What is the likely diagnosis and recommended evaluation and treatment for an adult with serum iron 47 µg/dL, total iron‑binding capacity 394 µg/dL, transferrin saturation 12 % and ferritin 11 ng/mL?

Absolute Iron Deficiency Requiring Immediate Treatment and Investigation

This patient has severe absolute iron deficiency (ferritin 11 ng/mL, transferrin saturation 12%) that requires immediate oral iron supplementation and urgent investigation to identify the source of iron loss. 1, 2

Diagnostic Interpretation

Your laboratory results confirm absolute iron deficiency through multiple parameters:

• Ferritin 11 ng/mL is far below the diagnostic threshold of <15 ng/mL, which has 99% specificity for absolute iron deficiency 2
• Transferrin saturation 12% falls well below the critical threshold of 16–20%, indicating insufficient iron available for red blood cell production 2, 3
• Elevated TIBC 394 µg/dL reflects the body's compensatory attempt to capture more circulating iron when stores are depleted 2
• Low serum iron 47 µg/dL combined with the above parameters confirms impaired iron delivery to bone marrow for hemoglobin synthesis 2

This pattern represents Stage 1–2 iron deficiency where iron stores are severely depleted, though you may not yet have developed anemia (hemoglobin can remain normal initially). 2

Immediate Treatment Protocol

Start oral iron supplementation today—do not wait for investigation results:

• Ferrous sulfate 65 mg elemental iron daily (or ferrous bisglycinate/fumarate equivalent) 2, 4
• Alternate-day dosing (60 mg every other day) improves absorption by 30–50% and reduces gastrointestinal side effects compared to daily dosing 2
• Take on an empty stomach for optimal absorption; if nausea or constipation occurs, take with meals or switch to alternate-day dosing 2
• Expected response: Hemoglobin should rise by ≥10 g/L within 2 weeks if this is pure iron deficiency 2, 4

Mandatory Investigation for Source of Iron Loss

Your age, sex, and clinical context determine the investigation pathway:

For Adult Men and Postmenopausal Women

Urgent bidirectional endoscopy (gastroscopy + colonoscopy) is mandatory because gastrointestinal malignancy can present solely as iron deficiency without other symptoms. 1, 4

• Upper GI endoscopy identifies a cause in 30–50% of patients 4
• Dual pathology (both upper and lower GI lesions) occurs in 10–15% of cases 4
• Screen for celiac disease with tissue transglutaminase IgA antibody plus total IgA level—celiac disease accounts for 3–5% of iron deficiency cases and causes treatment failure if missed 2, 4
• Test for Helicobacter pylori (stool antigen or urea breath test) because it impairs iron absorption 2
• Perform urinalysis to exclude renal-tract bleeding 4

For Premenopausal Women

GI investigation is conditional rather than mandatory if you are young with heavy menstrual bleeding and no gastrointestinal symptoms. 2

Reserve bidirectional endoscopy for:

• Age ≥50 years (higher malignancy risk) 2, 4
• Gastrointestinal symptoms (abdominal pain, altered bowel habits, visible blood in stool) 2, 4
• Positive celiac or H. pylori testing requiring confirmation 2
• Failure to respond to adequate oral iron after 8–10 weeks 2, 4
• Strong family history of colorectal cancer 2

Still perform non-invasive screening:

• Celiac disease serologies (tissue transglutaminase IgA + total IgA) 2, 4
• H. pylori testing (stool antigen or urea breath test) 2
• Assess menstrual blood loss history—the most common cause in premenopausal women 2

Follow-Up and Monitoring

• Repeat CBC and ferritin at 8–10 weeks to assess response to treatment 2
• Target ferritin >100 ng/mL to fully restore iron stores and prevent recurrence 2
• If hemoglobin does not rise after 4 weeks of oral iron, consider malabsorption (celiac disease, inflammatory bowel disease), ongoing blood loss, or need for intravenous iron 2
• Do not test iron parameters within 4 weeks of starting treatment if you receive IV iron, as circulating iron interferes with assays 3

Indications for Intravenous Iron

Switch to intravenous ferric carboxymaltose (15 mg/kg, maximum 1000 mg per dose) if: 2

• Oral iron intolerance (severe nausea, constipation, diarrhea)
• Malabsorption confirmed (celiac disease, inflammatory bowel disease, post-bariatric surgery)
• Ongoing blood loss exceeding oral replacement capacity
• Failure to respond to adequate oral iron after 8–10 weeks
• Chronic inflammatory conditions (chronic kidney disease, heart failure, cancer)

Critical Pitfalls to Avoid

• Do not assume menstrual bleeding alone explains iron deficiency without first excluding GI pathology—this delays diagnosis of serious conditions like malignancy 4
• Do not overlook celiac disease screening—its 3–5% prevalence in iron deficiency cases leads to treatment failure if missed 2, 4
• Do not stop iron therapy when hemoglobin normalizes—continue until ferritin reaches ≥100 ng/mL to prevent rapid recurrence 2
• Do not delay iron supplementation while awaiting investigations unless colonoscopy can be performed within days—early treatment improves symptoms and does not compromise diagnostic accuracy 4

Long-Term Management

• For high-risk groups (menstruating females, vegetarians, athletes, regular blood donors), screen ferritin every 6–12 months 2
• Once ferritin normalizes, do not continue daily iron supplementation indefinitely—this is potentially harmful 2