Transferrin Saturation
The percentage of your blood's iron-carrying protein that is loaded with iron right now, worked out from serum iron and TIBC.
AI-verified against cited sources. Awaiting expert reviewAlso called TSATLOINC 2502-3
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What it is
Transferrin is the protein that carries iron in your blood. Transferrin saturation tells you how full it is. The lab calculates it by dividing serum iron by total iron-binding capacity (TIBC) and multiplying by 100. A low percentage means little iron is available for your body to use. A high percentage means the carrier protein is crowded with iron.
Why it matters
Doctors use transferrin saturation together with ferritin to look at both too little and too much iron. A low value, below about 20%, fits with low iron or with iron being held back by inflammation. A value that stays high, about 45% or more, is the usual first clue to iron overload and often leads to more testing. Serum iron swings during the day, so a single result can mislead.
If it’s low
A low transferrin saturation means little iron is available to make red blood cells. It is seen with low iron stores, and also in long-term inflammation or illness, where iron is held back in storage.
Common causes
- Low iron stores from heavy periods, other blood loss, pregnancy or too little iron in the diet
- Poor iron absorption
- Inflammation, infection or other long-term illness
- Chronic kidney disease or heart failure, where low iron is common
- Slow bleeding in the stomach or bowel
What can help
- Ask your clinician to read it together with ferritin, serum iron and TIBC
- Ask what may be behind it and whether iron treatment is right for you
- Eat iron-rich foods such as meat, fish, beans, lentils and iron-fortified cereals
If it’s high
A high transferrin saturation is often temporary, because it comes from serum iron, which rises after iron pills or an iron-rich meal. If it stays high on a repeat test, it can be a sign that the body is absorbing or holding too much iron, and your clinician may look into it further.
Common causes
- Iron pills or a multivitamin with iron taken shortly before the test
- A recent iron-rich meal
- Recent iron injections or blood transfusions
- Liver conditions such as hepatitis
- Hemolytic anemia or other blood disorders such as thalassemia
- Iron overload conditions, including the inherited condition hemochromatosis
- Iron poisoning from swallowing iron pills, which is an emergency
What can help
- Ask about repeating the test on a fasting morning sample, since guidelines suggest confirming a high value with a second sample
- Ask whether ferritin and liver tests should be checked at the same time
- Share any family history of iron overload with your clinician
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 15–55 %. Source: Labcorp, ARUP Laboratories, MedlinePlus Medical Encyclopedia (NIH).
- Adults (this one applies)15–55 %
Sources: Labcorp, ARUP Laboratories, MedlinePlus Medical Encyclopedia (NIH)
See TSAT by age and sex, with the U.S. survey numbers where they exist.
BSG 2021 (<20%) and AASLD 2011 (≥45%) decision points for transferrin saturation (adults)
- Below 20%: iron restrictedbelow 20 %
- Between the decision points20 to under 45 %
- 45% or higher: AASLD level for further testing45 and above %
If this applies to you
TSAT means a little more for some people. Open the one that fits you.
Endurance athlete
Transferrin saturation shows how much iron is moving in the blood right now. The Australian Institute of Sport lists it with ferritin and hemoglobin as the minimum iron checks for athletes.
Hemochromatosis or iron overload
Raised transferrin saturation is the hallmark of hemochromatosis. ACG calls it the preferred first test and notes that fasting isn't needed for it, though a few people, such as younger people early in the condition, can still have results below the usual threshold.
Low iron or anemia
BSG notes that transferrin saturation can help when ferritin may be falsely normal, for example during inflammation. A low value is one of the standard blood signs of iron deficiency.
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2017-March 2020 (pre-pandemic). Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore TSAT by age and sex: every percentile as a table, with a download.
What can affect your result
- Everything that affects serum iron: time of day, recent iron pills or meals, infection and inflammation
- Pregnancy and estrogen-containing birth control, which change TIBC
- Whether the lab calculates it from TIBC or from measured transferrin
- Iron treatment or a transfusion shortly before the draw
- Sex and menopause status, which some guideline thresholds depend on
- Iron pills, multivitamins with iron or an iron-rich meal shortly before the draw can raise the result.
- Infection and inflammation lower serum iron and so lower the percentage.
- Labcorp asks that the sample be drawn before iron treatment and that iron testing wait at least four days after a blood transfusion.
- Gross hemolysis and EDTA plasma can give wrong iron results, which carry through to the percentage.
