Iron Panel Ordering for RLS: What You Need to Know
Yes, you are correct that an iron panel typically includes transferrin saturation, but you must verify your specific laboratory's iron panel components and order ferritin separately if it is not included, as both ferritin AND transferrin saturation are mandatory for proper RLS iron assessment. 1
Critical Testing Requirements
The American Academy of Sleep Medicine mandates checking both serum ferritin and transferrin saturation in all patients with clinically significant RLS because these parameters serve different but complementary diagnostic purposes. 1
Why Both Tests Are Essential
- 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
- Without both parameters, you will miss patients with functional iron deficiency who have adequate ferritin but low transferrin saturation 1
Laboratory Ordering Strategy
Verify Your Lab's Iron Panel Contents
Most hospital and commercial laboratories include the following in a standard "iron panel":
- Serum iron
- Total iron binding capacity (TIBC)
- Transferrin saturation (calculated from iron/TIBC)
However, ferritin is frequently NOT included in the standard iron panel and must be ordered separately. 1
Recommended Approach
Order both:
- Iron panel (to obtain transferrin saturation)
- Serum ferritin (as a separate test)
This ensures you capture all required parameters regardless of your laboratory's specific panel composition. 1
Proper Testing Protocol
Timing and Preparation
- Draw blood 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
- Ferritin has diurnal variation, and recent iron intake can falsely elevate results 2
RLS-Specific Treatment Thresholds (Different from General Population)
Iron supplementation is indicated when: 3, 1, 4
- Ferritin ≤75 ng/mL (oral or IV iron)
- Transferrin saturation <20% (oral or IV iron)
- Ferritin 75-100 ng/mL (IV iron only, not oral)
No iron supplementation needed when:
- Ferritin >100 ng/mL with adequate transferrin saturation 1
Additional Screening Considerations
Beyond the iron studies, obtain: 1, 2
- Renal function (creatinine, eGFR) to identify chronic kidney disease, which requires different RLS treatment algorithms
- Complete blood count (CBC) to assess for overt anemia requiring more aggressive iron repletion
Common Pitfall to Avoid
Do not order ferritin alone. 1 This is the most common error in RLS iron assessment. Patients with normal or elevated ferritin but low transferrin saturation (<20%) still have functional iron deficiency and will benefit from iron supplementation, but you will miss this entirely if you only check ferritin. 1