Ferritin Explained: Your Iron Stores

When people think about iron, they usually picture the iron travelling in their blood. But your body also keeps iron in reserve, and the protein that stores it is called ferritin. Measuring ferritin tells you how much iron you have banked away — which is why it is often the first marker to fall when iron starts running short.

What ferritin is

Ferritin is a storage protein that holds iron in a safe, available form inside your cells, mainly in the liver, spleen and bone marrow. A blood ferritin test estimates the size of this reserve. Think of it as the balance in your iron savings account: when you take in less iron than you use, you draw down these stores first, before the iron in your circulating blood is affected.

Why ferritin is the earliest warning sign

Because stores are depleted before your blood count changes, ferritin can flag iron deficiency well before anaemia appears. Someone can feel tired, run down or short of breath with a normal haemoglobin but a low ferritin — a stage sometimes described as iron deficiency without anaemia. Catching it early means it can be addressed before it progresses.

Signs your iron stores may be low

Low ferritin can produce symptoms even when a standard blood count looks normal. Common ones include:

• Persistent tiredness and low energy
• Breathlessness or a racing heart on exertion
• Pale skin, brittle nails or hair thinning
• Poor concentration and reduced exercise tolerance
• Restless legs, particularly at night

These are non-specific, so a blood test is the reliable way to confirm whether low iron stores are behind them.

An important limitation

Ferritin has one quirk worth knowing: it is also an inflammatory marker, meaning it can rise when there is infection, inflammation or other illness in the body. This can occasionally mask a genuine iron deficiency by pushing the ferritin figure into the normal range. For that reason, ferritin is best interpreted alongside a full blood count and, where relevant, markers of inflammation such as CRP, so the result is read in context rather than on its own.

Who should consider a ferritin test

Checking ferritin can be worthwhile if you have unexplained fatigue, heavy periods, a vegetarian or vegan diet, are a regular blood donor, are pregnant or planning pregnancy, or take part in endurance exercise. It is also a sensible check when investigating hair loss. If your ferritin is low, your clinician will look for the underlying cause — because finding out why your stores are dropping matters as much as topping them back up.

Written by Dr Ibrar Ahmed — MBChB MRCP MRCGP PhD PG Dip (Cardiology)
Specialist interest: Cardiovascular Medicine · OneMedicine, CQC-registered clinic