Ferritin and transferrin saturation: what to ask your doctor to test

Iron in the brain is closely tied to restless legs syndrome, and correcting low iron is one of the most useful things that can be done about it. A routine physical often does not include the right tests, and "normal" on a lab report is not the same as adequate for RLS.

Which tests to ask for

• Ferritin, a measure of the body's iron stores.
• Transferrin saturation (TSAT), how much of your iron-carrying capacity is filled. This one is easy to leave off, so ask for it specifically.

A hemoglobin or general "iron level" alone does not tell the RLS story. Ferritin and transferrin saturation together do.

Target levels

The 2024 guideline discusses aiming for a ferritin above 100 ng/mL and a transferrin saturation above 20%. That ferritin target is higher than the lab's "normal" floor, which is why many people are told their iron is fine when it is not yet where it needs to be for restless legs.

When to test

Ferritin can read falsely high when the body is fighting an infection or inflammation, so a value drawn while you are sick may be misleading. It is reasonable to ask when the best time to test is.

If your iron is low

There is more than one way to raise iron, from oral supplements to intravenous (IV) iron, and the right choice depends on your labs and your body. That decision belongs with your doctor, but you can arrive already knowing which tests to ask for and what the targets are.