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.

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

Anaemia is a major global health problem. Although the main cause is iron deficiency, anaemia also results from other nutritional deficiencies (folate and vitamin B12), haemolytic disorders including haemoglobinopathies, and bone marrow disorders. Accurate diagnosis of anaemia is dependent on reliable diagnostic tests and reference ranges, which in turn are dependent on effective standardisation. Standardisation is achieved through the availability of reference materials and reference measurement procedures. International biological reference materials have therefore been developed to standardise and control diagnostic tests for anaemia for a diverse range of analytes including total haemoglobin and haemoglobin types, ferritin, the serum transferrin receptor, serum vitamin B12 and folate, whole blood folate, and alloantibodies which mediate immune haemolytic anaemia.

Preliminary evaluation of the performance of a new, highly sensitive commercial immunoassay for serum ferritin determination.

We evaluated the analytical performance of a new, commercial, fully automated immunoturbidimetric assay for the determination of ferritin [FER-Latex(X2)CN SEIKEN, Denka Seiken, Japan] in serum on the Olympus AU2700 analyzer. The new assay is a latex-enhanced turbidimetric immunoassay with an analysis time of 10 min. The linearity of the assay was confirmed up to 2505 pmol/L (R2=0.999). The detection limit and the functional sensitivity were both 4.5 pmol/L. The intra- and inter-assay imprecision (CV) at 67, 506, 2186 pmol/L was < 1.8% and < 2.5%, respectively. Verification of the traceability to a WHO standard (80/578) showed a recovery of 102.6% (target value 449 pmol/L). No hook effect was observed in samples containing up to 33,705 pmol/L. The assay showed good correlation with the Beckman Immage nephelometric system (r=0.999). Hemoglobin (< or = 9.8 g/L), total bilirubin (< or = 113 micromol/L), conjugated bilirubin (< or = 109 micromol/L) and rheumatoid factor (< or = 5.2x10(5) IU/L) did not interfere with the assay. The reference interval (2.5-97.5 percentile) was 72-521 pmol/L for men and 27-267 pmol/L for women. The reference interval in patients with anemia, malignant tumors and hemochromatosis was 5.6-52, 130-2436 and 1465-2903 pmol/L, respectively. On the basis of the receiver operating characteristic curve, the 90% sensitivity cut-off value to distinguish between patients with and without iron deficiency was 40 pmol/L. The new latex turbidimetric procedure for ferritin assay is an attractive alternative that avoids the need for dedicated instrumentation.

International collaborative study to evaluate a recombinant L ferritin preparation as an International Standard.

A recombinant L ferritin preparation, lyophilized in ampoules and designated 94/572, was evaluated by 18 laboratories in 9 countries for its suitability as an International Standard (IS). The preparation was assayed in a wide range of in-house and commercial immunoassays against the 2nd IS for ferritin (of spleen origin; 80/578). The immunological reactivity of the recombinant material was similar to that of the 2nd IS for ferritin in the majority of assays and demonstrated adequate stability in accelerated degradation studies. On the basis of the results presented here, the WHO Expert Committee on Biological Standardization established 94/572 as the 3rd IS for ferritin, recombinant.

Calibration of Abbott AxSYM Ferritin kit using the WHO Human Liver Ferritin International Standard 80/602.

A commercial ferritin kit (Abbott AxSYM Ferritin) was calibrated using the WHO Human Liver Ferritin International Standard 80/602. The reconstituted WHO freeze-dried standard was diluted to obtain six concentration levels ranging from 10-840 micrograms/l. In the analysis of the data, logarithmic transformation of the results was performed in order to stabilize the variance. The AxSYM kit yielded slightly higher values than the WHO Ferritin Standard (p < 0.05). The relation between the AxSYM kit and the WHO Ferritin Standard (untransformed values) was described by a proportionality: FerritinAxSYM = 1.057 x FerritinWHO. WHO Ferritin Standard values of 12 and 15 micrograms/l (used as cut-off values for absent or small body iron reserves) yielded calculated AxSYM values of 12.7 and 15.9 micrograms/l. A WHO Ferritin Standard value of 30 micrograms/l (used threshold value for the presence of stainable bone marrow haemosiderin iron) yielded a calculated AxSYM value of 31.7 micrograms/l.

