Expected Hemoglobin in Iron Deficiency with Ferritin 8 µg/L
A ferritin of 8 µg/L indicates severe absolute iron deficiency with depleted iron stores, and the hemoglobin level can range from normal (non-anemic iron deficiency) down to profoundly low values (severe iron deficiency anemia), typically between 6–12 g/dL depending on the duration and severity of iron depletion. 1, 2
Understanding the Relationship Between Ferritin and Hemoglobin
Ferritin 8 µg/L is far below the diagnostic threshold of <15 µg/L, which has 99% specificity for absolute iron deficiency, confirming complete depletion of body iron stores 1, 2.
Iron deficiency progresses through stages: Stage 1 shows depleted iron stores (low ferritin) but normal hemoglobin; Stage 2 demonstrates iron-deficient erythropoiesis with falling hemoglobin; Stage 3 manifests as overt iron deficiency anemia with microcytic, hypochromic red cells 1, 2.
With ferritin as low as 8 µg/L, the patient has likely progressed beyond Stage 1, meaning some degree of anemia is probable, though the exact hemoglobin depends on how long iron stores have been depleted and the rate of ongoing blood loss 1, 2.
Expected Hemoglobin Range
In clinical practice, ferritin values of 8–10 µg/L typically correlate with hemoglobin levels in the range of 6–10 g/dL in adults, representing moderate to severe iron deficiency anemia 3, 4, 5.
Functional assessment studies demonstrate that iron-deficient erythropoiesis begins when ferritin reaches approximately 10 µg/L, meaning hemoglobin production is already impaired at this threshold 3.
In one prospective study of female patients with iron deficiency anemia and ferritin 10.2 ± 0.23 ng/dL, the mean baseline hemoglobin was 8.05 ± 0.89 g/dL, illustrating the typical severity of anemia at this ferritin level 4.
However, some patients may maintain hemoglobin in the 10–12 g/dL range despite ferritin of 8 µg/L if iron deficiency is relatively recent or if compensatory mechanisms (increased erythropoietin production) are still effective 1, 5.
Critical Factors That Determine Hemoglobin Level
Duration of iron deficiency: Chronic, long-standing deficiency allows hemoglobin to fall progressively lower, whereas acute iron loss may show less severe anemia initially 1, 5.
Rate of ongoing blood loss: Active gastrointestinal bleeding or heavy menstrual bleeding will drive hemoglobin lower despite compensatory erythropoiesis 1, 5.
Presence of inflammation or chronic disease: Concurrent inflammatory conditions (inflammatory bowel disease, chronic kidney disease, malignancy) can suppress erythropoiesis and worsen anemia beyond what ferritin alone would predict 1.
Bone marrow response capacity: Younger patients with healthy marrow may maintain higher hemoglobin longer, whereas elderly patients or those with marrow disease may develop more severe anemia at the same ferritin level 6.
Expected Red Blood Cell Indices
Mean corpuscular volume (MCV) will typically be low (microcytic anemia), often <80 fL, reflecting iron-restricted hemoglobin synthesis 1, 2.
Mean cell hemoglobin (MCH) will be reduced (hypochromic red cells), and red cell distribution width (RDW) will be elevated, indicating a mixed population of normal and iron-deficient red cells 1, 2.
Transferrin saturation (TSAT) will be markedly reduced, typically <10–16%, confirming insufficient iron delivery to the bone marrow for red blood cell production 1, 2.
Clinical Implications
Patients can survive with ferritin as low as 1–8 µg/L because the body prioritizes iron delivery to essential organs and red blood cell production, even when stores are exhausted, though symptoms of fatigue, weakness, and reduced exercise tolerance are universal 2.
The absence of anemia does not exclude clinically significant iron deficiency: Non-anemic iron deficiency (ferritin <15 µg/L with normal hemoglobin) still causes fatigue, reduced aerobic performance, and impaired quality of life 1, 2.
With ferritin 8 µg/L, immediate oral iron supplementation (ferrous sulfate 65 mg elemental iron daily or alternate-day dosing) should be initiated without waiting for further testing, and hemoglobin is expected to rise by ≥10 g/L within 2 weeks if iron deficiency is the sole cause 2, 4.
Concurrent investigation for the source of iron loss is mandatory: Screen for celiac disease (tissue transglutaminase antibodies), test for Helicobacter pylori, and consider bidirectional endoscopy in men, postmenopausal women, or those with gastrointestinal symptoms or family history of colorectal cancer 1, 2.
Common Pitfalls
Do not assume hemoglobin will be profoundly low just because ferritin is 8 µg/L: Some patients maintain hemoglobin in the 10–12 g/dL range if iron deficiency is recent or compensatory mechanisms are intact 1, 5.
Do not delay treatment while awaiting endoscopic evaluation: Start oral iron immediately, as response to therapy (hemoglobin rise ≥10 g/L in 2 weeks) helps confirm the diagnosis and improves symptoms rapidly 2, 4.
Do not overlook celiac disease, which accounts for 3–5% of iron deficiency cases and can cause treatment failure if not identified and managed 1, 2.