Interpretation: Severe Absolute Iron Deficiency with Early Microcytic Anemia
This 36-year-old woman has severe absolute iron deficiency with early microcytic anemia, confirmed by a ferritin of 8 ng/mL (far below the diagnostic threshold of <15 ng/mL, which has 99% specificity for iron deficiency) and a transferrin saturation of 4.4% (calculated as [22 ÷ 496] × 100), well below the critical threshold of 16%. 1
Laboratory Pattern Analysis
Iron Studies:
- Ferritin 8 ng/mL: Definitively confirms depleted iron stores; this value is approximately 1 μg/L of serum ferritin equals 10 mg of stored iron, indicating near-complete depletion of body iron reserves 2, 1
- Transferrin saturation 4.4%: Severely reduced iron availability for erythropoiesis; values <16% confirm iron deficiency even when other parameters are equivocal 2, 1
- Elevated TIBC (496 mg/dL) and UIBC (474 mg/dL): The body is attempting to capture more circulating iron by increasing transferrin production, a compensatory response to depleted stores 2, 3
- Low serum iron (22 μg/dL): Reflects insufficient iron in circulation for immediate hemoglobin synthesis 2, 3
Red Blood Cell Parameters:
- Hemoglobin 11.4 g/dL: Below the normal threshold of 12 g/dL for nonpregnant women, confirming anemia 4
- MCV 79 fL, MCH 24.2 pg, MCHC 30.5 g/dL: All reduced, indicating microcytic hypochromic anemia characteristic of iron-restricted erythropoiesis 2, 3, 5
- RBC 4.72 million/μL: Relatively preserved count despite anemia, reflecting the body's attempt to maintain oxygen-carrying capacity by producing more (albeit smaller and paler) red cells 5
This pattern represents Stage 2 iron deficiency where MCV and MCH have declined, hemoglobin is subnormal but above 9 g/dL, and transferrin saturation is far below 16%. 5
Immediate Management Protocol
1. Initiate Oral Iron Supplementation Immediately:
- Start ferrous sulfate 65 mg elemental iron daily, or 60 mg every other day (alternate-day dosing improves absorption by 30-50% and reduces gastrointestinal side effects) 1
- Take on an empty stomach for optimal absorption, or with meals if gastrointestinal symptoms develop 1
- Expected response: hemoglobin should rise by ≥10 g/L within 2 weeks of starting therapy 1
2. Investigate the Source of Iron Loss:
For a 36-year-old premenopausal woman, the diagnostic algorithm should proceed as follows:
- Assess menstrual history: Heavy or prolonged menstrual bleeding (menometrorrhagia) is the most common cause of iron deficiency in this population 6, 4
- Screen for celiac disease: Obtain tissue transglutaminase IgA antibodies; celiac disease accounts for 3-5% of iron deficiency cases and causes treatment failure if missed 1
- Test for Helicobacter pylori: Use stool antigen or urea breath test; the organism impairs iron absorption 1
Reserve bidirectional endoscopy for:
- Age ≥50 years (higher malignancy risk)
- Gastrointestinal symptoms (abdominal pain, altered bowel habits, visible blood in stool)
- Positive celiac or H. pylori testing requiring confirmation
- Failure to respond to adequate oral iron after 8-10 weeks
- Strong family history of colorectal cancer 1
In young, asymptomatic premenopausal women with heavy menses and no gastrointestinal symptoms, empiric oral iron supplementation without immediate endoscopy is appropriate. 1
3. Consider Intravenous Iron if:
- Oral iron intolerance develops (constipation, nausea, diarrhea)
- Malabsorption is documented (celiac disease, inflammatory bowel disease)
- Ongoing blood loss exceeds oral replacement capacity
- Pregnancy in second/third trimester 1
Follow-Up and Monitoring
- Repeat CBC and ferritin at 8-10 weeks to assess response to treatment 1
- Target ferritin >100 ng/mL to fully replenish iron stores and prevent recurrence 1
- For recurrent low ferritin (common in menstruating females), schedule ferritin screening every 6-12 months 1
- Do not continue daily iron supplementation once ferritin normalizes, as this is potentially harmful 1
Critical Pitfalls to Avoid
- Do not assume normal hemoglobin excludes significant iron deficiency: This patient's hemoglobin of 11.4 g/dL is only mildly reduced, yet her ferritin of 8 ng/mL indicates severe depletion of iron stores 1, 5
- Do not overlook celiac disease screening: Its 3-5% prevalence in iron deficiency cases can lead to treatment failure if not identified 1
- Do not perform extensive gastrointestinal investigation in young, asymptomatic premenopausal women with heavy menses: The yield is extremely low (0-6.5%) unless red flags are present 1
- Do not misinterpret this as anemia of chronic disease: The elevated TIBC (496 mg/dL) definitively excludes anemia of chronic disease, which presents with low or normal TIBC 3, 7