Does HFE C282Y (rs1800562) heterozygosity raise serum iron and transferrin saturation while leaving ferritin normal?

Clinical and phenotypic evidence

Large-scale population studies and genome-wide association studies (GWAS) demonstrate that individuals who are heterozygous for the HFE C282Y mutation (rs1800562) have significantly higher circulating iron parameters compared to those with wild-type alleles.

• Serum iron and transferrin saturation (TSAT): Heterozygous carriers typically exhibit elevated serum iron concentrations and a corresponding increase in TSAT. While these levels often remain within or near the upper limit of the physiological reference range, they are statistically and clinically higher on average than in non-carriers.
• Ferritin mismatch: In contrast to the clear elevations in circulating iron, the effect of C282Y heterozygosity on serum ferritin—the primary marker of long-term cellular iron storage—is minimal and highly variable. Most heterozygotes maintain completely normal ferritin levels, and clinical iron overload is rare.
• Clinical impression: This biological divergence means that a patient's circulating iron indices (TSAT and serum iron) can present as highly replete or elevated, creating the impression of high iron status, even though actual cellular iron storage (ferritin) remains entirely normal or even low.

Mechanistic explanations

The distinct biochemical profile of C282Y heterozygotes is driven by specific alterations in iron transport and regulation:

• HFE-Hepcidin axis: The HFE gene encodes a membrane protein that regulates the iron-sensing complex and controls the expression of hepcidin, the master iron-regulatory hormone. A single C282Y mutant allele slightly impairs this pathway, leading to mild, relative hepcidin deficiency. This permits increased dietary iron absorption and greater iron release into the bloodstream.
• Reduced transferrin levels: Genetic data demonstrate that the C282Y allele is associated with lower circulating levels of transferrin (the primary iron-binding transport protein in the blood). Because TSAT is calculated as the ratio of serum iron to total iron-binding capacity (which is directly determined by transferrin levels), the combination of higher serum iron and lower transferrin concentrations mathematically compounds and drives up the TSAT percentage.

Bottom line

Heterozygosity for the HFE C282Y mutation typically causes an elevation in serum iron and transferrin saturation while leaving the storage marker ferritin relatively unaffected. Clinicians and patients should be aware of this genetic mismatch, as circulating iron markers may falsely suggest systemic iron overload when tissue iron stores are actually within the normal range.