Latent iron deficiency

Diagnosis

Diagnosis of latent iron deficiency relies on laboratory tests, with iron therapy suspended for 48 hours before testing to ensure valid results. A complete blood count and hemoglobin measurement are performed; hemoglobin levels are normal in LID, as anemia is absent. Serum iron, total iron-binding capacity, and serum ferritin are assessed. Normal serum iron ranges from 60 to 170 μg/dL, and normal total iron-binding capacity is 240 to 450 μg/dL for both sexes; total iron-binding capacity rises when iron deficiency is present.

Serum ferritin reflects body iron stores, with normal ranges of 20 to 200 ng/mL for men and 50 to 150 ng/mL for women; levels below 12 ng/mL are specific for iron deficiency, though inflammatory and neoplastic disorders such as hepatitis, leukemia, Hodgkin lymphoma, and gastrointestinal tract tumors can elevate ferritin. The most sensitive and specific criterion for iron-deficient erythropoiesis is depleted iron stores in the bone marrow, but bone marrow examination is rarely performed in practice.

LID corresponds to Stages 1 and 2 of iron deficiency, before anemia appears in Stage 3. Stage 1 involves loss of bone marrow iron stores with normal hemoglobin and serum iron; serum ferritin falls below 20 ng/mL, and increased iron absorption raises transferrin and iron-binding capacity. Stage 2 shows impaired erythropoiesis, with decreased serum iron below 50 μg/dL and transferrin saturation under 16%, despite elevated transferrin levels.

Treatment

No consensus exists on treating latent iron deficiency, but one approach mirrors that for iron-deficiency anemia: administering ferrous sulfate at 100 mg per day in two doses (with breakfast and dinner) for adults, or 3 mg per kg per day in two doses for children, over two to three months. The goal is to raise serum ferritin to between 30 and 100 ng/mL, as a clinical study found increased ferritin in those taking iron versus placebo; ferritin above 100 ng/mL has been linked to more infections. Alternatively, an iron-rich diet combined with ascorbic acid (vitamin C) from fruits like oranges and kiwifruits can enhance iron absorption two- to fivefold.

Epidemiology

The frequency of latent iron deficiency varies by country, diet, pregnancy, age, and gender. Reported rates include 11% among male athletes in Poland, 26% among female athletes in Poland, 27.5% among student nurses in India, and 14.7% among women of child-bearing age in Barcelona, Spain. In China, LID was found in 42.6% of pregnant women and 34.4% of premenopausal non-pregnant women across 15 provinces; among 9,118 children aged 7 months to 7 years from 31 provinces, the incidence was 32.5%. Subclassified by age, LID occurred in 44.7% of children under 1 year old, 35.9% of those aged 1 to 3 years, and 26.5% of those aged 4 to 7 years.