Iron Panel and Ferritin Testing for RLS
No, ordering only an iron panel and ferritin is insufficient—you must order both serum ferritin AND transferrin saturation (calculated from serum iron and total iron binding capacity), as these serve complementary diagnostic purposes and both are required by the American Academy of Sleep Medicine guidelines. 1
Why Both Tests Are Essential
- Ferritin alone is unreliable because it can be falsely elevated by inflammation, making it an inadequate 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
- The American Academy of Sleep Medicine explicitly recommends checking both parameters in all patients with clinically significant RLS 1, 2
Proper Testing Protocol
Blood draw timing and preparation are critical:
- Draw blood in the morning after the patient has avoided all iron-containing supplements and foods for at least 24 hours prior 1, 2
- Ferritin has diurnal variation and recent iron intake can falsely elevate results 3
- This standardized approach prevents misclassification of iron status 3
Treatment Thresholds Based on Results
The American Academy of Sleep Medicine provides specific treatment algorithms based on combined ferritin and transferrin saturation values 4, 1:
- Ferritin ≤75 ng/mL OR transferrin saturation <20%: Use oral or IV iron 1, 2
- Ferritin 75-100 ng/mL: Use ONLY IV iron (not oral) 1, 2
- Ferritin >100 ng/mL with adequate transferrin saturation: No iron supplementation needed 1
Additional Recommended Testing
Beyond iron studies, you should obtain 3:
- Complete blood count (CBC) to assess for overt anemia requiring more aggressive iron repletion 1, 3
- Renal function (creatinine, eGFR) to identify chronic kidney disease, which requires different RLS treatment algorithms and has different iron supplementation thresholds 1, 3
Common pitfall: Ordering ferritin alone will miss patients with functional iron deficiency who have adequate ferritin but low transferrin saturation (<20%), leading to undertreatment of a correctable cause of RLS 1. The iron thresholds for RLS are different from the general population—ferritin up to 75 ng/mL warrants supplementation in RLS, whereas this would be considered adequate in non-RLS patients 4, 2.