Ferritin and haemoglobin: A dietitian's guide

Sophie Mumby, Registered Dietitian (HCPC)

Iron-related blood tests are among the most common ones I see clients bring to appointments, and they're often misunderstood. Here's a simple guide to hopefully help you understand your readings better.

Haemoglobin (Hb) is the oxygen-carrying protein in red blood cells. A low level indicates anaemia, which has many possible causes, including iron deficiency, low B12 or folate, chronic disease and blood loss.

Ferritin reflects your body's iron stores. Low ferritin means your stores are depleted, even if your haemoglobin is still in range. That's why iron deficiency can exist without anaemia, and why symptoms such as fatigue, hair thinning, restless legs and poor concentration deserve attention. One caveat: ferritin is an acute phase protein, so inflammation or infection can push it up and mask true deficiency.

One analogy that I like to use is the bank. Ferritin is your body's iron stores, your savings account. You want this nice and full in preparation for a rainy day. You withdraw iron from your ferritin to help make haemoglobin which carries oxygen around your body in your blood to the cells that need it.

Who's at higher risk?

•People with heavy periods

•Vegetarians and vegans

•Pregnant and postpartum women

•People with coeliac disease or other absorption conditions

•Frequent blood donors and endurance athletes

•People who restrict their intake, binge, vomit or purge

On that last point. Iron status can be surprisingly misleading in eating disorders. Dehydration can make haemoglobin look reassuringly normal, while stores quietly deplete. Restriction, reduced variety (often avoiding red meat), and purging behaviours all affect iron intake or loss. A "normal" result does not mean someone is nutritionally well, and results should always be read in the full clinical context.

Food-first strategies:

•Haem iron (red meat, poultry, fish) is absorbed most efficiently.

•Non-haem iron (pulses, tofu, fortified cereals, leafy greens, nuts and seeds) is absorbed better with vitamin C.

•Tea, coffee and calcium-rich foods can reduce absorption when taken with iron-rich meals, so space them apart where you can.

Supplements. Many people need more than diet can provide to rebuild stores. Alternate-day dosing is often as effective as daily and may be better tolerated, but this should be guided by your GP or dietitian. Please avoid self-prescribing high doses, as excess iron can be harmful and can cause significant gastrointestinal side effects.

The takeaway. Don't ignore persistent tiredness, and don't assume it's "just life". Ask for ferritin as well as haemoglobin to be checked, and work with a registered professional to understand the cause, not just the number.

This post is for general information and does not replace individual medical or dietetic advice.