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Read ferritin first: in adults, ferritin below 30 µg/L means iron deficiency. Then check transferrin saturation: below 20% means little iron is available to make red blood cells. Ferritin rises with inflammation, so a normal ferritin can hide a deficiency when CRP is raised. Read iron studies alongside CRP and the full blood count.
What’s in an iron study
- Ferritin: the best single measure of stored iron
- Serum iron: the iron circulating at the time of collection. It moves around too much to read on its own
- Transferrin and TIBC: the blood’s capacity to carry iron, which rises when stores run low
- Transferrin saturation: how much of that carrying capacity is in use
Reading ferritin
The RCPA recommends 30 µg/L as the lower limit for ferritin in adults, and a result below it indicates iron deficiency. Some services, such as Australian Red Cross Lifeblood, use 15 µg/L for women, but women with ferritin between 15 and 30 µg/L may also be iron deficient.
It’s common. In Australia, 22.3% of women and 3.5% of men have ferritin below 30 µg/L.
When inflammation changes the picture
Ferritin rises with inflammation, obesity, fatty liver disease and other chronic conditions, so it can look normal while stores are low. In someone with an inflammatory condition, ferritin below 70 µg/L may still point to iron deficiency.
Inflammation can also cause functional iron deficiency, where there are stores but the body can’t release them. Ferritin is normal or high while transferrin saturation is low. That’s why CRP belongs next to every iron study.
Transferrin saturation
Transferrin saturation below 20% means little iron is available, from either low stores or iron that’s locked away by inflammation. A high saturation with a high ferritin is a different picture that can point to iron overload, and needs medical follow-up.
Common patterns
| Pattern | Ferritin | Transferrin saturation | Full blood count |
|---|---|---|---|
| Iron replete | 30 µg/L or more | Above 20% | Normal |
| Iron deficiency | Below 30 µg/L | Below 20% | Normal early, then anaemia with low MCV and MCH |
| Functional iron deficiency | Normal or raised, often with inflammation | Below 20% | Mild to moderate anaemia possible |
| Both together | Below about 70–100 µg/L, depending on the inflammation | Below 20% | Mild to moderate anaemia possible |
Adapted from Zhang et al., MJA 2024. Reference intervals vary by laboratory; use the ranges on your client’s report.
The full blood count
Haemoglobin tells you whether there’s anaemia. A low MCV and MCH are sensitive signs of iron deficiency anaemia when B12 and folate are normal. Low stores often show up in ferritin before haemoglobin falls.
When to involve the GP
New iron deficiency in an adult needs a cause, not only a supplement. Blood loss is the most common cause, mostly from the gut. Guidelines recommend coeliac serology, and investigation of the gut is routinely considered for adults with iron deficiency. Refer back to the GP for new iron deficiency, any anaemia, a high ferritin you can’t explain, or a high transferrin saturation.
Iron studies in Vively
The Baseline Health Check includes iron studies (ferritin, iron, transferrin, TIBC and transferrin saturation), a full blood count and hs-CRP from one blood draw. Each result shows the laboratory range, with a Vively optimal range beside it where the evidence supports one. Vively also calculates a ferritin-to-CRP ratio to help you read ferritin in context.
Sources
- Zhang GD, Johnstone D, Leahy MF, Olynyk JK. Updating the diagnosis and management of iron deficiency in the era of routine ferritin testing of blood donors by Australian Red Cross Lifeblood. Med J Aust 2024;221(7):360
- RCPA: Iron Studies Standardised Reporting Protocol, 2nd edition (2021)
- RCPA Manual: Iron studies
