Iron Studies Updated Apr 17, 2026

Soluble Transferrin Receptor (sTfR)

Soluble Transferrin Receptor (sTfR) is a lab value that reflects how much transferrin receptor is present in a soluble form in blood. The sTfR result is often used in Iron Studies to add context to red cell production and iron use on a lab report or blood test.

What Is Soluble Transferrin Receptor (sTfR)?

Soluble Transferrin Receptor (sTfR) is a measured blood value that reflects the amount of transferrin receptor found in a soluble form in the bloodstream. In practical terms, sTfR gives a snapshot of how active red blood cell production is and how strongly cells are pulling in iron. On a lab report, Soluble Transferrin Receptor on a lab report is usually read as part of Iron Studies rather than as a stand-alone value. The sTfR test is reported as a concentration, so the number depends on the lab method and the unit used.

Why Is Soluble Transferrin Receptor (sTfR) Tested?

The sTfR test is commonly included in Iron Studies to add context to other iron-related markers such as ferritin and serum iron. Soluble Transferrin Receptor on a blood test can help describe whether the body is making more transferrin receptor as red cell production changes. It is not usually part of a CBC or CMP, but it is often ordered alongside other blood values when a fuller picture of iron use is needed. In this setting, the sTfR result helps compare iron supply, iron use, and red cell turnover.

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Soluble Transferrin Receptor (sTfR) Normal Range

Group Range Unit
Adult Male 2.2–5 mg/L
Adult Female 2–4.9 mg/L

Reference ranges may vary by laboratory and individual factors.

What Does High sTfR Mean?

High sTfR usually means the body is making and releasing more transferrin receptor into the blood, which often reflects stronger demand for iron by developing red blood cells. On a Soluble Transferrin Receptor test result, values above the lab's reference interval are commonly read as high sTfR, and some labs use cutoffs around 4.4 mg/L or similar depending on the assay. A high sTfR on a lab report can also appear when the balance between iron supply and iron use is shifted toward higher cellular demand. The exact interpretation depends on the lab method and the rest of the Iron Studies panel.

Associated factors

Low iron intake — less iron available for red cell building can increase sTfR production as cells respond to demand.
Recent blood loss — replacement of lost red cells can raise sTfR as marrow activity increases.
Pregnancy — expanded blood volume and higher red cell demand can increase sTfR.
Growth spurts — faster tissue growth can increase iron use and raise sTfR.
High-altitude exposure — lower oxygen levels can stimulate red cell production and increase sTfR.
Endurance exercise — sustained training can increase red cell turnover and shift sTfR upward.
Smoking — chronic low oxygen exposure can increase red cell production and raise sTfR.
Low body iron stores — depleted iron supply commonly tracks with high sTfR.
Certain supplements or medications — products that alter iron absorption or red cell turnover can change sTfR levels.

What Does Low sTfR Mean?

Low sTfR means there is less soluble transferrin receptor in the blood than expected for that lab's reference interval. On a Soluble Transferrin Receptor test result, a low sTfR is often read as reduced demand for iron by developing red blood cells or lower red cell production activity. In some settings, low sTfR can occur when the marrow is less active or when the body is not signaling for more iron uptake. Interpretation depends on the full Iron Studies pattern, including ferritin and serum iron.

Associated factors

Low red cell production rate — fewer developing red cells can reduce the amount of soluble receptor released.
Recent iron repletion — improved iron availability can lower sTfR as demand drops.
Short-term inflammation — acute shifts in blood proteins can sometimes reduce measured sTfR.
Chronic undernutrition — reduced overall protein and iron intake can alter marrow activity and lower sTfR.
Hormonal changes — shifts in growth or reproductive hormones can influence red cell turnover.
Certain medications — drugs that affect marrow activity or iron handling can reduce sTfR.
Advanced age — average marrow activity may be lower, which can track with low sTfR in some people.
Laboratory method differences — some assays read lower than others, especially near the reference limit.

