What is the most likely diagnosis and recommended management for a patient with low serum iron, low transferrin saturation, and low ferritin?

Absolute Iron Deficiency: Diagnosis Confirmed

This patient has absolute iron deficiency with depleted iron stores, confirmed by ferritin 23 ng/mL (below the 30 ng/mL threshold), transferrin saturation 13% (well below 16-20%), and serum iron 48 µg/dL. 1

Diagnostic Interpretation

Your laboratory pattern definitively establishes iron deficiency through three converging markers:

• Ferritin 23 ng/mL indicates depleted body iron stores, falling within the 15-30 ng/mL range that confirms low iron reserves requiring treatment 1
• Transferrin saturation 13% is critically below the 16% threshold (sensitivity marker for iron deficiency), demonstrating insufficient iron available for red blood cell production 1
• Serum iron 48 µg/dL reflects the low circulating iron that produces the reduced transferrin saturation 1

This triad—low ferritin, low TSAT, low serum iron—defines absolute iron deficiency where both storage iron (ferritin) and functional iron (TSAT) are depleted. 1

Immediate Management Protocol

Start Oral Iron Supplementation Now

Initiate ferrous sulfate 65 mg elemental iron daily (or 60-65 mg every other day) immediately without waiting for diagnostic workup completion. 1

• Alternate-day dosing improves absorption by 30-50% and reduces gastrointestinal side effects (constipation, nausea, diarrhea) 1, 2
• Take on an empty stomach for optimal absorption; switch to with-meals dosing only if intolerable side effects occur 1
• Expected response: hemoglobin should rise ≥10 g/L within 2 weeks of starting therapy 1

Mandatory Investigation for Blood Loss Source

The underlying cause must be identified because recurrent blood loss accounts for 94% of iron deficiency cases. 2

For adult men and postmenopausal women:

• Bidirectional endoscopy (upper GI gastroscopy + colonoscopy) is mandatory because iron deficiency may be the sole manifestation of gastrointestinal malignancy 1, 2

For premenopausal women:

• Assess menstrual blood loss history first (most common cause in this population) 1
• Screen for celiac disease with tissue transglutaminase IgA antibodies—present in 3-5% of iron deficiency cases and causes treatment failure if missed 1, 2
• Test for Helicobacter pylori (stool antigen or urea breath test) because it impairs iron absorption 1, 2
• Reserve bidirectional endoscopy for: age ≥50 years, GI symptoms (abdominal pain, altered bowel habits, visible blood), positive celiac or H. pylori testing, failure to respond to oral iron after 8-10 weeks, or strong family history of colorectal cancer 1

Follow-Up and Monitoring

• Recheck CBC and ferritin at 8-10 weeks to assess therapeutic response 1, 2
• Target ferritin >100 ng/mL to fully restore iron stores and prevent rapid recurrence 1
• Continue oral iron for 3 months after hemoglobin normalizes because absorbed iron is initially directed to red cell production; storage compartments refill only after hemoglobin corrects 1

Indications to Switch to Intravenous Iron

Transition to intravenous ferric carboxymaltose (15 mg/kg, maximum 1000 mg per dose) if any of the following apply: 1, 3

• Severe oral iron intolerance (marked nausea, constipation, diarrhea)
• Confirmed malabsorption (celiac disease, inflammatory bowel disease, post-bariatric surgery)
• Ongoing blood loss exceeding oral replacement capacity
• Lack of hemoglobin response after 8-10 weeks of adequate oral iron
• Chronic inflammatory conditions (chronic kidney disease, heart failure, cancer)

IV iron produces reticulocytosis within 3-5 days and yields a mean hemoglobin increase of approximately 8 g/L over 8 days, demonstrating superior efficacy in these populations. 1

Critical Pitfalls to Avoid

• Do not assume dietary iron alone will correct this deficiency—supplementation is mandatory because dietary intake cannot replenish depleted stores within a clinically acceptable timeframe 1
• Do not stop iron therapy once hemoglobin normalizes—an additional 3 months is required to achieve ferritin >100 ng/mL 1
• Do not overlook celiac disease screening (3-5% prevalence in iron deficiency)—missing this diagnosis leads to treatment failure 1, 2
• Do not delay endoscopic evaluation in high-risk patients (men, postmenopausal women, age ≥50, alarm symptoms)—GI malignancy can present solely with iron deficiency 1, 2

High-Risk Populations Requiring Ongoing Surveillance

For patients at risk of recurrent iron depletion (menstruating females, vegetarians, athletes, regular blood donors), schedule ferritin screening every 6-12 months to detect early depletion before anemia develops. 1