Diagnosis and Management of Iron Deficiency

Diagnostic Criteria

Transferrin saturation < 15 % defines absolute iron deficiency and has high sensitivity for the condition (National Comprehensive Cancer Network, NCCN) [1][3]4
Low serum iron concentration (e.g., ≈ 50 µg/dL) supports the diagnosis of iron deficiency (Clinical Nutrition) 5

Ferritin < 30 ng/mL confirms absolute iron deficiency when inflammation is absent (NCCN) [1][2]
Ferritin < 12–15 µg/L is diagnostic of iron deficiency regardless of inflammatory status (British Society of Gastroenterology guidelines) 6
In the presence of elevated inflammatory markers (e.g., CRP, ESR), a ferritin threshold < 100 µg/L should be used to diagnose iron deficiency (British Society of Gastroenterology) [3][4]

All patients with confirmed iron deficiency require investigation for the source to reduce morbidity and mortality (British Society of Gastroenterology) [6][8]
Bidirectional endoscopy (upper + lower GI) is recommended unless a clear non‑gastrointestinal source of blood loss is identified (British Society of Gastroenterology) [6][8]
Upper endoscopy with duodenal biopsies should be performed to exclude celiac disease, which accounts for ~2–3 % of iron‑deficiency anemia cases (British Society of Gastroenterology) [6][7]
Colonoscopy is indicated to rule out colorectal cancer, polyps, angiodysplasia, and inflammatory bowel disease (British Society of Gastroenterology) [6][8]
Dual pathology occurs in ≈ 10 % of cases; therefore both upper and lower evaluations are advised even if one lesion is found (British Society of Gastroenterology) 6
A detailed menstrual history should be obtained in premenopausal individuals (Clinical Gastroenterology and Hepatology) 7
NSAID or aspirin use should be discontinued when possible to avoid gastrointestinal blood loss (British Society of Gastroenterology) 6
Assessment of dietary iron intake is part of the work‑up (Clinical Gastroenterology and Hepatology) 7
Testing for Helicobacter pylori infection is recommended as a potential reversible cause (Clinical Gastroenterology and Hepatology) 7

Begin iron supplementation concurrently with diagnostic evaluation (NCCN) [1][5]7

Prescribe 100–200 mg elemental iron daily in divided doses (Clinical Nutrition) 5
Ferrous sulfate, ferrous fumarate, or ferrous gluconate are appropriate formulations (Clinical Gastroenterology and Hepatology) 7
Administer on an empty stomach if tolerated; otherwise with meals to improve gastrointestinal comfort (Clinical Gastroenterology and Hepatology) 7
Alternate‑day dosing may enhance absorption and reduce side‑effects (Clinical Nutrition) 5
Reassess hemoglobin and iron studies after ≈ 4 weeks of oral therapy (NCCN) 9

Switch to IV iron if oral therapy is intolerable or ineffective after ≈ 4 weeks (Clinical Nutrition; NCCN) [5][9]
IV iron is preferred in malabsorption states (e.g., celiac disease, inflammatory bowel disease, post‑bariatric surgery) (British Society of Gastroenterology; Clinical Gastroenterology and Hepatology) [8][7]
Use IV iron for rapid repletion when a swift correction is clinically required (Clinical Nutrition) 5
Chronic kidney disease, heart failure, and inflammatory bowel disease benefit from IV iron due to superior outcomes (British Society of Gastroenterology; American Society of Hematology) [8][10]

Repeat complete blood count and iron parameters 4–8 weeks after initiating therapy (American Society of Hematology) 10
Expect a hemoglobin rise of 1–2 g/dL within 4–8 weeks of appropriate treatment (American Society of Hematology) 10
Target ferritin ≥ 50 ng/mL in the absence of inflammation (American Society of Hematology) 10
Do not measure iron studies within 4 weeks of IV iron administration because the infusion interferes with assay accuracy (American Society of Hematology) 10

Do not skip ferritin measurement; it remains the most powerful single test for iron deficiency (British Society of Gastroenterology) 6
Do not attribute iron deficiency solely to dietary insufficiency without GI investigation; occult gastrointestinal pathology is common (British Society of Gastroenterology) 6
Do not overlook inflammation; adjust ferritin thresholds accordingly (British Society of Gastroenterology) [3][4]
Do not prescribe iron supplementation when ferritin is normal or elevated without confirming true deficiency, as this may cause harm (Clinical Nutrition) 5