Type the TIBC (total iron binding capacity) from your iron panel. You see it against the adult ranges MedlinePlus and Mayo Clinic Laboratories print, and — if you add the serum iron from the same report — your transferrin saturation by the lab’s own formula. Ferritin, your lab’s own range and your doctor have the last word.
320 mcg/dL is
Inside both adult ranges 320 mcg/dL = 57.3 µmol/L
320 mcg/dL: inside the 149–492 mcg/dL MedlinePlus prints for women, and inside the 250–400 mcg/dL Mayo Clinic Laboratories prints for adults.
That is inside both adult ranges. The range on your own lab report — and your ferritin — are what your doctor reads it against.
Mayo Clinic Laboratories: “However, serum ferritin is a much more sensitive and reliable test for demonstration of iron deficiency.” Check a ferritin result.
What moves the number, in the sources’ words
- Normal value ranges may vary slightly among different laboratories.
| Source | TIBC | Iron | Saturation |
|---|---|---|---|
| MedlinePlus, women | 149–492 | 37–145 | 15–45% |
| MedlinePlus, men | 171–505 | 59–158 | 20–50% |
| Mayo, women | 250–400 | 35–145 | 14–50% |
| Mayo, men | 250–400 | 50–150 | 14–50% |
This is not medical advice and it does not diagnose anything. It shows where a number sits against published ranges; what your result means for you depends on your lab, your ferritin, your other results, your history and your doctor.
MedlinePlus prints a normal TIBC of 149 to 492 mcg/dL for women and 171 to 505 mcg/dL for men; Mayo Clinic Laboratories prints 250 to 400 mcg/dL for adults. A result between the two is inside one range and outside the other. MedlinePlus: “TIBC is usually higher than normal when the body’s iron supplies are low.” Ferritin is the better test for that.
How to use it
Type the TIBC line from your iron panel, say whether it is printed in mcg/dL (the same number as µg/dL) or µmol/L, and pick the ranges for women or men. You see where it sits against each adult range a source prints, the two side by side, and what the sources say moves it. If the same report prints a serum iron, type it too (in the same unit): you see where it sits, and your transferrin saturation by the formula Mayo Clinic Laboratories prints — “Percent saturation = (Iron/TIBC) x 100”. It does not diagnose anything: it places a number and quotes the sources.
What TIBC measures
MedlinePlus: “Total iron binding capacity (TIBC) is a blood test to see if you have too much or too little iron in your blood. Iron moves through the blood attached to a protein called transferrin. This test helps your health care provider know how well that protein can carry iron in your blood.” Its iron-tests page describes it as “Total iron-binding capacity (TIBC), which measures how well iron attaches to transferrin and other proteins in the blood”. Mayo Clinic Laboratories calculates it from transferrin: “Total iron-binding capacity (TIBC) is estimated from the transferrin concentration using the molecular weight of transferrin, accounting for each transferrin molecule that can bind 2 atoms of iron.” Its formula is “Total iron-binding capacity (TIBC) = Transferrin x 1.18”. And it says what the body does with transferrin: “The circulating concentration increases in response to iron deficiency and decreases in response to iron overload.”
The ranges the sources print
| Source | TIBC | Serum iron | Saturation |
|---|---|---|---|
| MedlinePlus, women | 149–492 mcg/dL (26.7–88.0 µmol/L) | 37–145 mcg/dL (6.6–25.9 µmol/L) | 15–45% |
| MedlinePlus, men | 171–505 mcg/dL (30.6–90.3 µmol/L) | 59–158 mcg/dL (10.6–28.3 µmol/L) | 20–50% |
| Mayo Clinic Laboratories, women | 250–400 mcg/dL (44.8–71.6 µmol/L) | 35–145 mcg/dL (6.3–26.0 µmol/L) | 14–50% |
| Mayo Clinic Laboratories, men | 250–400 mcg/dL (44.8–71.6 µmol/L) | 50–150 mcg/dL (9.0–26.9 µmol/L) | 14–50% |
MedlinePlus prints “Total iron binding capacity (TIBC): Males: 171 to 505 mcg/dL (30.6 to 90.3 micromol/L); Females: 149 to 492 mcg/dL (26.7 to 88.0 micromol/L)” and says “The numbers above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories.” Mayo Clinic Laboratories (test SFEC) prints “IRON Males: 50-150 mcg/dL Females: 35-145 mcg/dL TOTAL IRON-BINDING CAPACITY 250-400 mcg/dL PERCENT SATURATION 14-50%”, in mcg/dL only; its µmol/L figures above are ours, by iron’s atomic weight (1 µmol/L = 5.5845 mcg/dL), and MedlinePlus’s own printed pairs agree with that factor to within 0.15. This checker is for adults.
Transferrin saturation: the number beside it
Mayo Clinic Laboratories calculates “Percent saturation = (Iron/TIBC) x 100” — the share of the transferrin’s iron seats that are filled. MedlinePlus calls it iron saturation; your report may say “% saturation” or “TSAT”. Mayo: “Transferrin is generally only 25% to 30% saturated with iron.” “Iron concentration and percent saturation decrease with iron deficiency and increase when iron is in excess.” It also prints the lines doctors screen with: “Percent saturation less than 16% is generally used to screen for iron deficiency, but a threshold of 20% is used in the presence of inflammation.” “Percent saturation often exceeds 45% in hereditary hemochromatosis and 90% in advanced iron overload states.” This checker shows the saturation to one decimal; your lab may round it to a whole percent.
