The development and role of international biological reference materials in the diagnosis of anaemia

Paediatric reference intervals and curves for haemoglobin and ferritin: protocol for a systematic review and meta-analysis

INTRODUCTION

Reference intervals and reference curves provide clinicians with a point of reference when evaluating patients' laboratory test results. In practical applications, the 2.5th and 97.5th percentiles of healthy reference population are typically used as lower and upper reference limits. Guidelines outlining analytical and methodological steps involved in reference intervals and curves estimation are available and there have been large-scale world-wide initiatives to provide reference intervals and curves for children. However, there is a lack of synthesised evidence regarding the results of such initiatives in general, but specifically in iron-related biomarkers, ferritin (in serum and plasma) and haemoglobin. Objectives of this review are to identify studies that have produced reference intervals and curves for ferritin and haemoglobin in paediatric populations and to synthesise all available evidence. We also aim to quantify heterogeneity across reference intervals and curves and identify and elucidate sources of heterogeneity, including heterogeneity in the methods employed in their development.

METHODS AND ANALYSIS

Using a comprehensive search strategy, we will identify eligible studies. Following electronic databases will be searched from inception: EMBASE, MEDLINE, SCOPUS and The Cochrane Library. We will also perform grey literature search to capture unpublished reference intervals and curves from healthy cohorts. Two researchers will independently screen retrieved citations against eligibility criteria in two stages, focusing first on titles and abstracts and then on full-text articles. Studies that provide reference intervals and curves for ferritin and haemoglobin for paediatric population will be eligible. Data extraction will include study characteristics, characteristics of reference population, methodological and analytical considerations and estimated reference intervals and curves. We will consider narrative synthesis and quantitative synthesis when appropriate.

ETHICS AND DISSEMINATION

Ethical approval is not required as data from already published studies will be used. Results will be disseminated through peer-reviewed publications and conference presentations.

PROSPERO REGISTRATION NUMBER

CRD42023399802.

Harmonization Status of Serum Ferritin Measurements and Implications for Use as Marker of Iron-Related Disorders

BACKGROUND

Serum ferritin is considered a suitable biomarker of iron-related disorders. However, data about the comparability of results among commercial measuring systems (MSs) are contradictory. We performed an intercomparison study aimed at verifying the current interassay variability and its impact on clinical application of the test. Obtaining this information is vital because manufacturers continue to claim calibration alignment to different WHO preparations, which are not related to each other in terms of traceability.

METHODS

Four widely used MSs were evaluated. The interassay agreement was verified using 39 human serum pools. The recovery of WHO International Standard (IS) 94/572 (the only reference material available at the time of the study) was evaluated, after assessing the material commutability. Finally, an approach for harmonizing ferritin results was proposed.

RESULTS

Highly significant differences (P < 0.00001) among ferritin concentrations assayed by different MSs were detected and the interassay CV (median 22.9%; interquartile range 21.8-25.5) overlapped the desirable intermethod bias (24.6%). IS 94/572 was commutable for use only with Access and Centaur, with Access being the only MS correctly recovering its assigned value. Accordingly, we used regression data against Access to recalibrate MSs, indirectly aligning them to IS 94/572, with a substantial improvement in degree of harmonization and traceability to higher-order reference.

CONCLUSIONS

The harmonization among evaluated ferritin MSs is far from optimal, with the implementation of traceability to different WHO ISs being a factor of confusion. A recalibration approach, however, would permit measurement harmonization, allowing the use of common decision thresholds.

International collaborative study to evaluate and calibrate two recombinant L chain Ferritin preparations for use as a WHO International Standard

OBJECTIVES

To evaluate and calibrate two candidate preparations for the 4th International Standard for Ferritin (Human, Recombinant) (codes: 19/118 and 19/162) against the 3rd International Standard for Ferritin (Human, Recombinant) (code: 94/572), and three serum commutability samples in an international collaborative study involving 12 laboratories in nine countries.

METHODS

Eleven of the 12 participating laboratories performed Ferritin quantitation using automated assay platforms and one laboratory used a manual ELISA kit.

RESULTS

There was better overall agreement between all laboratories and between assay methods for the potency of preparation 19/118 than for preparation 19/162. The overall geometric mean potency (from all methods) of the candidate 4th International Standard, 19/118, was 10.5 µg/ampoule, with inter-laboratory variability, expressed as % geometric coefficient of variation (GCV), of 4.7%. Accelerated stability studies have predicted both 19/118 and 19/162 to be very stable for long term storage at -20 °C.

