The association of circulating ferritin with serum concentrations of fibroblast growth factor-23 measured by three commercial assays

Ann Clin Biochem 2007;44:463-466
© 2007 Association for Clinical Biochemistry


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Original Articles

Brian H Durham,
Frank Joseph,
Lisa M Bailey and
William D Fraser

Department of Diabetes and Endocrinology, Royal Liverpool University Hospital, Liverpool, UK;
Department of Clinical Biochemistry and Metabolic Medicine, Royal Liverpool University Hospital, Liverpool, UK

Background: The measurement of the serum concentration of fibroblastgrowth factor-23 (FGF-23) is beginning to be used as a diagnostictool in renal phosphate wasting disorders. Having observed anincreased serum FGF-23 in three subjects with low circulatingferritin concentrations we investigated the association betweenlow ferritin and raised serum FGF-23.

Methods: We measured FGF-23 in 150 random anonymized serum samples with ferritin concentrations between <5 and 50 µg/Lusing three commercially available enzyme-linked immunosorbentassay (ELISA) kits. One kit, Human FGF-23[C-term] (ImmutopicsInc, USA) measures total FGF-23 whereas the other two kits,Immutopics intact and FGF-23 ELISA (Kainos, Japan) are reportedto measure only the biologically active intact molecule.

Results: We have detected a significant inverse correlation of -0.565 (P<0.0001) between serum ferritin when <50 µg/Land FGF-23 using the C-terminal assay. This relationship isalso shown with the Immutopics intact assay but is not demonstratedwith the Kainos intact assay.

Conclusion: The measurement of FGF-23 by both Immutopics assaysis altered in the presence of low circulating concentrationsof serum ferritin whereas with the Kainos intact assay thiseffect was not demonstrated. Serum ferritin should be measuredwhen an elevated FGF-23 is obtained using the Immutopics C-terminalor intact FGF-23 assay to prevent misdiagnosis of the causeof this abnormality.

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