Iron Studies for Restless Legs Syndrome Diagnosis and Treatment

Diagnostic Criteria

The American Academy of Sleep Medicine recommends checking both serum ferritin and transferrin saturation in all patients with clinically significant Restless Legs Syndrome (RLS) because these parameters serve different but complementary diagnostic purposes 1
Ferritin can be falsely elevated by inflammation, making it an unreliable sole indicator of iron status in RLS patients who may have concurrent inflammatory conditions 1
Transferrin saturation <20% identifies functional iron deficiency even when ferritin appears adequate, revealing patients who need iron supplementation despite seemingly normal ferritin levels 1

Oral or IV iron is indicated when ferritin is ≤75 ng/mL or transferrin saturation is <20% 1
IV iron only (not oral) is recommended when ferritin is 75-100 ng/mL 1
No iron supplementation is needed when ferritin is >100 ng/mL with adequate transferrin saturation 1

Blood should be drawn in the morning after the patient has avoided all iron-containing supplements and foods for at least 24 hours prior to the blood draw 1
The full iron studies should include serum ferritin and transferrin saturation (calculated from serum iron and total iron binding capacity) 1

Renal function (creatinine, eGFR) should be assessed to identify chronic kidney disease, which requires different RLS treatment algorithms 1
A complete blood count (CBC) should be performed to assess for overt anemia requiring more aggressive iron repletion 2