Abstract
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. Eleven of the 12 participating laboratories performed Ferritin quantitation using automated assay platforms and one laboratory used a manual ELISA kit. 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. 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 10.5µg/ampoule and expanded uncertainty limits 10.2-10.8µg/ampoule (95% confidence; k=2.23).
Highlights
Ferritin is the main storage protein for iron in tissues and is engaged in its uptake, accumulation and release in cells
The results of the international collaborative study to replace the 3rd International Standards (IS) for Ferritin are presented in this article
Seven of the 12 laboratories use the 3rd IS for Ferritin (Human, Recombinant) to calibrate their test kits directly or indirectly, with the remaining five laboratories claiming traceability to either the 1st or 2nd IS for Ferritin
Summary
Ferritin is the main storage protein for iron in tissues and is engaged in its uptake, accumulation and release in cells. The Ferritin molecule is a heterogenous (made up varying proportions of H and L subunits) intracellular hollow protein shell composed of 24 subunits surrounding an iron core that may contain as many as 4,000–4,500 iron atoms. The regulation of Ferritin iron storage has recently been reviewed by Arosio et al [1]. Circulating Ferritin is normally predominantly in the L subunit form and is not iron-bearing. See Worwood [3, 4] and World Health Organization (WHO) [5] for reviews of serum Ferritin. The WHO have recently revised their global guidelines for the use of Ferritin thresholds in patient groups with iron deficiency and those at risk of iron overload [6]
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