Ferritin thresholds by setting
Australian Prescriber describes a low ferritin as the most reliable initial marker of iron deficiency without anaemia. A ferritin below 30 ug/L has a sensitivity of 92 per cent and a specificity of 98 per cent for iron deficiency, and corresponds to the absence of iron stores in the bone marrow.
Ferritin is also an acute phase protein. It rises with inflammation, independently of how much iron is stored. So in any condition that carries inflammation, a higher ferritin can still mean depleted stores, and guidance raises the cut-off to compensate.
| Setting | Iron deficiency is suggested by | Source |
|---|---|---|
| General population | Ferritin below 30 ug/L | Balendran 2021 |
| Inflammation present | Ferritin below 100 ug/L with transferrin saturation below 20 per cent | Balendran 2021 |
| Pregnancy | Ferritin below 30 ug/L | Clarke 2025 |
| Before surgery | Ferritin below 30 ug/L, or below 100 ug/L with CRP above 5 mg/L and/or transferrin saturation below 20 per cent | Muñoz 2017 |
| Heart failure | Ferritin below 100 ug/L, or below 300 ug/L with transferrin saturation below 20 per cent | ESC, via Balendran 2021 |
| Chronic kidney disease | Ferritin below 500 ug/L with transferrin saturation below 30 per cent | KDIGO, via Balendran 2021 |
A ferritin of 250 ug/L can count as iron deficiency in someone with heart failure and a low transferrin saturation. A ferritin of 25 ug/L counts as iron deficiency in a healthy woman. Neither number, by itself, tells you whether an infusion is the right treatment.
Trial entry thresholds
Clinical trials choose entry thresholds to suit their question. Our IRONWOMAN trial, for example, enrolled recreationally active women with ferritin below 20 ug/L and haemoglobin above 115 g/L. That was an entry criterion for a study population. Athlete research uses a higher cut-off still, covered in what ferritin level a female athlete should have.
Indications for an infusion
Australian Prescriber is clear that for uncomplicated iron deficiency, oral iron is readily available, effective, safe, convenient and cost effective. It lists the main indications for intravenous iron as:
- Oral iron that has not worked, through failure, poor adherence or intolerance
- Malabsorption, for example coeliac disease or bariatric surgery
- Inflammatory bowel disease
- Chronic kidney disease treated with erythropoiesis-stimulating drugs
- A need to raise iron quickly, such as before urgent surgery or after acute blood loss
- Heart failure
None of these is a ferritin value.
Going straight to an infusion
A second Australian Prescriber article notes that intravenous iron is usually only indicated after oral iron has failed, but that some groups may benefit without a trial of tablets: people with heart failure with reduced ejection fraction, people on haemodialysis, and pregnant women in the second or third trimester who need iron replaced quickly.
Two consensus statements add time as the deciding factor.
The international consensus statement on surgery recommends intravenous iron as front-line treatment when oral iron has not worked or cannot be tolerated, or when surgery is planned less than six weeks after iron deficiency is diagnosed. For people who are not anaemic but face surgery with a high risk of severe anaemia afterwards, it suggests oral iron, with intravenous iron considered if surgery is less than four weeks away or tablets cannot be tolerated.
The 2025 Australian consensus statement on pregnancy, which I contributed to, recommends oral iron first, and offering intravenous iron to women who are intolerant of or not responding to oral iron, or who are in the third trimester.
Tablets work for most people given long enough. An infusion earns its place when tablets cannot be absorbed, cannot be tolerated, have already failed, or there is not enough time left for them to work.
Ferritin level and urgency
Partly. A lower ferritin means less iron in reserve. The surgical consensus statement notes that in a healthy adult the serum ferritin level reflects stored iron, and that a patient with a low ferritin may not have enough iron in reserve to recover from the blood lost at an operation. The less there is, the more there is to rebuild, and Australian researchers note that replenishing iron stores with oral iron can take considerable time. That strengthens the case for speed when time is short.
But lower iron status also raises the risk of one of the main side effects of intravenous iron. A 2021 meta-analysis of 42 trials found low blood phosphate in 47 per cent of patients after ferric carboxymaltose and 4 per cent after iron isomaltoside, and identified low baseline ferritin and low transferrin saturation as risk factors. So the people with the most depleted stores are also the people most likely to develop low phosphate after the most commonly used product, which made up 93.9 per cent of intravenous iron dispensed to Australian women aged 18 to 44 in 2024.
