What are the normal reference ranges for iron studies (serum iron, ferritin, total iron‑binding capacity, transferrin saturation) in healthy adults?

Normal Iron Levels in Healthy Adults

In healthy adults, normal serum iron ranges from 50–175 µg/dL, total iron-binding capacity (TIBC) from 250–370 µg/dL (45–66 µmol/L), transferrin saturation from 20–50%, and serum ferritin from 20–250 µg/L in men and 20–200 µg/L in women. 1, 2

Serum Iron

• Serum iron measures circulating iron bound to transferrin and typically ranges from 50–175 µg/dL in healthy adults. 1, 2
• This marker exhibits significant day-to-day variability and is influenced by recent meals, diurnal rhythms, and inflammatory states, limiting its standalone diagnostic utility. 1, 2
• Serum iron should not be used in isolation to assess iron status due to its poor reliability. 1

Total Iron-Binding Capacity (TIBC)

• TIBC reflects the iron-binding capacity of transferrin in serum and normally ranges from 250–370 µg/dL (45–66 µmol/L). 1, 2
• TIBC increases when serum iron and stored iron are low, representing the body's compensatory effort to capture circulating iron. 3
• TIBC equals the sum of serum iron plus unsaturated iron-binding capacity (UIBC). 3

Transferrin Saturation (TSAT)

• Transferrin saturation is calculated by dividing serum iron by TIBC and multiplying by 100, with a normal range of 20–50%. 1, 3, 2
• TSAT indicates the proportion of transferrin binding sites occupied by iron; low TSAT reflects a high proportion of vacant binding sites. 1, 3
• Values below 20% indicate iron-deficient erythropoiesis, while values below 16% are diagnostic for iron deficiency in adults. 3

Serum Ferritin

• Ferritin reference intervals in adults are 20–250 µg/L in men (assay-dependent range 24–336 µg/L) and 20–200 µg/L in women. 1, 2
• Under normal conditions, 1 µg/L of serum ferritin corresponds to approximately 10 mg of stored iron. 1
• Ferritin is the most specific indicator of iron stores, but it behaves as an acute-phase reactant and can be falsely elevated during inflammation, infection, or tissue damage. 1, 2

Critical Caveat on Ferritin Reference Ranges

• The commonly reported lower limit of normal (LLN) for ferritin—typically 8–11 µg/L in women and 22–25 µg/L in men—is not rooted in rigorous scientific evidence and contributes to structural underdiagnosis of iron deficiency. 4
• Studies establishing these reference intervals frequently failed to exclude individuals at risk for iron deficiency and did not adhere to reference interval establishment standards. 4
• A ferritin concentration below 30 µg/L has high specificity and sensitivity for diagnosing iron deficiency in adults when inflammation is absent. 3, 2, 4
• In the presence of inflammation, ferritin values up to 100 µg/L may still be compatible with true iron deficiency. 3, 2

Hemoglobin

• Normal hemoglobin ranges are 13.5–17.5 g/dL in men and 12.0–15.5 g/dL in women. 1, 2
• Hemoglobin reflects adequate oxygen-carrying capacity and decreases in iron-deficiency anemia. 1

Mean Corpuscular Volume (MCV)

• The normal MCV range is 80–100 fL. 1, 2
• MCV decreases in iron-deficiency anemia, but more than 50% of individuals with confirmed iron deficiency have a normal MCV, limiting its sensitivity (43–48%). 3

Serum Transferrin

• Normal transferrin concentration is 200–400 mg/dL. 1, 2
• Transferrin levels rise proportionally when iron demand increases, serving as an indicator of iron needs. 1

Optimal Diagnostic Approach

• Ferritin combined with transferrin saturation provides the most reliable assessment of iron status. 2
• Low ferritin (<30 µg/L in the absence of inflammation) together with low TSAT (<16%) unequivocally confirms absolute iron deficiency. 3, 2
• Normal serum iron and TIBC values do not exclude iron deficiency and must be interpreted alongside ferritin and TSAT. 3, 2
• Measuring C-reactive protein is essential to identify concurrent inflammation, as inflammation can falsely elevate ferritin and mask true iron deficiency. 3

Additional Markers

• Hepcidin (normal range 6.7–10.4 ng/mL) regulates iron efflux from enterocytes and may prove to be the most precise way to diagnose deficiency in inflammatory conditions, though it is not yet widely available. 1
• Soluble transferrin receptor (normal range 0.76–1.76 mg/L) reflects functional iron status and is not influenced by inflammation. 1
• Bone marrow iron staining remains the gold standard for diagnosing iron deficiency when results are unclear, showing no visible or only small iron particles in deficiency. 1