Is transferrin saturation typically included in an iron panel for a patient with restless legs syndrome and potential iron deficiency?

Is Transferrin Saturation Included in an Iron Panel?

Yes, transferrin saturation (TSAT) is a standard component of an iron panel and is calculated from serum iron and total iron binding capacity measurements. 1

What an Iron Panel Includes

A complete iron panel typically measures the following parameters:

• Serum iron - the amount of circulating iron bound to transferrin 1
• Total iron binding capacity (TIBC) - the maximum amount of iron that transferrin can bind 1
• Transferrin saturation (TSAT) - calculated as (serum iron ÷ TIBC) × 100, representing the percentage of transferrin binding sites occupied by iron 1
• Serum ferritin - reflects iron storage in the body 1

Why Both TSAT and Ferritin Matter for RLS

For patients with restless legs syndrome specifically, both transferrin saturation and ferritin serve complementary but distinct diagnostic purposes and must both be measured. 2

TSAT Identifies Functional Iron Deficiency

• TSAT <20% identifies functional iron deficiency even when ferritin appears adequate, revealing patients who need iron supplementation despite seemingly normal ferritin levels 2
• This is particularly important because TSAT reflects iron that is readily available for erythropoiesis and delivery to tissues, including the brain 1

Ferritin Can Be Misleading Alone

• 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 2
• Ferritin is an acute phase reactant that increases with acute or chronic inflammation, independent of actual iron stores 1

RLS-Specific Iron Thresholds

The American Academy of Sleep Medicine recommends iron supplementation for RLS patients when:

• Ferritin ≤75 ng/mL OR transferrin saturation <20% 1, 3, 2
• These thresholds are higher than general population guidelines (ferritin <12-30 ng/mL, TSAT <16%) because brain iron deficiency in RLS occurs at higher serum levels 3, 2, 4

Testing Protocol for RLS

• Blood should be drawn in the morning after avoiding all iron-containing supplements and foods for at least 24 hours prior to the blood draw 3, 2
• The full iron studies should include both serum ferritin and transferrin saturation 2

Clinical Pitfall to Avoid

Do not rely on ferritin alone to exclude iron deficiency in RLS patients. 2 A patient may have "normal" ferritin (e.g., 100 ng/mL) due to inflammation but still have TSAT <20%, indicating they cannot deliver adequate iron to the brain and would benefit from iron supplementation. 1, 2