Optimizing hepcidin measurement with a proficiency test framework and standardization improvement

Objectives: Hepcidin measurement advances insights in
pathophysiology, diagnosis, and treatment of iron disor-
ders, but requires analytically sound and standardized
measurement procedures (MPs). Recent development of a
two-level secondary reference material (sRM) for hepcidin
assays allows worldwide standardization. However, no
proficiency testing (PT) schemes to ensure external quality
assurance (EQA) exist and the absence of a high calibrator
in the sRM set precludes optimal standardization.
Methods: We developed a pilot PT together with the
Dutch EQA organization Stichting Kwaliteitsbewaking Medische Laboratoriumdiagnostiek (SKML) that included 16 international hepcidin MPs. The design included 12 human serum samples that allowed us to evaluate accu- racy, linearity, precision and standardization potential. We manufactured, value-assigned, and validated a high-level calibrator in a similar manner to the existing low- and middle-level sRM.Results: The pilot PT confirmed logistical feasibility of an annual scheme. Most MPs demonstrated linearity (R2>0.99) and precision (duplicate CV>12.2%), although the need for EQA was shown by large variability in accuracy. The high- level calibrator proved effective, reducing the inter-assay CV from 42.0% (unstandardized) to 14.0%, compared to 17.6% with the two-leveled set. The calibrator passed in- ternational homogeneity criteria and was assigned a value of 9.07 ± 0.24 nmol/L.Conclusions: We established a framework for future PT to enable laboratory accreditation, which is essential to ensure quality of hepcidin measurement and its use in patient care. Additionally, we showed optimized standardization is possible by extending the current sRM with a third high calibrator, although international implementation of the sRM is a prerequisite for its success.