How Soluble Transferrin Receptor (sTfR) Relates to Other Values

sTfR is often reviewed with ferritin, serum iron, transferrin, transferrin saturation, and CBC markers such as hemoglobin (Hgb), hematocrit (Hct), mean corpuscular volume (MCV), and red blood cell count (RBC). When sTfR is read alongside ferritin, the pattern helps show whether circulating iron supply and stored iron point in the same direction or different directions. When sTfR is paired with MCV and Hgb, the combination helps describe whether red cells are smaller or larger than typical and how much protein they carry. On an Iron Studies panel, this comparison is more informative than any one value alone.

What Factors Affect Soluble Transferrin Receptor (sTfR) Levels?

Age, sex, body size, and red cell turnover can shift sTfR within a normal Soluble Transferrin Receptor reference range. Men and women may have slightly different averages, and pregnancy can push values upward because of higher blood volume and iron use. Altitude, smoking, recent exercise, hydration status, and time of day can all influence the measured Soluble Transferrin Receptor test result to a small degree. Different lab methods and antibody-based assays can report different absolute numbers, so the same sample may not match across laboratories. Diet patterns and recent iron intake also matter, especially when sTfR is interpreted with ferritin and transferrin saturation.

How It Is Tested

The sTfR test is done on a blood sample drawn from a vein. The lab measures soluble transferrin receptor concentration in serum or plasma, depending on the method used. Results are usually reported in mg/L, but some laboratories may use other units.

How to Prepare

No fasting is usually required for the sTfR test as part of Iron Studies. The result can be interpreted with the rest of the panel in the same sample.

Frequently Asked Questions

What is the normal range for Soluble Transferrin Receptor?
The Soluble Transferrin Receptor normal range depends on the lab method, but many US references place sTfR around 2.2 to 5.0 mg/L for adult men and 2.0 to 4.9 mg/L for adult women. The exact Soluble Transferrin Receptor reference range on a lab report should match the laboratory that ran the sTfR test.
What does sTfR stand for?
sTfR stands for soluble transferrin receptor. It is the shortened name used on many lab reports and Iron Studies panels.
What is a high Soluble Transferrin Receptor mean on a lab report?
A high sTfR on a lab report usually means the body is making more soluble transferrin receptor than expected for that reference range. This often reflects increased iron demand by developing red blood cells, and the result is best read with ferritin, serum iron, and transferrin saturation.
What does a low Soluble Transferrin Receptor mean on a lab report?
A low sTfR on a lab report usually means less soluble transferrin receptor is being released into blood than expected. It can reflect lower red cell production activity, recent iron repletion, or normal variation around the lab's reference interval.
Can exercise affect Soluble Transferrin Receptor?
Yes. Exercise can affect sTfR slightly, especially with frequent endurance training or recent heavy activity. These shifts are usually smaller than changes seen from iron balance or red cell production patterns.
What is the difference between Soluble Transferrin Receptor and ferritin?
sTfR reflects how strongly developing red blood cells are pulling in iron, while ferritin reflects stored iron. The two markers are often read together on an Iron Studies panel because the combination gives a fuller picture than either value alone.
What unit is Soluble Transferrin Receptor measured in?
sTfR is commonly reported in mg/L. Some laboratories may use different units or assay-specific reference ranges, so the unit on the lab report matters.
How much can Soluble Transferrin Receptor change between tests?
sTfR can change modestly between tests because of lab method differences, hydration, exercise, and shifts in red cell production. Small changes near the reference limit may fall within normal biological variation.
Is Soluble Transferrin Receptor different for men and women?
Yes, the Soluble Transferrin Receptor normal range can differ slightly between men and women. That is why many lab reports list separate reference intervals for adult male and adult female results.
Why is Soluble Transferrin Receptor tested in an Iron Studies panel?
sTfR is included in Iron Studies because it adds a measure of red cell iron demand to the panel. On a blood test, that helps interpret ferritin, serum iron, and transferrin saturation together.
What does sTfR mean on a blood test?
On a blood test, sTfR means soluble transferrin receptor. It is a blood marker that helps describe iron use and red cell production activity on the lab report.

Disclaimer

This content is for informational and educational purposes only. It is not intended as medical advice, diagnosis, or treatment recommendation. Reference ranges may vary by laboratory. Always discuss your results with a qualified healthcare professional.

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