The iron panel, line by line: seven numbers that only read together

Storage: ferritin, the panel's main line

Ferritin is the storage protein of iron, and its blood level reflects the size of the body's reserves. Guidelines for iron-deficiency anemia rely on ferritin as the key criterion of deficiency: stores run out long before hemoglobin falls, so low ferritin with normal hemoglobin is latent, hidden deficiency.

Ferritin has a trap: it is an acute-phase protein, and any inflammation — from a cold to a flare of chronic disease — raises it regardless of real stores. Ferritin is therefore never read without inflammatory context: with high CRP, a normal ferritin does not exclude deficiency.

Transport: iron, transferrin and TIBC

Serum iron is the most unstable line: it swings through the day, reacts to food and to iron supplements, so a single value says little. Transport capacity is shown by transferrin, the carrier protein, while total iron-binding capacity (TIBC) reflects the total number of free seats on it.

In iron deficiency the liver ramps up transferrin synthesis: transferrin and TIBC rise while iron falls. In chronic inflammation the picture is mirrored: transferrin drops and TIBC falls together with iron. These two situations — deficiency and inflammation — are told apart precisely by the transport lines.

The calculated line: transferrin saturation

Transferrin saturation is the ratio of serum iron to TIBC, in per cent: how many seats on the carrier are actually occupied. It is a steadier guide than iron itself because it accounts for both transport lines at once. Low saturation with high transferrin is the classic signature of iron deficiency.

High saturation, in contrast, raises the question of iron overload: hereditary hemochromatosis or excessive intake. In that branch ferritin is high too, but without the inflammatory caveat — a completely different story with its own route.

Marrow demand: soluble transferrin receptors

Soluble transferrin receptors (sTfR) are fragments of the receptors cells display when they run short of iron. The stronger the cellular hunger, the more receptors appear in blood. The marker's main virtue is that it barely reacts to inflammation, unlike ferritin, so it helps separate true deficiency from the functional iron block of chronic disease.

In practice sTfR acts as a second instance: when ferritin is middling, CRP is high and the question 'is there deficiency' stays open. The ratio of sTfR to log ferritin is a calculated index used in difficult mixed anemias.

The regulator: hepcidin, the gate valve of iron

Hepcidin is a liver hormone, the master regulator of the whole system: it closes the exit of iron from storage cells and from the gut into the blood. In inflammation hepcidin rises and locks iron inside cells — hence the functional deficiency of chronic disease: the body has enough iron, but it is unavailable for blood formation.

In true deficiency hepcidin is suppressed instead: the body opens every gate for absorption. The marker remains a second-tier test so far — it is used in difficult cases where the standard lines contradict each other, such as anemia of chronic disease with suspected deficiency on top.

Three typical combinations in an iron panel

Markers covered in this article

Frequently asked questions

Sources

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