Determination of fibroblast growth factor 23

This version was published on 1 July 2009

Ann Clin Biochem 2009;46:338-340
© 2009 Association for Clinical Biochemistry


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Short Report

Annemieke C Heijboer1,
Marieke Levitus1,
Marc G Vervloet2,
Paul Lips3,
Piet M ter Wee2,
Hilde M Dijstelbloem1 and
Marinus A Blankenstein1

1 Department of Clinical Chemistry;
2 Department of Nephrology;
3 Department of Endocrinology, VU University Medical Center, Amsterdam, The Netherlands

Corresponding author: Dr Annemieke C Heijboer, Department of Clinical Chemistry, VU University Medical Center, De Boelelaan 1118, 1081 HV Amsterdam, The Netherlands. Email: a.heijboer{at}

Background: Fibroblast growth factor 23 (FGF-23) is a recently discoveredhormone, which plays a key role in phosphate regulation. Toinvestigate whether FGF-23 can be determined reliably, we validatedthe three available FGF-23 assays.

Methods: Currently, two intact FGF-23 assays (Kainos; Immutopics) andone C-terminal FGF-23 assay (Immutopics) are available. We determinedintra- and inter-assay variation, linearity and matrix interferencein these assays. Moreover, we compared assay results from healthysubjects with those of patient groups with expected high FGF-23concentrations.

Results: Intra-assay variation was reasonably good in all three assays.Inter-assay variation and linearity were poor for the intactImmutopics assay but reasonable for both other assays. Immutopicsassays gave best results in ethylenediaminetetraacetic acid(EDTA) plasma, while the Kainos assay showed comparable reproducibilityin EDTA plasma and serum. Although the manual of the Kainosassay states that an automatic washing machine can be used,acceptable results were only found by manual washing. Patientswith kidney disease and patients with hypophosphatemic osteomalaciahad increased C-terminal FGF-23 concentrations compared withhealthy controls.

Conclusion: Two assays of reasonable quality are available for FGF-23, theintact FGF-23 assay (Kainos) provided proper attention is paidto the washing procedure, and the C-terminal assay (Immutopics).

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