Interpretation and Management of Slightly Elevated Serum Iron with Low‑Normal Ferritin

Laboratory Variability and Basic Principles

Serum iron exhibits marked day‑to‑day and diurnal variation, increasing after meals, peaking in the morning, and falling at night, making it an unreliable solitary marker of iron status. 1, 2
Ferritin is the most specific laboratory indicator of depleted iron stores when inflammation is absent; low‑normal ferritin (≈15–30 µg/L) suggests marginal iron reserves. 1, 3, 4
Within‑individual variability is considerably greater for serum iron than for ferritin, so ferritin provides a more stable assessment of true iron status. 1, 2

Ferritin < 15 µg/L identifies absolute iron deficiency with 98–100 % specificity. 1, 6
Ferritin 15–30 µg/L indicates likely depleted iron stores. 4
Transferrin saturation < 16 % denotes functional iron deficiency even when ferritin appears normal. 7, 8

Ferritin threshold must be raised; ferritin < 30 µg/L still points to iron deficiency despite inflammatory elevation of ferritin. 7, 8
Ferritin 30–100 µg/L together with transferrin saturation < 16 % suggests a mixed picture of true iron deficiency plus anemia of chronic disease. 7, 8, 9
Ferritin > 100 µg/L with transferrin saturation < 16 % is characteristic of anemia of chronic disease alone. 7, 8

Transferrin saturation = (serum iron ÷ total iron‑binding capacity) × 100 %. 1, 3, 2
A saturation < 16 % is a sensitive marker of iron deficiency, especially in the presence of inflammation. 7, 8, 9

Soluble transferrin receptor (sTfR) rises in iron deficiency but remains normal or low in anemia of chronic disease; the sTfR / log₁₀ ferritin ratio improves discrimination in chronic inflammatory conditions. 7, 8, 4
Reticulocyte hemoglobin content provides a more precise estimate of iron availability during inflammation. 7
Mean corpuscular hemoglobin (MCH) is more sensitive than mean corpuscular volume (MCV) for detecting iron deficiency and is less affected by analyzer variability. 4

Initiate iron therapy once iron deficiency is confirmed, even if anemia is not yet present. 8, 10

Ferrous salts (ferrous sulfate, fumarate, gluconate) are appropriate initial agents unless malabsorption, intolerance, or severe deficiency contraindicates oral therapy. 8, 10
Oral iron is best absorbed on an empty stomach, though some patients tolerate it better with food; co‑administration of ~500 mg vitamin C enhances absorption. 10

Consider IV iron for severe deficiency, documented malabsorption, or when oral iron is poorly tolerated. 8, 10

Do not rely on serum iron alone because of its high variability related to meals, diurnal rhythm, and inflammatory status. 1, 2
Do not assume normal iron stores based solely on low‑normal ferritin; always calculate transferrin saturation for a more accurate assessment. 7, 8
In inflammatory conditions, ferritin may be falsely elevated; always assess inflammatory markers (CRP, ESR) to avoid missing underlying iron deficiency. 7, 3, 5