should enhance its value.

Introduction

The International External Quality Assessment Scheme for Vitamin D metabolites (DEQAS) was established in 1989 following consistent reports of poor performance for assays of 25-hydroxyvitamin D (25-OHD) [1], [2] and 1,25-dihydroxyvitamin D (1,25(OH)₂D) [1]. Initially DEQAS covered only 25-OHD but was extended to include 1,25(OH)₂D in 1997. The number of participants have grown from approximately 25 in 1989 to 95 in 2003, of whom 37 currently also measure 1,25(OH)₂D. The aim of DEQAS was to improve the accuracy and precision of these assays by regularly distributing serum samples to participants throughout the world and thus establishing performance targets. It was initially intended to provide GC–MS values for all samples distributed but this has not been possible. However, the All Laboratory Trimmed Mean (ALTM) [3] was shown to be an appropriate routine target value by comparison with GC–MS [4]. To encourage improved performance, certificates of proficiency are awarded to all participating laboratories whose performance meets the target set by an advisory panel [5]. The initial performance target was set in 1997 and required participants to get 80% or more of their results within ±33% of the ALTM. The target is under continual review, was altered to ±30% in 2000 and is likely to be tightened further over the coming years.

Demand for 25-OHD and 1,25(OH)₂D assays has undoubtedly been stimulated by the introduction of commercial kits, which are designed for ease of use in non specialist laboratories. In common with other routinely measured analytes, the reliability of results can only be assessed by participation in an external quality assessment scheme. Indeed, this is often required as part of the laboratory accreditation process. Rapid feedback and efficient communication between participants and scheme organisers is considered to be extremely important. To facilitate this, a web-based reporting system has been developed [6]; DEQAS participants sending results via the internet will have immediate access to up-dated statistics. The addition of a ‘message board’ will facilitate communication between participants, manufacturers and DEQAS. In addition to monitoring assay performance, DEQAS is in a unique position to collate information about the use and interpretation of 25-OHD and 1,25(OH)₂D assays. To this end, DEQAS distributed a questionnaire to all participants in January 2003. The results of this questionnaire are reported here together with details of performance over the last 3 years.

Section snippets

Serum pools

Blood was collected anonymously from polycythaemic patients undergoing therapeutic venesection. The serum was stored at −40 °C. Prior to distribution, pools were thawed and screened for Hepatitis B and C, and HIV. To ensure sterility, the serum was passed through a 0.2 μm biological grade filter. Pools were stored at 4 °C overnight and dispensed as 0.5 ml (25-OHD) or 2 ml (1,25(OH)₂D) samples for distribution. Samples were sent to participants at ambient temperature by first class post (UK) and by

Performance

Fig. 1 shows the percentage of participants meeting the performance target for each of the last three distribution cycles. During this 3-year period, the number of participants increased by about 33%.

Location of participants and methods

Thirteen different countries were represented in 2000 [5] and since then participants from a further five countries (Finland, Iceland, Lebanon, Luxembourg and The Netherlands) have been added. Fig. 2 shows the methods used by those returning results for the January 2003 distribution.

Reference ranges and intervention criteria

Fifty-five

Discussion

The availability of commercial kits has undoubtedly led to a worldwide increase in the number of 25-OHD and 1,25(OH)₂D assays performed. The apparent simplicity and ease of use of these kits has encouraged the use of these methods in non-specialised laboratories. The need for external as well as internal quality assessment has therefore never been greater. It is perhaps disappointing that in 2003, the fairly undemanding target set by DEQAS has only been achieved by 59% of participants and has

