Soluble Transferrin Receptor

Iron Studies marker

Soluble Transferrin Receptor

Category: Iron Studies
Unit: mg/L

Reflects total erythropoietic activity and cellular iron demand. Unlike ferritin, it is NOT affected by inflammation, making it the most reliable iron marker in inflammatory states.

PED Notes

The most valuable iron marker for AAS users because unlike ferritin, it is NOT an acute phase reactant — unaffected by inflammation, liver stress from oral AAS, or intense training. When ferritin appears normal but the athlete has iron deficiency symptoms (fatigue, poor recovery), sTfR reveals whether tissue iron demand is being met. The sTfR/log ferritin index (sTfR ÷ log10 ferritin) >1.8 indicates iron-deficient erythropoiesis — this should be the gold standard for AAS users who donate blood regularly.

When elevated (>1.8 mg/L standard; >2.5 mg/L on AAS):

Elevated sTfR indicates tissue iron demand exceeds supply:

Step 1: Calculate sTfR/log ferritin index:

  • sTfR (mg/L) ÷ log10(Ferritin in ug/L)
  • Index >1.8 = iron-deficient erythropoiesis (functional iron deficiency)
  • Index >2.0 = high probability of true iron deficiency even if ferritin appears "normal"

Step 2: Differentiate the cause:

  • True iron deficiency (low ferritin + high sTfR): Iron stores depleted — most common from blood donation
  • Functional iron deficiency (normal/high ferritin + high sTfR): Iron trapped in stores due to inflammation. Ferritin is misleadingly elevated as an acute phase reactant
  • Increased erythropoietic drive (AAS use): Mildly elevated sTfR (1.8-2.5 mg/L) from stimulated bone marrow. If >2.5 mg/L, supplement iron regardless

Supplements:

  • Iron Bisglycinate -- 25-50mg elemental iron/day with Vitamin C 500mg
  • Lactoferrin -- 200mg/day (enhances iron absorption independent of hepcidin)
  • For functional iron deficiency with high ferritin: address inflammation first — reduce hepatotoxic oral AAS, reduce training volume if overreaching

Monitoring:

  • Recheck sTfR and full iron panel 6-8 weeks after starting supplementation
  • Target: sTfR within 0.8-1.8 mg/L (or 0.8-2.5 mg/L if on AAS) with ferritin >50 ug/L

References:

  • Skikne, B. S., Flowers, C. H., & Cook, J. D. (1990). Serum transferrin receptor: A quantitative measure of tissue iron deficiency. Blood, 75(9), 1870-1876. DOI: 10.1182/blood.V75.9.1870.1870
  • Punnonen, K., Irjala, K., & Rajamaki, A. (1997). Serum transferrin receptor and its ratio to serum ferritin in the diagnosis of iron deficiency. Blood, 89(3), 1052-1057. DOI: 10.1182/blood.V89.3.1052
  • Camaschella, C. (2015). Iron-deficiency anemia. New England Journal of Medicine, 372(19), 1832-1843. DOI: 10.1056/NEJMra1401038

History Chart

Reading History

Frequently Asked Questions

Reference Ranges

Standard Range

0.8 - 1.8 mg/L

VitalMetrics Range

0.8 - 2.5 mg/L

Statistics