Determination of serum ferritin by a one-step immunoenzymoassay, and comparison of four liver-ferritin standards.

We describe a one step "sandwich"-type immunoenzymoassay for ferritin in human serum. The solid-phase consists of glutaraldehyde-treated polypropylene tubes coated with rabbit antibody to human ferritin. Liver ferritin is the standard. Peroxidase-conjugated antiserum to ferritin and a sensitive chromogen, o-phenylenediamine, are used. The assay requires 90 min. The standard curve is linear up to 400 micrograms of ferritin per liter of serum. Within- and between-run CVs are less than 6% for low, high, and medium concentrations and are about 13.0% at the decision level for iron deficiency. Results by a two-step "sandwich" procedure (New England Immunology Associates kit) correlated well, r = 0.98. We assessed four liver ferritin standards from different manufacturers with the described method. The mean absorbance for the 40 micrograms/L ferritin standard was 1.5 for that from Diagnostics Biochem and National Institute for Biological Standards and Controls, 1.0 for that from Dako, and 0.4 for that from Sigma. Consequently, to standardize results, all liver ferritin standards should be calibrated vs the National Institute for Biological Standards and Controls reference standard.

A determination of thickness and surface relief in reembedded sections of an epoxy- and a melamine-resin containing ferritin as size standard.

Chemical and physical data of two electron microscopic embedding media (the non-polar epoxy resin Epon 812 and the polar melamine resin Nanoplast FB 101) suggest that less kinetic energy must be applied for cutting a section from a Nanoplast block than from an Epon block of the same hardness and that, consequently, the cutting qualities of Nanoplast are better. To test this hypothesis, normal and extremely thin sections of Epon- and Nanoplast-embedded horse spleen ferritin micropellets were reembedded and resectioned for a determination of thickness and surface roughness. The ease with which extremely thin sections can be cut from the Nanoplast resin (8 nm versus 15 nm in Epon) and the smooth surface of these sections support the hypothesis that the cutting quality of an embedding material is determined primarily by its energy balance, i.e. by the kinetic energy which must be introduced for sectioning and the bonding energy which is released exothermically from a polymer while being sectioned.

Use of a reference standard to improve the accuracy and precision of seven kits for determination of ferritin in serum.

We assessed the accuracy and precision of seven commercial kits for serum ferritin. The concentration of ferritin as determined by these assays for a liver ferritin reference standard, a human heart ferritin standard, and normal sera correlated highly, but the absolute values varied widely. Use of an international reference standard for ferritin to prepare the standard curve greatly diminished the variability, but did not eliminate it. Although the seven kits differed in specificity for various human isoferritins, this did not appear substantially to affect accuracy. Six of the seven kits appeared sufficiently precise for clinical use over a wide range of ferritin concentrations.

A single site serum ferritin immunoradiometric assay. A comparison between serum and liver ferritin standards and two antibody preparations.

A single site immunoradiometric assay (1S-IRMA) for serum ferritin was developed to investigate some standardization problems in the assay of ferritin. In comparison to this 1S-IRMA, a 2-site solid phase IRMA gave lower answers of serum ferritin in the normal reference range, as well as in serum from idiopathic hemochromatosis patients. Purified serum ferritin or liver ferritin gave different standard curves in this new immunoassay system and the differences obtained were further dependent on the antibody preparation employed. The different isoferritin profiles obtained, dependent on the antibody preparation employed for ferritin purification, indicate a different antibody specificity for different ferritin subunits. Serum ferritin purified from different serum pools from healthy persons showed similar isoferritin profiles and immunoassay reactivities.