That risk is a reason to ask which product is being proposed, and why. The wider reasons a general practitioner (GP) may hold back are set out in why your doctor may be reluctant to give you an iron infusion.
Testing conditions
A threshold is only as good as the test it is applied to. Australian Prescriber gives practical detail on testing:
- The ideal sample is a fasting morning sample, taken after oral iron has been withheld for at least 24 hours. After a course of tablets, repeat iron studies about one week after stopping.
- Because ferritin rises with inflammation, guidance pairs it with transferrin saturation when inflammation may be present, and the surgical consensus statement uses a C-reactive protein (CRP) above 5 mg/L as the marker of inflammation.
- Iron studies are repeated approximately 60 to 90 days after intravenous iron, or as clinically appropriate.
Variation between prescribers
Two women with similar results can reasonably be told different things. A 2026 analysis of Pharmaceutical Benefits Scheme data found more than threefold variation in intravenous iron dispensing to Australian women aged 18 to 44 between states and territories, with the highest rate consistently in Western Australia. Earlier growth in use has been put down mainly to an unrestricted Pharmaceutical Benefits Scheme (PBS) listing of ferric carboxymaltose, and the authors suggest the variation may reflect differences in clinical indication or local practice guidelines.
How a result is acted on can depend partly on where you live and who you see.
Questions for your doctor
- Am I iron deficient on the threshold that fits my situation? If inflammation or a chronic condition is involved, ask whether a higher ferritin cut-off and transferrin saturation apply.
- Was the sample taken fasting, in the morning, with oral iron withheld?
- Have I had a fair trial of oral iron? If not, and there is no reason to skip it, tablets are the guideline first step. This piece on tablets that are not working covers what a fair trial looks like.
- Is there a reason for speed, such as upcoming surgery, late pregnancy, or ongoing losses that tablets cannot keep up with?
- Do we know what caused the deficiency, and how it will be treated?
- If an infusion is appropriate, which product, and how does its risk of low phosphate compare with the alternatives?
Related articles
- Iron infusions and doctor reluctance
- Ferritin and fatigue
- A Practical Guide to Iron Deficiency and Anaemia
Sources
The figures and thresholds on this page come from these papers.
- Balendran S, Forsyth C. Non-anaemic iron deficiency. Australian Prescriber 2021;44(6):193-196. doi:10.18773/austprescr.2021.052
- Canning M, Grannell L. A stain on iron therapy. Australian Prescriber 2020;43(5):160-163. doi:10.18773/austprescr.2020.051
- Clarke L, Froessler B, Tang C, et al. Iron optimisation in pregnancy: a Haematology in Obstetric and Women's Health Collaborative consensus statement. Internal Medicine Journal 2025;55(2):300-307. doi:10.1111/imj.16602
- Muñoz M, Acheson AG, Auerbach M, et al. International consensus statement on the peri-operative management of anaemia and iron deficiency. Anaesthesia 2017;72(2):233-247. doi:10.1111/anae.13773
- Schaefer B, Tobiasch M, Viveiros A, et al. Hypophosphataemia after treatment of iron deficiency with intravenous ferric carboxymaltose or iron isomaltoside: a systematic review and meta-analysis. British Journal of Clinical Pharmacology 2021;87(5):2256-2273. doi:10.1111/bcp.14643
- Kassie GM, Jackson H, Clarke L, et al. Increasing utilisation of intravenous iron among Australian women of reproductive age, 2013-2024: an Australian population-based study. Internal Medicine Journal 2026;56(9):1536-1543. doi:10.1111/imj.70494
- Dugan C, Peeling P, Buissink P, et al. Effect of intravenous iron therapy on exercise performance, fatigue scores and mood states in iron-deficient recreationally active females of reproductive age: a double-blind, randomised control trial (IRONWOMAN Trial). British Journal of Sports Medicine 2025;59(13):921-930. doi:10.1136/bjsports-2024-108240
This article is educational and not medical advice. Thresholds and treatment decisions should always be interpreted by a qualified clinician who knows your full history.