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Hypovitaminosis D in bariatric surgery: A systematic review of observational studies
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Citation Excerpt :
We searched the following databases: Medline, PubMed, the Cochrane Library, and EMBASE. The search timeframe was 2000–April 2015, since the accuracy of vitamin D assays has improved in the last decade, following the introduction of the International Quality Assessment Scheme for Vitamin D metabolites (DEQAS), in 1997 [48]. We used the following MeSH terms: vitamin D, vitamin D deficiency, bariatrics, bariatric surgery, gastric bypass, gastroplasty, biliopancreatic diversion, anastomosis, Roux-en-Y, gastroenterostomy, pancreaticojejunostomy, gastrectomy, jejunoileal bypass, obesity, overweight.
Obesity is a public health problem that carries global and substantial social and economic burden. Relative to non-surgical interventions, bariatric surgery has the most substantial and lasting impact on weight loss. However, it leads to a number of nutritional deficiencies requiring long term supplementation.
The aims of this paper are to review 25-hydroxyvitamin D [25(OH)D] status pre and post bariatric surgery, describe the dose response of vitamin D supplementation, and assess the effect of the surgical procedure on 25(OH)D level following supplementation.
We searched Medline, PubMed, the Cochrane Library and EMBASE, for relevant observational studies published in English, from 2000 to April 2015. The identified references were reviewed, in duplicate and independently, by two reviewers.
We identified 51 eligible observational studies assessing 25(OH)D status pre and/or post bariatric surgery. Mean pre-surgery 25(OH)D level was below 30 ng/ml in 29 studies, and 17 of these studies showed mean 25(OH)D levels ≤ 20 ng/ml. Mean 25(OH)D levels remained below 30 ng/ml following bariatric surgery, despite various vitamin D replacement regimens, with only few exceptions. The increase in post-operative 25(OH)D levels tended to parallel increments in vitamin D supplementation dose but varied widely across studies. An increase in 25(OH)D level by 9–13 ng/ml was achieved when vitamin D deficiency was corrected using vitamin D replacement doses of 1100–7100 IU/day, in addition to the usual maintenance equivalent daily dose of 400–2000 IU (total equivalent daily dose 1500–9100 IU). There was no difference in mean 25(OH)D level following supplementation between malabsorptive/combination procedures and restrictive procedures.
Hypovitaminosisis D persists in obese patients undergoing bariatric surgery, despite various vitamin D supplementation regimens. Further research is needed to determine the optimal vitamin D dose to reach desirable 25(OH)D levels in this population, and to demonstrate whether this dose varies according to the surgical procedure.
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Results: After standardization (cycles 1 and 2 combined), the percentage of Canadians with 25(OH)D values <40 nmol/L increased from 16.4% (original) to 19.4% (standardized), and values <50 nmol/L increased from 29.0% (original) to 36.8% (standardized). The 25(OH)D standardized distributions (cycles 1 and 2 analyzed separately) were similar across age and sex groups; slightly higher values were associated with cycle 2 in the young and old. This finding contrasts with the original data, which indicated that cycle 2 values were lower for all age groups.
Conclusion: The shifts in 25(OH)D distribution brought about by standardization indicate its importance in drawing correct conclusions about potential population deficiencies and insufficiencies and in permitting the comparison of distributions between national surveys.
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Results: At 8 wk postpartum, mean [nmol/L (95% CI)] infant 25(OH)D at 8 wk was higher in the 50-μg/d [75 (67, 83)] than in the 25-μg/d [52 (45, 58)] or 10-μg/d [45 (38, 52)] vitamin D groups (P < 0.05). Fewer infants born to mothers in the 50-μg/d group had a 25(OH)D concentration <30 nmol/L (indicative of deficiency) than infants in the 25- and 10-μg/d groups, respectively (2% compared with 16% and 43%; P < 0.05). Fewer than 15% of infants in the 10- or 25-μg/d groups achieved a 25(OH)D concentration >75 nmol/L compared with 44% in the 50-μg/d group (P < 0.05). Almost all infants (~98%, n = 44) born to mothers in the 50-μg/d group achieved a 25(OH)D concentration >30 nmol/L. At 8 wk postpartum, mean maternal 25(OH)D concentration was higher in the 50-μg/d [88 (84, 91)] than in the 25-μg/d [78 (74, 81)] or 10-μg/d [69 (66, 73)] groups (P < 0.05).
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The maximal calcium absorption in response to vitamin D has been proposed as a biomarker for vitamin D sufficiency.
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This was a placebo-controlled, dose-response, randomized, double-blind study of the effect of vitamin D on calcium absorption in healthy postmenopausal women. Seventy-six healthy postmenopausal women were randomly assigned to placebo or 800 IU (20 μg), 2000 IU (50 μg), or 4000 IU (100 μg) vitamin D₃ for 8 wk. The technique of dual isotopes of stable calcium was used with a calcium carrier to measure calcium absorption at baseline and after 8 wk.
Seventy-one women with a mean ± SD age of 58.8 ± 4.9 y completed the study. The mean calcium intake was 1142 ± 509 mg/d and serum 25(OH)D was 63 ± 14 nmol/L at baseline. A statistically significant linear trend of an increase in calcium absorption adjusted for age and body mass index with increasing vitamin D₃ dose or serum 25(OH)D concentration was observed. A 6.7% absolute increase in calcium absorption was found in the highest vitamin D₃ group (100 μg). No evidence of nonlinearity was observed in the dose-response curve.
No evidence of a threshold of calcium absorption was found with a serum 25(OH)D range from 40 to 130 nmol/L. Calcium absorption in this range is not a useful biomarker to determine nutritional recommendations for vitamin D. This trial was registered at clinicaltrials.gov as NCT01119378.

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^☆: Presented at the 12th Workshop on Vitamin D (Maastricht, The Netherlands, 6–10 July 2003).

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Measurement of Vitamin D metabolites: an international perspective on methodology and clinical interpretation☆

Abstract

Introduction

Section snippets

Serum pools

Performance

Location of participants and methods

Reference ranges and intervention criteria

Discussion

An international comparison of vitamin D metabolite measurements

Clin. Chem.

Inter-laboratory comparison of 25-hydroxyvitamin D determination

Clin. Chem.

Outliers in clinical chemistry quality control schemes

Clin. Chem.