Extracellular iron concentrations are mainly controlled by hepcidin, an iron-regulatory hormone. Hepcidin mediates iron influx into the plasma from tissues involved in iron storage and transport, and is physiologically increased by elevated plasma iron concentration and inflammation. Although hepcidin is an important marker for iron homeostasis and iron-related pathologies, reliable methodologies for measuring hepcidin concentrations have been limited. However, a competitive enzyme-linked immunoassay (C-ELISA) for human hepcidin has recently been developed. This assay gives clinicians a highly improved means of detecting physiological and pathological changes in both serum and urine hepcidin levels.

To develop the assay, a highly selective antibody to human hepcidin was purified, and the resulting fitted curves of the assay were used to convert absorbance readings to hepcidin concentrations. Serum samples from healthy volunteers were then obtained to confirm the selectivity, precision, reproducibility, and stability of the assay. The serum from these volunteers was also used to establish a normal range of hepcidin (29-254 ng/mL in men and 17-286 ng/mL in women).

After establishing positive correlations with urine hepcidin and ferritin levels, plasma hepcidin concentrations were measured by C-ELISA after iron loading to examine physiologic responses. Subjects with detectable iron absorption experienced a corresponding, but more prolonged rise in serum hepcidin. Furthermore, C-ELISA measurements for hepcidin were taken in subjects with various iron disorders. In tests focusing on patients with hemochromatosis, iron-overload showed inappropriately normal levels of serum hepcidin, while iron-depletion showed low levels. Patients with inflammation, multiple myeloma, and chronic kidney disease also showed abnormal increases in serum hepcidin.

From the test results, the C-ELISA for human hepcidin has proven to be a very useful clinical tool for detecting physiologic and pathologic variations in hepcidin concentrations. Not only does the assay reliably detect expected physiological conditions, but it also provides a means of better understanding the pathology of various iron disorders. For example, hepcidin concentrations could be useful as diagnostic measurements, and may be informative about disease etiology. The authors conclude that large-scale human studies will be needed to elucidate further clinical applications.

Ganz T, Olbina G, Girelli D, Nemeth E, Westerman M. Immunoassay for human serum hepcidin. Blood. 2008 Aug 8.

NAAC Expert Commentary:
Although initially described as an antimicrobial peptide, the essential role of hepcidin as a regulator of iron homeostasis was ultimately described. Hepcidin regulates iron absorption and transport through ferroprotein. Quantification of hepcidin levels has advanced our understanding of normal and pathologic conditions of iron metabolism.

In this study, Ganz and colleagues reported on a competitive ELISA to quantify serum hepcidin levels. They first demonstrated that serum hepcidin by this assay correlates well with the more onerous urine assay used by these investigators. Hepcidin levels correlated closely with serum ferritin in normal healthy adults (r = 0.63) as the body responds to reduced iron stores by suppression of hepcidin and enhancement of iron absorption. The normal serum ranges of hepcidin levels were described in healthy adults. As expected, the median values were lower in women because of lower iron stores on average.

In various disorders of iron metabolism, hepcidin levels varied as demonstrated by other studies. For example, in iron deficiency, hepcidin levels were highly suppressed, whereas during inflammatory states, hepcidin levels were elevated. Elevated hepcidin from inflammation has been implicated in anemia of inflammation by reducing functional iron availability. Finally, hepcidin levels were also shown to be inappropriately normal in hereditary iron overload.

Measuring hepcidin is critical to understanding normal and perturbed iron metabolism. However, the currently available assays have major limitations that preclude clinical use. The serum immunoassay reported by Ganz and colleagues holds promise to translate quickly into a commercially available test. The results are in line with prior studies of hepcidin and validate the utility of hepcidin in several disorders. For now, serum ferritin and iron indices will remain the first-line tests to gauge iron stores. However, serum hepcidin may augment studies of iron stores by shedding light on iron metabolism. For example, elevated hepcidin may support a diagnosis of anemia of chronic inflammation and a functional iron deficiency that may respond to iron supplementation. Before measures of hepcidin have clinical utility, validation studies will clearly be needed to determine diagnostic thresholds.

Last Modified: October 1, 2008