How to counsel a patient with restless legs syndrome and impaired iron levels on avoiding iron intake before lab tests for accurate serum iron parameter measurements?

Patient Counseling on Avoiding Iron Before Lab Testing for RLS

Patients with restless legs syndrome must avoid ALL iron-containing supplements and foods for at least 24 hours before their morning blood draw to ensure accurate measurement of serum ferritin and transferrin saturation. 1, 2

Why This Matters for Your RLS Diagnosis and Treatment

• Iron studies are mandatory for all patients with clinically significant RLS because brain iron deficiency is a core pathophysiological mechanism of the disease, even when blood counts appear normal. 2, 3

• The American Academy of Sleep Medicine requires testing serum ferritin and transferrin saturation in the morning after avoiding iron-containing supplements and foods for at least 24 hours prior to blood draw. 1, 2

• Ferritin has diurnal variation (changes throughout the day), and recent iron intake can falsely elevate results, making it appear you have adequate iron stores when you actually don't. 2

• RLS-specific iron thresholds are completely different from general population guidelines: you need supplementation if ferritin ≤75 ng/mL or transferrin saturation <20%, which is much higher than standard anemia cutoffs. 1, 2

Specific Instructions for Your Patient

What to Avoid for 24 Hours Before Testing

Supplements to stop:

• All multivitamins containing iron 1, 2
• Iron supplements (ferrous sulfate, ferrous gluconate, iron bisglycinate, etc.) 1, 2
• Prenatal vitamins (these typically contain 27-30 mg iron) 2

Foods to avoid:

• Red meat (beef, lamb, pork) 1
• Organ meats (liver, kidney) 1
• Iron-fortified cereals and breads 1
• Dark leafy greens in large quantities (spinach, kale) 1
• Beans and lentils 1
• Iron-fortified plant-based milk 1

Testing Protocol

• Schedule the blood draw for early morning (ideally 7-9 AM) when ferritin levels are most stable. 2, 4

• Fast overnight if possible, though this is less critical than the 24-hour iron avoidance. 2

• Both ferritin AND transferrin saturation must be measured together because ferritin alone can be falsely elevated by inflammation (infections, arthritis, etc.), masking true iron deficiency. 2

Why Both Tests Are Required

• Transferrin saturation <20% indicates functional iron deficiency even when ferritin appears adequate, which is common in RLS patients. 2

• Inflammation can raise ferritin independent of true iron stores, so transferrin saturation provides a second checkpoint. 2

• The treatment decision (oral iron vs. IV iron vs. no iron) depends on BOTH values, not just one. 1, 2

What Happens After Testing

If ferritin ≤75 ng/mL OR transferrin saturation <20%:

• You will likely start oral ferrous sulfate or receive IV ferric carboxymaltose infusion. 1, 4

If ferritin is 75-100 ng/mL:

• Only IV iron (not oral) is recommended because oral absorption is poor in this range. 4

If ferritin >100 ng/mL with normal transferrin saturation:

• Iron supplementation is generally not indicated, and other RLS treatments will be prioritized. 4

Critical Pitfall to Avoid

• Do not assume that normal hemoglobin or "not being anemic" means your iron is adequate for RLS—42.3% of RLS patients without anemia have iron deficiency that requires treatment. 5

• Women are at 5.5 times higher risk for iron deficiency without anemia in RLS compared to men. 5

Long-Term Monitoring

• Even after starting treatment, iron studies should be rechecked every 6-12 months because RLS symptoms may recur if iron stores decline below therapeutic thresholds. 6, 7

• Continue avoiding iron for 24 hours before each follow-up blood draw to maintain accuracy. 1, 2