Follow-up blood tests after an iron infusion

Have a blood test for ferritin 2 to 3 months after your iron infusion. Above 100, you need no more treatment. Between 50 and 100, a low dose of iron for three months helps your stores settle. Below 50, your stores are running low again and you need more iron. Then retest every 3 to 6 months for two years.

Timing of the test

An infusion is usually a single fixed dose of iron, most often about 1000 mg. The iron does not work overnight. Over the next 4 to 8 weeks it moves into your muscles, skin and other tissues, refills your empty stores and is used to make new red blood cells. Most people notice the benefit by 6 to 8 weeks.

We test at 2 to 3 months, once the iron has settled into your stores, so the result shows how much iron you have left.

Ferritin

Ferritin is the protein that stores iron, and the amount in your blood is the best single measure of how full your stores are. Everyone's normal level is different, anywhere from 50 to 250 micrograms per litre, but as a rule a ferritin above 50 is normal. For some people, such as those with hair loss, we may aim higher, above 100.

Ferritin also rises when the body is fighting an infection or inflammation, so a result taken while you are unwell can look better than it really is. If you have been ill, tell us before the test or wait until you are well.

What your result means

Ferritin above 100: no treatment. Your stores are full. Taking more iron will not help, because a hormone called hepcidin limits how much iron your gut absorbs once your stores are full.

Ferritin 50 to 100: low-dose iron. This may become your normal range. Straight after an infusion, it is worth taking a low dose of iron, 15 to 30 mg a day, for three months to help your level settle. INSERT: Toby to name the low-dose product At this dose iron rarely causes side effects. Retest after three months.

Ferritin below 50: treatment-dose iron. The iron from your infusion has been used up and your stores are running low. The options are a top-up infusion or full-strength iron tablets, with another blood test three months later.

Preparing for the test

Stop any iron tablets 3 to 5 days before your blood test. Ask for ferritin and a full blood count, which includes your haemoglobin. Your GP can usually arrange the test. INSERT: how patients send results to the clinic

Monitoring over two years

People respond to iron infusions in different ways, so we recommend a blood test every 3 to 6 months for two years. You are looking for your ferritin to settle in your own range over time, for example 75, then 64, then 82, then 71. A level that keeps falling points to ongoing blood loss or a problem absorbing iron, which needs looking into.

Ongoing blood loss

If you are still losing blood, for example through heavy periods, the first infusion usually corrects the iron deficiency and the anaemia. Depending on how low your stores were to begin with, a second infusion may be needed to fill them up. In most people, that lasts 3 to 5 years. Treating the cause of the bleeding matters as much as replacing the iron.

Frequently asked questions

Why is my ferritin lower than straight after the infusion? That is expected. Your body has been using the iron to make red blood cells and rebuild its stores, so the level falls and then settles.

Do I need another infusion? Possibly, if your ferritin falls below 50. The options then are a top-up infusion or full-strength tablets, and we will advise which suits you. Most people only need one infusion.

Can I keep taking iron tablets just in case? Not when your ferritin is above 100. Your gut will absorb very little, and tablets can cause side effects for no benefit.

If your result is below 50, or you are not sure what it means, book a consultation with The Iron Clinic.

Sources

1. The Iron Clinic. Follow-up blood results following an iron infusion: clinic guidance. INSERT: date or version
2. The Iron Clinic. Patient information for iron infusion, version 1.5, 7 January 2025. theironclinic.com.
3. Snook J, et al. British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults. Gut 2021;70(11):2030-2051. doi:10.1136/gutjnl-2021-325210
4. NHS. Iron deficiency anaemia. nhs.uk, page last reviewed 26 January 2024, read 13 October 2026.