Serum iron · TIBC · Transferrin saturation · Ferritin
By The Pawline veterinary teamVeterinary-reviewed by Alastair Greenway, BVM&S MRCVS · 25 July 2026
Iron studies exist to answer one question: is an anaemia caused by true iron deficiency, or by chronic inflammation? Both lower serum iron, but they behave differently — iron deficiency raises the carrying capacity (TIBC) and empties the stores (ferritin), while inflammation lowers capacity and raises stores.
Iron is essential for making haemoglobin, so iron problems show up as anaemia. But serum iron alone is nearly useless as a test — it fluctuates through the day and falls in almost any illness. The panel is what makes it informative, because the components move in different directions depending on the cause:
Serum iron — how much iron is circulating right now.
TIBC (total iron-binding capacity) — how much carrying capacity is available (essentially a measure of transferrin, the iron transport protein).
Transferrin saturation — the percentage of that capacity actually filled.
Ferritin — the body's iron stores.
Iron studies distinguish true iron deficiency from anaemia of chronic disease — the components move in opposite directions in each.
The two patterns that matter
This is the whole point of the panel:
True iron deficiency: serum iron low, TIBC HIGH (the body ramps up transport capacity, hunting for scarce iron), saturation very low, ferritin LOW (stores are genuinely empty). The classic cause in dogs and cats is chronic blood loss — a slow gastrointestinal bleed, heavy flea or hookworm burden — because iron leaves with the blood. It typically produces a microcytic anaemia, so a low MCV is often the first clue.
Anaemia of chronic disease (inflammation): serum iron low, TIBC LOW or normal (capacity is not increased), ferritin HIGH (stores are full but locked away). Inflammation deliberately sequesters iron — an ancient defence to starve invading bacteria of it — so iron is unavailable despite being present.
Distinguishing these matters enormously, because iron supplementation helps the first and does nothing for the second, where the treatment is to address the underlying inflammatory disease.
A ferritin caveat worth knowing
Ferritin is also an acute-phase protein, meaning inflammation raises it independently of iron stores. So a "normal" ferritin in an inflamed patient can mask genuinely depleted stores. This is why ferritin is read alongside the inflammatory markers (CRP in dogs, SAA in cats) rather than taken at face value, and why the full panel beats any single component.
Reading iron overload
High iron and high saturation are uncommon and can reflect over-supplementation, haemolysis releasing iron, liver disease, or (rarely) iron-storage disorders. Iron is not benign in excess, so a genuinely high result is investigated rather than ignored.
In chronic disease
Iron studies are used to characterise an anaemia at the outset and then to monitor the response to treatment — a recovering ferritin and saturation alongside a rising haematocrit and reticulocyte count is the picture of successful iron repletion. In chronic kidney disease, iron status is assessed alongside the reduced red-cell production that characterises that anaemia.
Cat vs dog
The two patterns and their interpretation are the same in both species. Ferritin assays are species-specific and are not routinely available everywhere, so in practice the panel run may be limited to iron, TIBC and saturation. Chronic blood loss from parasites or gastrointestinal bleeding is a leading cause of true iron deficiency in each.
About the reference range
This page shows no range strip. Iron studies comprise several analytes with laboratory- and species-specific intervals (and ferritin assays vary considerably), and Pawline draws a band only where it holds a verified interval. Read each component against the ranges printed on your own report, and interpret them as a pattern rather than individually.
For orientation only, one published example: Cornell University's veterinary laboratory reports serum iron 97–263 µg/dL (≈17–47 µmol/L) in dogs and 59–169 µg/dL (≈11–30 µmol/L) in cats; TIBC 280–489 µg/dL (dog) and 222–423 µg/dL (cat); and transferrin saturation 27–66% (dog) and 20–56% (cat). Ferritin is a send-out, assay-specific test with no universal interval — take its range from the performing laboratory. As always these are one lab's figures; your own report's ranges are what count.
What to do next
If your pet is anaemic — particularly with small red cells (a low MCV) — iron studies are the tests that distinguish true iron deficiency (which needs a source of blood loss found, plus iron replacement) from anaemia of chronic disease (which needs the underlying inflammation treated). Ask for the panel rather than serum iron alone, and expect it to be interpreted alongside inflammatory markers, given ferritin's acute-phase behaviour.
This page is educational and is not a diagnosis. Lab results are interpreted in the full clinical context by your veterinary surgeon; a single value rarely tells the whole story.
