Ferritin 20: iron tablets or an iron infusion?

Ferritin 20 µg/L can indicate depleted iron stores, but the result alone does not determine whether tablets or an iron infusion are needed. The choice depends on haemoglobin, the cause of the deficiency, iron absorption and tolerance of treatment. Oral iron is usually the starting point in standard situations; intravenous iron needs a specific clinical reason.

“My ferritin is 20. Do I need iron tablets, or is it time for an infusion?” This is a common question after a blood test. Intravenous treatment does not automatically become preferable because someone wants to replenish their stores quickly. First, it is necessary to establish whether iron deficiency is present, whether there is anaemia and why the deficiency developed.

Does ferritin 20 mean iron deficiency or anaemia?

Iron deficiency and iron deficiency anaemia are different conditions. Ferritin reflects stored iron: the lower the concentration, the more likely the stores are depleted. Haemoglobin can remain normal despite low iron stores.

• Normal haemoglobin with low ferritin can be consistent with iron deficiency without anaemia.
• Low haemoglobin together with confirmed iron deficiency can indicate iron deficiency anaemia.

Ferritin is also an acute-phase protein. Inflammation can raise its concentration and conceal an iron deficiency. When inflammation is present, ferritin alone may therefore be insufficient; a clinician may also assess C-reactive protein, or CRP, and transferrin saturation, or TSAT.

A ferritin result around 20 µg/L can be consistent with iron deficiency, especially alongside other laboratory findings and symptoms. The treatment route, however, is selected from the overall clinical picture rather than a single number.

When are iron tablets usually the first choice?

Oral iron is usually the first option for confirmed iron deficiency when there is no reason to expect poor absorption or an inadequate treatment response. This approach is described in the British Society of Gastroenterology guidance.

Intravenous iron is considered when oral treatment is not tolerated, is ineffective or is contraindicated. If a person can take the medicine, tolerates it and is expected to absorb it normally, oral treatment is usually a reasonable first step. Ferritin 20 alone is not an indication for an iron infusion.

Why is an infusion not always preferable?

Intravenous iron replenishes stores more quickly, but speed does not establish a clinical need. For most patients with iron deficiency anaemia, the eventual haematological response to oral and intravenous iron is comparable.

An iron infusion is a medical procedure with its own potential risks. Some intravenous preparations can cause hypophosphataemia, meaning a low blood phosphate level. The risk varies with the preparation and administration schedule. Wanting the ferritin result to rise faster is therefore not, on its own, enough reason to choose this route.

When is intravenous iron appropriate?

Intravenous treatment can be appropriate when oral iron is unsuitable, does not work or cannot compensate for the deficiency quickly enough. A clinician considers several situations.

Oral treatment is not tolerated. Significant nausea, abdominal pain, constipation or other adverse effects can interfere with treatment. Before switching routes, it may be reasonable to discuss taking a smaller amount at each administration, using an alternate-day schedule or trying a different oral preparation. Changes should be agreed with the clinician rather than made independently.

Iron is poorly absorbed. Certain bowel conditions or operations on the stomach or small intestine may reduce iron absorption. Intravenous treatment can sometimes be preferable from the outset in these circumstances.

Significant blood loss is continuing. Oral treatment may not keep up when the body is losing large amounts of iron. Intravenous iron may replenish the deficit more quickly, while the cause of the loss also needs attention.

Rapid correction is clinically important. In selected situations, such as marked anaemia or preparation for surgery, timing matters. The clinician may choose intravenous treatment earlier than in a standard situation.

Oral treatment has not produced a response. If a person is taking the medicine but laboratory results do not improve, the reason should first be investigated. When appropriately managed oral therapy remains ineffective, intravenous treatment becomes a more reasonable option. The American Gastroenterological Association also identifies intolerance, lack of improvement and expected poor absorption as reasons to use intravenous iron.

What if haemoglobin is normal?

Iron deficiency without anaemia needs a separate assessment. The approach used for marked iron deficiency anaemia should not automatically be applied to it. For example, haemoglobin of 135 g/L and ferritin of 20 µg/L can represent normal haemoglobin alongside reduced iron stores.

The clinician considers symptoms, diet, menstrual losses and other possible sources of bleeding, inflammatory disease, iron studies and other health conditions. Iron treatment can be reasonable for symptomatic deficiency without anaemia, but the evidence for routine management is less clear than it is for iron deficiency anaemia.

The decision should therefore be individual. Ferritin 20 with normal haemoglobin does not automatically mean that intravenous iron is needed.

How can you tell whether treatment is working?

In anaemia, treatment should produce a measurable haematological response. Checking ferritin again after only a few days is not enough to assess success. BSG recommends monitoring haemoglobin in the early weeks. A rise of approximately 10 g/L within two weeks in an anaemic patient taking daily oral iron is a good sign of response; the review schedule depends on the treatment regimen.

If the expected response is absent, the clinician checks possible explanations before changing the route:

• An insufficient amount of iron being taken or difficulty following the agreed schedule.
• Continuing blood loss.
• Poor absorption.
• Inflammation or another illness.
• Coexisting vitamin B12 or folate deficiency.

A lack of improvement is a reason to investigate, rather than automatically conclude that tablets do not work. Follow-up blood tests help assess the result and decide whether the treatment plan needs to change.

How is the choice between tablets and an infusion made?

The route is chosen after assessing the deficiency, any anaemia and the likelihood of responding to oral treatment. When there is no marked anaemia, malabsorption or significant ongoing blood loss, tablets are tolerated and a full course is feasible, there is usually no need to start with intravenous iron.

Useful questions for a consultation include whether iron deficiency is confirmed, whether anaemia is present, why the stores fell, whether absorption is expected to be adequate and whether rapid replacement is clinically necessary. Tablets are the initial option in most standard situations. Intravenous treatment is used when there is a specific reason for it.

For a broader review of blood tests and symptoms, discuss the appropriate assessment with a clinician; the Longevity Day page describes a comprehensive assessment approach. For another possible contributor to persistent tiredness, read about thyroid function and chronic fatigue.

Author: Dr. Daria Filipovich — Nutritionist-Gastroenterologist · Clinical Nutrition.