Iron status is assessed from a venous blood sample: a ferritin test plus an iron panel and a complete blood count, run by a laboratory — no home device measures it. The markers are routine and cheap, and one requisition covers them. The reading is awkward because no single value settles the question: iron depletion moves through stages, and each marker turns at a different one. Our entry on Iron deficiency says what the condition is; this page is about getting your own numbers.
What you need
One blood draw, ideally in the morning. Ask for:
- Ferritin — the stored-iron marker, and the most informative single value here.
- Serum iron and total iron-binding capacity (TIBC), or transferrin. Together they give transferrin saturation, the share of carrying capacity loaded with iron.
- A complete blood count: hemoglobin, MCV, MCH and RDW.
- C-reactive protein, in the same draw. Without it a ferritin result cannot be read safely.
Serum iron swings through the day and jumps for hours after an iron tablet, so laboratories generally want a morning, fasting sample with supplements paused beforehand — ask yours how long. If you have no results yet and are weighing whether the draw is worth arranging, a symptom screen such as Hidden iron deficiency answers a softer question: whether your tiredness, hair loss and cold hands warrant testing. It does not replace the panel.
How the measurement works
Iron leaves the body in stages, and the panel reads that sequence. Stores go first: ferritin falls while everything else looks normal, the stage called iron deficiency without anemia. Transport goes next: serum iron drops, the liver makes more transferrin so TIBC climbs, and Transferrin saturation (TSAT) — serum iron divided by TIBC — falls. Only then does red cell production suffer, so MCV, MCH and finally hemoglobin decline. A low hemoglobin means the deficiency has been running a while.
Reading that by hand means holding six values, three units and one ratio at once, and lower limits differ between assays. That arithmetic is what Iron deficiency assessment is for: enter ferritin, hemoglobin, MCV, transferrin saturation and TIBC in the units your report prints, and it places you on the sequence rather than judging each line separately.
How to read the result
Read the pattern across markers, not one flagged line:
| Marker | What it reflects | In iron deficiency |
|---|---|---|
| Ferritin | Stored iron | Falls first, and furthest |
| Transferrin saturation | Iron in transit | Falls once stores are empty |
| TIBC / transferrin | Spare carrying capacity | Rises as stores empty |
| RDW | Spread of red cell sizes | Rises early |
| MCV and MCH | Red cell size and hemoglobin content | Fall late |
| Hemoglobin | Oxygen-carrying capacity | Falls last, and that is anemia |
The usual anchors are conventions, not constants. The World Health Organization treats ferritin below roughly 15 micrograms per liter in adults as depleted stores, though many clinicians act on a higher figure, since the low one misses people already symptomatic; transferrin saturation under about 20 percent signals that supply is limiting production; and the anemia threshold for hemoglobin differs for men and women. Read against the range your own report prints.
What it does not tell you
It does not tell you why. Low iron is a finding, not a diagnosis: heavy menstrual bleeding, slow blood loss from the gut, celiac disease, gastric surgery, a low-iron diet or poor absorption all produce the same numbers. Unexplained iron deficiency in an adult is a reason to look for a source of bleeding, and that search is a clinician’s job.
Ferritin is an acute-phase protein, its central weakness. Infection, chronic inflammation, liver disease, heavy alcohol use and obesity all raise it, so a normal-looking ferritin can sit on top of empty stores. That is why C-reactive protein (CRP) belongs in the same draw, and why higher ferritin thresholds apply when inflammation is present; transferrin saturation then carries more weight.
Nor does it identify every anemia. Small red cells with normal stores point elsewhere — thalassemia trait, for instance — B12 or folate deficiency produces large cells, and anemia of chronic disease can mimic iron deficiency yet is managed differently. Treatment is outside the panel too: oral or intravenous iron, the dose, and when to retest depend on the cause, not on the numbers alone.
Related reading
Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.