If you have restless legs at night, the key clue is a pattern: an urge to move that starts or worsens when you rest, eases while you move, and is usually worse in the evening. A clinician may also check ferritin and transferrin saturation, because iron results can affect whether iron treatment is considered—even if your blood count is normal. The tests do not diagnose restless legs syndrome on their own.
How Clinicians Distinguish Restless Legs
Restless legs syndrome (RLS), also called Willis-Ekbom disease, is diagnosed from your symptoms and whether they meet specific criteria. The core features are an urge to move the legs, often with unpleasant sensations; symptoms that begin or worsen during rest; at least temporary relief with movement; and symptoms that occur only, or are worse, in the evening or at night. The pattern should not be explained solely by another condition.
That last step matters because leg discomfort has many possible causes. A cramp is often a sudden, painful tightening of a muscle; pressure from a position may ease when you shift. RLS is more specifically an urge to move, often with sensations described as creeping, pulling, tingling or itching. These distinctions can help you describe what happens, but symptoms can overlap, so a clinician may need to consider other explanations.
Before an appointment, note when symptoms start, what rest or movement does to them, and whether they disrupt sleep. Mention any similar symptoms in your arms, medicines you take, and relevant conditions such as pregnancy, kidney disease or neuropathy.
Why Ferritin Matters Even With a Normal Blood Count
A complete blood count (CBC) checks, among other things, for anaemia; it does not give the same information as iron studies. Ferritin is a marker of stored iron, while transferrin saturation (TSAT) estimates how much iron is available in the blood. A normal haemoglobin result does not rule out low iron stores or establish that iron levels are adequate for someone with RLS.
Iron is linked to RLS, but a blood test cannot directly measure iron in the brain, where iron regulation may also matter. So these results inform a treatment decision; they do not prove what is causing an individual’s symptoms. Iron stores can fall before haemoglobin does; you can read more about iron levels before anaemia.
The American Academy of Sleep Medicine’s 2025 clinical practice guideline says clinicians should regularly check iron studies in people with clinically significant RLS. Its task force based recommendations on a systematic review and graded the certainty of evidence. The guideline says testing is ideally done in the morning, avoiding iron-containing food and supplements for at least 24 hours beforehand. Ask your clinician or laboratory how to prepare, especially if you already take prescribed iron.
Which Results May Lead to Iron Treatment?
For adults with RLS, the AASM guideline gives consensus thresholds—not thresholds empirically tested as a rule for every patient. It suggests considering oral or intravenous (IV) iron when ferritin is 75 ng/mL (75 µg/L) or lower, or TSAT is below 20%. When ferritin is between 75 and 100 ng/mL (µg/L), its guidance is to use IV iron only. These are RLS-specific considerations and differ from general iron reference ranges; the laboratory’s “normal” label alone may not answer the question.
The result is one part of the decision. A clinician may consider your full iron panel, symptoms, medical history and whether oral iron is suitable. In children, the guideline uses a different ferritin threshold: below 50 ng/mL (µg/L). Pregnancy and end-stage kidney disease also need specific clinical consideration, so adult thresholds should not be applied to those situations without professional advice.
Why You Shouldn’t Start Iron on Your Own
Symptoms alone cannot tell you whether iron is low, and taking iron without testing and guidance may be inappropriate. The right approach depends on the results and circumstances; oral and IV treatment are not interchangeable. Ask whether ferritin and TSAT have been checked and how the results fit together before starting a supplement or changing a dose.
Iron is not the only factor to review. The AASM identifies alcohol, caffeine, some antihistamine, serotonergic and antidopaminergic medicines, and untreated obstructive sleep apnoea as possible symptom-worsening factors. Do not stop a prescribed medicine on your own; ask the prescriber whether it could contribute and whether an alternative or adjustment is appropriate. Some dopamine-related medicines used for RLS can also cause symptoms to worsen over time, a problem clinicians call augmentation.
If symptoms regularly disturb your sleep, discuss the symptom pattern, medicines and iron studies with a clinician. Seek medical advice rather than self-treating, particularly if you are pregnant, have kidney disease, or are considering iron supplements for a child.