CONCLUSIONS

The candidate 4th International Standard for Ferritin (Human, Recombinant) (19/118) has been shown to be immunologically similar to the 3rd International Standard for Ferritin (Human, Recombinant) (94/572). It was recommended to and accepted by the WHO Expert Committee on Biological Standardization that 19/118 be established as the 4th International Standard for Ferritin (Human, Recombinant) with an assigned potency of 10.5 µg/ampoule and expanded uncertainty limits 10.2-10.8 µg/ampoule (95% confidence; k=2.23).

Biomarkers of Nutrition for Development (BOND)-Iron Review

This is the fifth in the series of reviews developed as part of the Biomarkers of Nutrition for Development (BOND) program. The BOND Iron Expert Panel (I-EP) reviewed the extant knowledge regarding iron biology, public health implications, and the relative usefulness of currently available biomarkers of iron status from deficiency to overload. Approaches to assessing intake, including bioavailability, are also covered. The report also covers technical and laboratory considerations for the use of available biomarkers of iron status, and concludes with a description of research priorities along with a brief discussion of new biomarkers with potential for use across the spectrum of activities related to the study of iron in human health.The I-EP concluded that current iron biomarkers are reliable for accurately assessing many aspects of iron nutrition. However, a clear distinction is made between the relative strengths of biomarkers to assess hematological consequences of iron deficiency versus other putative functional outcomes, particularly the relationship between maternal and fetal iron status during pregnancy, birth outcomes, and infant cognitive, motor and emotional development. The I-EP also highlighted the importance of considering the confounding effects of inflammation and infection on the interpretation of iron biomarker results, as well as the impact of life stage. Finally, alternative approaches to the evaluation of the risk for nutritional iron overload at the population level are presented, because the currently designated upper limits for the biomarker generally employed (serum ferritin) may not differentiate between true iron overload and the effects of subclinical inflammation.

Performance and comparability of laboratory methods for measuring ferritin concentrations in human serum or plasma: A systematic review and meta-analysis

BACKGROUND

Different laboratory methods are used to quantify ferritin concentrations as a marker of iron status. A systematic review was undertaken to assess the accuracy and comparability of the most used methods for ferritin detection.

METHODS AND FINDINGS

National and regional databases were searched for prospective, retrospective, sectional, longitudinal and case-control studies containing the characteristics and performance of at least one method for serum/plasma ferritin determinations in humans published to date. The analysis included the comparison between at least 2 methods detailing: sensitivity, precision, accuracy, predictive values, inter-methods adjustment, and use of international reference materials. Pooled method performance was analyzed for each method and across methods.

OUTCOMES

Search strategy identified 11893 records. After de-duplication and screening 252 studies were assessed, including 187 studies in the qualitative analysis and 148 in the meta-analysis. The most used methods included radiometric, nonradiometric and agglutination assays. The overall within-run imprecision for the most reported ferritin methods was 6.2±3.4% (CI 5.69-6.70%; n = 171), between-run imprecision 8.9±8.7% (CI 7.44-10.35%; n = 136), and recovery rate 95.6% (CI 91.5-99.7%; n = 94). The pooled regression coefficient was 0.985 among all methods analyzed, and 0.984 when comparing nonradiometric and radiometric methods, without statistical differences in ferritin concentration ranging from 2.3 to 1454 μμg/L.

CONCLUSION

The laboratory methods most used to determine ferritin concentrations have comparable accuracy and performance. Registered in PROSPERO CRD42016036222.

Laboratory methodologies for indicators of iron status: strengths, limitations, and analytical challenges

Biochemical assessment of iron status relies on serum-based indicators, such as serum ferritin (SF), transferrin saturation, and soluble transferrin receptor (sTfR), as well as erythrocyte protoporphyrin. These indicators present challenges for clinical practice and national nutrition surveys, and often iron status interpretation is based on the combination of several indicators. The diagnosis of iron deficiency (ID) through SF concentration, the most commonly used indicator, is complicated by concomitant inflammation. sTfR concentration is an indicator of functional ID that is not an acute-phase reactant, but challenges in its interpretation arise because of the lack of assay standardization, common reference ranges, and common cutoffs. It is unclear which indicators are best suited to assess excess iron status. The value of hepcidin, non-transferrin-bound iron, and reticulocyte indexes is being explored in research settings. Serum-based indicators are generally measured on fully automated clinical analyzers available in most hospitals. Although international reference materials have been available for years, the standardization of immunoassays is complicated by the heterogeneity of antibodies used and the absence of physicochemical reference methods to establish "true" concentrations. From 1988 to 2006, the assessment of iron status in NHANES was based on the multi-indicator ferritin model. However, the model did not indicate the severity of ID and produced categorical estimates. More recently, iron status assessment in NHANES has used the total body iron stores (TBI) model, in which the log ratio of sTfR to SF is assessed. Together, sTfR and SF concentrations cover the full range of iron status. The TBI model better predicts the absence of bone marrow iron than SF concentration alone, and TBI can be analyzed as a continuous variable. Additional consideration of methodologies, interpretation of indicators, and analytic standardization is important for further improvements in iron status assessment.

