Iron — Ferritin, Serum Iron & Transferrin Saturation
Iron is an essential mineral. Our bodies need it to produce hemoglobin, the protein in red blood cells that carries oxygen throughout the body. Iron also supports muscle function, energy production, and brain health.
Both too little and too much iron can cause health problems.
Iron testing is particularly important for older adults because fatigue, weakness, and anemia are common, but their causes are not always obvious.
A single iron test rarely tells the whole story. Doctors often examine several measurements together to determine whether the body has too little iron, too much iron, or difficulty using the iron it already has.
Ferritin — How Much Iron Is Stored?
Ferritin is a protein that stores iron inside cells. A blood ferritin test provides an estimate of the body's iron reserves.
When ferritin is low, iron stores are usually depleted.
Approximate interpretations include:
Below 15 ng/mL: Strong evidence of depleted iron stores.
15–30 ng/mL: Iron deficiency is likely.
30–45 ng/mL: May still indicate iron deficiency, particularly when anemia is present.
Above 45 ng/mL: Iron deficiency becomes less likely in otherwise healthy people, but it is not ruled out.
The American Gastroenterological Association recommends using a ferritin threshold of 45 ng/mL when diagnosing iron deficiency in people who have anemia.
Laboratory reference ranges vary, and the significance of a ferritin result depends on the person's health and other blood tests.
Why Can Ferritin Be High?
Ferritin has an important complication: it is also a marker that can increase during inflammation.
High ferritin does not necessarily mean the body has too much iron.
Possible causes include:
Chronic inflammation or infection
Metabolic dysfunction and fatty liver disease
Liver disease
Excessive iron accumulation
Certain cancers and other illnesses
For example, someone with metabolic dysfunction-associated steatotic liver disease (MASLD), formerly called fatty liver disease, may have elevated ferritin without having excessive iron stores.
This is why ferritin should not be interpreted alone.
Serum Iron — How Much Iron Is Circulating?
Serum iron measures the amount of iron circulating in the bloodstream, mostly attached to a transport protein called transferrin.
A typical laboratory reference range is approximately 60–170 µg/dL, although ranges vary.
Serum iron can change considerably depending on:
Time of day
Recent meals
Iron supplements
Inflammation or illness
A low serum iron result does not automatically establish iron deficiency.
Likewise, a normal serum iron level does not guarantee that iron stores are adequate.
Transferrin Saturation — How Much Iron Is Available?
Transferrin is the protein that transports iron through the bloodstream.
Transferrin saturation (TSAT) measures the percentage of transferrin's iron-binding capacity that is occupied by iron.
It is calculated using serum iron and total iron-binding capacity (TIBC).
Typical interpretations include:
Below 20%: May suggest insufficient available iron.
20–45%: Often within the usual range.
45% or higher: May suggest excessive iron absorption or accumulation and deserves further evaluation if persistent.
These are approximate guidelines rather than universal diagnostic cutoffs.
Transferrin saturation is particularly helpful when ferritin is elevated because of inflammation.
For example, someone may have normal or elevated ferritin but low transferrin saturation, suggesting that iron is not readily available for producing red blood cells.
What Is TIBC?
Total iron-binding capacity (TIBC) estimates how much iron the blood's transport proteins could carry.
It is commonly included in an iron panel.
In general:
High TIBC: Often accompanies iron deficiency.
Low or normal TIBC: May occur with inflammation, liver disease, or other conditions.
TIBC is most useful when interpreted alongside serum iron and transferrin saturation.
Iron Deficiency and Anemia
Iron deficiency is one of the most common causes of anemia.
Symptoms may include:
Fatigue and weakness
Shortness of breath during activity
Dizziness
Reduced exercise tolerance
Pale skin
Restless legs
However, iron deficiency can develop before anemia becomes apparent on a complete blood count.
In older adults, iron deficiency deserves particular attention because it may reflect chronic blood loss rather than inadequate dietary iron.
Possible causes include gastrointestinal bleeding, ulcers, polyps, colorectal cancer, and medications that increase bleeding risk.
The American Gastroenterological Association recommends gastrointestinal evaluation, generally including colonoscopy and upper endoscopy, for men and postmenopausal women with confirmed iron deficiency anemia, with decisions individualized to the patient's circumstances.
Simply taking an iron supplement without investigating unexplained iron deficiency can delay the diagnosis of an important underlying condition.
Anemia of Chronic Inflammation
Not all anemia results from insufficient iron stores.
In chronic inflammation, the body produces more of a hormone called hepcidin, which reduces iron absorption and limits the release of stored iron into the bloodstream.
As a result, a person may have:
Low serum iron
Low transferrin saturation
Normal or elevated ferritin
The body has iron, but it is less available for red blood cell production.
This pattern can occur with chronic kidney disease, autoimmune disorders, infections, and other inflammatory conditions.
Treatment generally focuses on the underlying illness, although iron treatment may also be appropriate in selected circumstances.
What About Too Much Iron?
Excessive iron accumulation can damage the liver, heart, pancreas, and other organs.
One important cause is hereditary hemochromatosis, a genetic condition that increases iron absorption.
Possible clues include:
Persistently elevated transferrin saturation
Elevated ferritin
Abnormal liver tests
A family history of iron overload
A transferrin saturation of 45% or higher may prompt further testing, including repeat iron studies and sometimes genetic testing.
However, elevated ferritin alone is not enough to diagnose hemochromatosis.
When significant iron overload is confirmed, treatment often involves periodically removing blood, a procedure called therapeutic phlebotomy.
Should Older Adults Take Iron Supplements?
Iron supplements can be very helpful when iron deficiency has been established.
However, iron is not a supplement that everyone should take routinely.
Excess iron can be harmful, and supplementation may cause constipation, nausea, and abdominal discomfort.
Treatment depends on the cause and severity of deficiency. Oral iron is commonly used, while intravenous iron may be appropriate for people with poor absorption, certain chronic illnesses, or intolerance of oral supplements.
An important consideration is that taking more iron does not necessarily improve energy when iron levels are already adequate.
The Bottom Line
Ferritin, serum iron, and transferrin saturation measure different aspects of iron metabolism.
Ferritin helps estimate stored iron, while serum iron and transferrin saturation provide information about circulating and available iron.
Low ferritin strongly suggests iron deficiency. High ferritin is more complicated because it may reflect inflammation, liver disease, metabolic dysfunction, or iron overload.
For older adults, identifying the cause of iron deficiency is often as important as correcting it.
The most useful interpretation comes from considering these tests together with the complete blood count, medical history, and other laboratory findings.
Learn More
Explains iron's role in the body, iron deficiency, recommended intake, and the risks of excessive supplementation.
Recommendations for diagnosing iron deficiency anemia and investigating possible gastrointestinal causes, particularly in older adults.
A useful explanation of serum iron, ferritin, transferrin, and other tests used to evaluate iron status.