Soluble Transferrin Receptor (sTfR) Unit Converter

Soluble Transferrin Receptor (sTfR) Unit Converter

Convert soluble transferrin receptor between mg/L, µg/mL and nmol/L, with the caveat that reference ranges are assay-specific.

Last updated 31 Aug 2026

Soluble Transferrin Receptor (sTfR) converter

Mass ⇄ molar
Results are not transferable between manufacturers — use your own laboratory's range.
Ranges are laboratory-specific; confirm against your own report.
40.1nmol/LExample

sTfR 3.4 mg/L

Formula and conversion factor

nmol/L = mg/L × 11.81
mg/L = µg/mL (numerically identical)
11.81
derived from a soluble receptor molecular weight of ≈84,700 Da
assay
Roche, Siemens and in-house methods report on different scales — do not compare across platforms

Worked example

sTfR 3.4 mg/L
3.4 × 11.81 = 40.1 nmol/L
3.4 mg/L = 3.4 µg/mL

Typical adult intervals by platform

AssayReference intervalUnits
Roche Tina-quant2.2 – 5.0mg/L
Siemens nephelometric0.76 – 1.76mg/L
WHO reference reagentharmonisedmg/L
The absence of a universal calibrator is the main practical limitation of sTfR. Always quote the platform alongside the result.

What sTfR measures

Soluble transferrin receptor is a fragment shed from the surface of developing red cells. Its concentration reflects two things at once: the total mass of erythroid precursors, and how iron-starved those precursors are. When cells cannot get enough iron they upregulate surface receptor, and more of it appears in plasma.

The clinical appeal is that sTfR is not an acute-phase reactant. Where ferritin rises with inflammation and can mask iron deficiency entirely, sTfR stays interpretable, which makes it valuable in exactly the patients where the standard panel fails — chronic kidney disease, inflammatory bowel disease, rheumatoid arthritis, malignancy.

Two caveats limit it. Because it also tracks erythroid mass, sTfR rises in haemolysis, thalassaemia and after erythropoietin therapy regardless of iron status, and falls in marrow failure. And there is no universal calibration: the numerical result from one manufacturer’s assay cannot be compared with another’s. In practice it is most useful combined with ferritin as the sTfR–ferritin index rather than read alone.

Frequently asked questions

Why does sTfR work when ferritin does not?

Ferritin is an acute-phase reactant and rises with inflammation, which can hide iron deficiency. Soluble transferrin receptor is not affected by the acute-phase response, so it stays interpretable in inflamed patients.

Can I compare sTfR results from different laboratories?

Not reliably. There is no universally adopted calibrator, and reference intervals differ several-fold between manufacturers. Always interpret against the range supplied by the reporting laboratory.

What raises sTfR apart from iron deficiency?

Anything that expands the erythroid marrow: haemolytic anaemia, thalassaemia, recovery from blood loss, high-altitude residence and erythropoietin therapy. Marrow failure and chronic kidney disease without EPO lower it.

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References

  1. WHO. Serum transferrin receptor levels for the assessment of iron status. Geneva, 2020.
  2. Punnonen K et al. Serum transferrin receptor and its ratio to serum ferritin in the diagnosis of iron deficiency. Blood. 1997;89(3):1052–7.

Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.