sTfR-F Index Calculator

What is the sTfR-F Index?

The soluble transferrin receptor to log ferritin ratio (sTfR-F Index) is a highly effective tool for differentiating between iron deficiency anemia (IDA) and anemia of chronic disease (ACD), especially in complex cases where both may coexist.

sTfR levels increase when cellular iron is deficient, while ferritin levels decrease. In contrast, in ACD, sTfR levels are typically normal while ferritin (an acute-phase reactant) can be normal or high. This index leverages these opposing responses to provide a powerful diagnostic clue.

Why is this Index Superior?

• More accurate than using either sTfR or ferritin alone, particularly in patients with inflammation.
• Helps avoid unnecessary iron therapy in patients with ACD, where iron supplementation can be ineffective or even harmful.
• Identifies functional iron deficiency in patients with chronic illness, where iron stores are present but unavailable for erythropoiesis.

Interpreting the Result (Reference Guide)

Clinical Application

This index is a sophisticated tool intended for use by healthcare professionals. Its interpretation requires consideration of the full clinical context.

• The cut-off value of 1.5 is widely validated for differentiating IDA from ACD.
• Values can be influenced by renal function and erythropoietic activity.
• It is particularly useful when serum ferritin falls into the ambiguous 30-100 µg/L range.
• Always correlate with other hematological parameters and clinical findings.