- Some labs calculate it from iron and TIBC, while others use an estimate based on measured transferrin, so numbers can differ slightly.
Morning. Because the result is built from serum iron, it varies through the day. Changes within hours of iron intake because it is built from serum iron, so one result is a snapshot rather than a long-term measure.
When to talk to a clinician
Talk with a clinician soon if your transferrin saturation is 45% or higher on a repeat sample, especially with a high ferritin, joint pain, unusual tiredness or liver tests outside the range. A saturation below about 20% along with tiredness, shortness of breath or a low blood count is also worth discussing. If you or a child may have swallowed iron pills, call your local emergency number or poison control right away.
Questions you could ask
- How should I read my iron, TIBC, transferrin saturation and ferritin together?
- Could a recent iron pill or meal explain this?
- Should we repeat it on a fasting morning sample?
- Should we check ferritin and liver tests alongside it?
- Does this fit with low iron, or could inflammation be involved?
- Should we look at ferritin and my blood count together?
Questions people ask
My transferrin saturation is high but my ferritin is normal. Is that a problem?
It can be a one-off. Serum iron, which this number is built from, jumps after iron pills or an iron-rich meal. A high value that is confirmed on a repeat fasting sample is worth discussing, because Labcorp notes that saturation can rise before ferritin does in inherited iron overload. Your clinician can put it in context.
What is the difference between transferrin saturation and ferritin?
Ferritin shows how much iron you have in storage. Transferrin saturation shows how much iron is in transit in the blood right now. They answer different questions, so clinicians often read them together.
Why do guidelines mention 20% and 45%?
They are decision points used in guidelines, not diagnoses. Below about 20% is used in several guidelines to point to low available iron, including in kidney disease and heart failure. About 45% is a common level for looking further for iron overload. Your lab's own range, which for Labcorp is 15–55%, is a separate matter.
Do I need to fast before the test?
Many labs ask for a morning, fasting sample because the number depends on serum iron. The AASLD guideline says fasting is no longer absolutely necessary for screening, but it is reasonable to confirm a high result with a second sample, possibly a fasting one. Follow your lab's instructions.
Show the science and sources
For clinicians and researchers
TSAT = serum iron ÷ TIBC × 100, so it inherits the diurnal and pre-analytical variability of serum iron. Some labs instead divide iron by a TIBC estimated from measured transferrin, which gives slightly different results. Labcorp reports 15–55% and ARUP 20–50%; MedlinePlus lists 20–50% for men and 15–45% for women. For iron overload, the AASLD (2011) guideline notes that a 45% cutoff is often chosen for its high sensitivity for C282Y homozygotes, but it has lower specificity and also flags minor secondary iron overload and some heterozygotes. In patients with suggestive symptoms, findings or family history, it advises testing HFE when TS is ≥45% or ferritin is above the upper limit, and confirming a raised TS with a second sample, which can reasonably be a fasting one. EASL (2022) uses TSAT >45% with ferritin >200 µg/L in women, and TSAT >50% with ferritin >300 µg/L in men and postmenopausal women, as provisional iron overload in C282Y homozygotes. On the low side, BSG (2021) treats TSAT <20% as indicating iron restriction and defines absolute iron deficiency in CKD as TSAT ≤20% with ferritin ≤100 µg/L (≤200 in hemodialysis). KDIGO (2012) suggests an iron trial in anemic adults with CKD when TSAT is ≤30% and ferritin is ≤500 ng/mL. In heart failure, BSG describes iron deficiency as ferritin <100 µg/L and/or TSAT <20%.
LOINC 2502-3 (primary), 14801-5. Specimen: calculated.
Sources
- Iron and Total Iron-binding Capacity (TIBC) (test 001321), Labcorp
- Iron and TIBC sample report (test 001321), Labcorp
- Pediatric Testing Reference Ranges, Labcorp (2022)
- Iron and Iron Binding Capacity (test 0020420), ARUP Laboratories
- Total iron binding capacity, MedlinePlus Medical Encyclopedia (NIH)
- British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults, Gut (2021)
- KDIGO Clinical Practice Guideline for Anemia in Chronic Kidney Disease, Kidney International Supplements (2012)
- Diagnosis and management of hemochromatosis: 2011 practice guideline by the American Association for the Study of Liver Diseases, Hepatology (2011)
- EASL Clinical Practice Guidelines on haemochromatosis, Journal of Hepatology (2022)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.