What raises or lowers it
MedlinePlus: “TIBC is usually higher than normal when the body’s iron supplies are low.” It names Iron deficiency anemia and Pregnancy (late). “Lower-than-normal TIBC may mean:” Anemia due to red blood cells being destroyed too quickly (hemolytic anemia); Lower-than-normal level of protein in the blood (hypoproteinemia); Inflammation; Liver disease, such as cirrhosis; Malnutrition; Decrease in red blood cells due to the intestines not properly absorbing vitamin B12 (pernicious anemia); Sickle cell anemia. “Certain medicines may affect the result of this test.” It names Adrenocorticotropic hormone (ACTH), Birth control pills and Fluorides — and “Do not stop any medicine before talking to your provider.” Its iron-tests page adds: “If your iron test results are not normal, it does not necessarily mean you have a medical condition that needs treatment.”
Ferritin comes first
For the question most readers of this site bring — is my iron low? — Mayo Clinic Laboratories is plain: “However, serum ferritin is a much more sensitive and reliable test for demonstration of iron deficiency.” Of the iron panel itself: “This test should not be used as the primary test for iron deficiency.” Read TIBC and saturation beside a ferritin result, not instead of one: the Ferritin Level Checker places it against the NIH’s and the WHO’s lines.
Before the blood draw, if you take iron
Mayo Clinic Laboratories’ patient preparation for this panel: “For 24 hours before collection, patient should not take iron-containing supplements.” MedlinePlus: “You should not eat or drink for 8 hours before the test.” Serum iron moves through the day — MedlinePlus: “The amount of iron in your blood varies throughout the day and may be higher in the morning.” Mayo: “The intraindividual day-to-day variation of iron and iron saturation is approximately 25% to 30%.” and “minimizing influence of these effects can be accomplished by collecting during the morning after an overnight fast.” Ask the person who ordered the test before changing anything you take.
Worked examples
- 320 mcg/dL, woman (the page’s example): inside both adult ranges.
- 450 mcg/dL, woman: inside MedlinePlus’s 149–492, above Mayo’s 250–400 — the sources disagree, and the answer says so. With a serum iron of 60, the saturation is 60 ÷ 450 × 100 = 13.3%: under both sources’ saturation ranges.
- 200 mcg/dL, man: inside MedlinePlus’s 171–505, under Mayo’s 250. With a serum iron of 150, the saturation is 75%: above both.
- 62 µmol/L, man: inside MedlinePlus’s 30.6–90.3 µmol/L and inside Mayo’s 250–400 mcg/dL (44.8–71.6 µmol/L).
Common mistakes
- Reading TIBC as an iron level. It is how much iron the blood’s transferrin could carry; the serum iron is how much it carries now. A high TIBC goes with LOW iron supplies.
- Mixing units in the saturation. Iron and TIBC must be in the same unit; the units cancel in Mayo’s formula.
- Taking iron the morning of the test. Mayo asks for 24 hours without iron-containing supplements.
- Treating one source’s range as the only one. MedlinePlus and Mayo Clinic Laboratories print very different TIBC ranges; your lab prints its own.
- Skipping the ferritin. Mayo calls ferritin the more sensitive and reliable test for iron deficiency.
Frequently asked questions
What is a TIBC blood test?
MedlinePlus: “Total iron binding capacity (TIBC) is a blood test to see if you have too much or too little iron in your blood.” It shows how well transferrin, the protein that carries iron in the blood, can carry it; Mayo Clinic Laboratories calculates it from the transferrin.
What is a normal total iron binding capacity?
MedlinePlus prints 149 to 492 mcg/dL for women and 171 to 505 mcg/dL for men; Mayo Clinic Laboratories prints 250 to 400 mcg/dL for adults. Your lab’s printed range is the one your doctor uses.
What does a high TIBC blood test mean?
MedlinePlus: “TIBC is usually higher than normal when the body’s iron supplies are low.” It names iron deficiency anemia and late pregnancy. Mayo says transferrin, from which it calculates TIBC, “increases in response to iron deficiency”. Ferritin is the test that settles it, with your doctor.
What does a low TIBC mean?
MedlinePlus lists hemolytic anemia, a low level of protein in the blood (hypoproteinemia), inflammation, liver disease such as cirrhosis, malnutrition, pernicious anemia and sickle cell anemia. It also says an abnormal iron test “does not necessarily mean you have a medical condition that needs treatment”.
How is transferrin saturation calculated from TIBC?
Mayo Clinic Laboratories prints it: “Percent saturation = (Iron/TIBC) x 100”. A serum iron of 75 and a TIBC of 300 give 25%. Both numbers must be in the same unit.
Should I stop iron before a TIBC test?
Mayo Clinic Laboratories’ preparation for its iron panel says: “For 24 hours before collection, patient should not take iron-containing supplements.” Ask whoever ordered your test; MedlinePlus also asks for 8 hours without food or drink.
Is TIBC the same as transferrin?
Not the same number, but tied to it: Mayo Clinic Laboratories calculates “Total iron-binding capacity (TIBC) = Transferrin x 1.18”, because each transferrin molecule can bind two atoms of iron.
More iron and blood-count checkers: the Ferritin Level Checker, the Hemoglobin Level Checker, the Reticulocyte Count Checker and the Iron Tablet Timing Planner.
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This is not medical advice, and nothing here diagnoses or treats anything. It shows where a number sits against published adult ranges and quotes what the sources say moves it; your lab’s own range, your ferritin, your other results and your doctor decide what it means. Some links on this site are affiliate links: I buy what I review at full price, and a commission never changes a verdict.