Tracing a roadmap for vitamin B₁₂ testing using the health technology assessment approach

In our hospital, we are currently working to manage the appropriateness of vitamin B₁₂ (B12) testing. Unfortunately, the classic evidence-based approach is unhelpful in this process and meta-analyzing data on the accuracy of this marker for cobalamin deficiency detection is misleading due to the lack of reference diagnostic methods. The approach currently proposed by the Health Technology Assessment (HTA) enables us to tackle the issue of B₁₂ requests as a "healthcare" problem by considering the position of stakeholders involved in ordering, performing, interpreting the test, and receiving its results. Clinical expectations, methodological issues, and ethical aspects concerning the performance of the test can aid us in providing more guidance on the use of this marker. By building such structured information, hemodialysis patients and pregnant women have emerged as those groups preferentially requiring B₁₂ testing, as it may potentially improve the clinical outcome. To avoid misinterpretation of B₁₂ results more care should be taken in considering its biochemical and biological features, as well as the analytical issues. Spurious values obtained by current automated immunoassays may reflect suboptimal pre-analytical steps as well as known interfering conditions. Furthermore, the harmonization of results by available methods is still a far-reaching goal and the approach to interpret an individual's results should be improved. Tracing a roadmap for B₁₂ testing by exploiting the HTA model to balance the stakeholders' claims and maximizing the patient's outcome may help to manage the marker demand.

Diagnosis of anaemia: old things rearranged

Anaemia is one of the most leading causes of morbidity and mortality, as declared by the World Health Organisation. This syndrome is characterised by low haemoglobin levels and nonspecific clinical symptoms such as weakness, fatigue and dyspnoea. The symptoms are unspecific as the underlying causes are heterogeneous. Thus, good knowledge of the useful biomarkers and their correct assignment is needed to allow rapid and targeted diagnosis.

Soluble transferrin receptor (sTfR) and sTfR/log ferritin index for the diagnosis of iron-deficiency anemia. A meta-analysis

Determination of serum soluble transferrin receptor (sTfR) is proposed to distinguish between iron-deficiency anemia and anemia of chronic disease. Here we conducted a meta-analysis of the literature to evaluate the diagnostic efficacy of sTfR and sTfR/log ferritin index. The meta-analysis included 18 sTfR and 10 sTfR index studies. Three sTfR index studies were, however, eliminated as outliers. The odds ratio was significant for both sTfR (22.9, 95% confidence interval [CI], 9.6-55.0) and sTfR index (9.5, 95% CI, 5.0-18.1) in a heterogeneous set of studies. Meta-analysis for sensitivity, specificity, and likelihood ratios (LRs) was performed only in a subset of 10 sTfR studies. The overall sensitivity, specificity, and positive and negative LRs were 86%, 75%, 3.85, and 0.19, respectively, with an area under summary receiver operating characteristic curve of 0.912 (standard error, 0.039). Additional studies are needed to define the overall diagnostic accuracy of sTfR.

Advances in standardization of laboratory measurement procedures: implications for measuring biomarkers of folate and vitamin B-12 status in NHANES

Population studies such as NHANES analyze large numbers of laboratory measurements and are often performed in different laboratories using different measurement procedures and over an extended period of time. Correct clinical and epidemiologic interpretations of the results depend on the accuracy of those measurements. Unfortunately, considerable variability has been observed among assays for folate, vitamin B-12, and related biomarkers. In the past few decades, the science of metrology has advanced considerably, with the development of improved primary reference measurement procedures and high-level reference materials, which can serve as the basis for accurate measurement. A rigorous approach has been established for making field methods traceable to the highest-level reference measurement procedures and reference materials. This article reviews some basic principles of metrology and describes their recent application to measurements of folate and vitamin B-12.