What a full iron panel includes

An iron panel blood test usually combines four measurements: serum iron, transferrin or total iron-binding capacity (TIBC), transferrin saturation and ferritin. Ferritin describes your stored iron; the other three describe what is circulating right now and how full the transport system is.

Ferritin is the body’s iron reserve, like a strongbox put away for later. A reserve and a flow answer different questions, which is why a report that gives only serum iron is hard to interpret.

  1. FerritinThe reserve, and the line that matters most for the common question: are you short of iron?
  2. Serum ironWhat is circulating at the moment of the draw, which is why iron tests are usually done in the morning.
  3. TIBC or transferrinHow much capacity the blood has to carry iron, measured through the protein that does the carrying.
  4. Transferrin saturationThe percentage of that capacity actually filled; below 20% is a widely used sign of shortage.

Iron panel vs ferritin, and is iron in a CBC?

A complete blood count does not measure iron. It shows hemoglobin and the size of the red cells, which change only once a shortage has lasted long enough to affect red cell production. Ferritin alone answers the reserve question; a full iron panel adds the circulating side.

That gap is larger than most people expect. In US national survey data on females aged 12 to 21, 38.6% were iron deficient by ferritin, yet among those with iron deficiency, 83.6% did not have anemia: their blood count looked normal while their reserve was low. A normal CBC does not rule out low iron.

The ferritin cutoff is genuinely disputed

This is the part worth knowing before you compare your figure with anything. US reports print ferritin in ng/mL, which is the same number as the µg/L used in many studies, so 30 ng/mL and 30 µg/L are identical.

A systematic review of 29 guidelines from professional associations found that recommendations for diagnosing iron deficiency vary widely, and concluded that a ferritin cutoff of 100 should be considered in most conditions, with transferrin saturation at 20%, except in particular situations such as young healthy women with heavy periods. A Swiss expert consensus, working on people without inflammation, found that 30 gives good accuracy for iron deficiency without anemia, and that 30 to 50 with a saturation below 20% can also indicate it. In the United States, the American Gastroenterological Association recommends a cutoff of 45 rather than 15 when ferritin is used to diagnose iron deficiency in people with anemia.

Read together, the practical conclusion is clear: a ferritin of 25 with a laboratory floor of 15 is not automatically fine, and the lower limit printed on your report is one convention among several. This is a question for your doctor with your symptoms in hand, not a line to settle from a table.

30
Swiss consensus cutoff, without inflammation (ng/mL)[4]
45
US gastroenterology cutoff in anemia (ng/mL)[5]
100
Cutoff suggested in most conditions by a review of 29 guidelines (ng/mL)[3]

Inflammation can hide a deficiency

Ferritin is also an acute-phase protein: it rises with inflammation, independently of how much iron you have stored. Inflammatory bowel disease, heart failure, chronic kidney disease or a passing infection can therefore lift ferritin into the normal range while the reserve underneath is low.

This is why an iron panel is read next to an inflammation marker such as CRP, and why transferrin saturation is useful. In those chronic conditions, a review of the evidence treats a ferritin below 100, or a saturation below 20%, as consistent with iron deficiency, and a ferritin of 100 to 300 with a saturation below 20% as confirming it.

The reverse case is simpler: inflammation pushes ferritin up, not down, so a low ferritin is hard to explain away.

Low iron, low ferritin, or high: what each suggests

Low iron or low ferritin: which is worse? They are not rivals but different measurements. Every guideline in the 29-guideline review defined iron deficiency with ferritin, because it reflects the reserve. A low serum iron on its own describes a single moment, and inflammation can hold it down even when stores are adequate.

High values have their own short list. A raised serum iron can point toward iron overload such as hemochromatosis, toward lead poisoning or toward liver disease, while a high ferritin often reflects inflammation rather than too much iron. Which explanation applies is read from the whole panel, so a high value is a reason for a conversation with your doctor rather than a conclusion.

Before the test, and after it

Your provider may ask you to fast for 12 hours, and iron tests are usually done in the morning. If you take an iron supplement, tell the laboratory and ask whether to pause it beforehand, since the answer depends on which lines are being measured.

And if a deficiency is found, the question of why matters more than the number. Iron deficiency is a finding that asks for an explanation, to the point that US gastroenterologists have published a guideline on how to look for its cause in people with anemia. The explanation is what the consultation is for.