Iron Status Interpretation in a 33-Year-Old Active Female
These labs indicate early iron depletion (low iron stores) without anemia, characterized by a low transferrin saturation of 15% despite normal ferritin at 31 ng/mL, which warrants iron supplementation to prevent progression to iron deficiency anemia. 1
Understanding the Lab Values
Your patient's iron panel reveals:
- Transferrin saturation of 15% is definitively low (normal threshold >20%), indicating insufficient iron available for red blood cell production 2
- Ferritin of 31 ng/mL sits at the lower end of normal range for women (average 43 μg/L in US women), representing early depletion of iron stores 1
- Normal CBC confirms this is non-anemic iron deficiency (NAID), where iron stores are depleted but hemoglobin remains normal 2
Clinical Significance
The transferrin saturation is the most clinically important finding here. 3, 4
- A TSAT <20% is the most reliable indicator of true iron deficiency, more so than ferritin alone 3, 4
- Recent evidence demonstrates that low TSAT (not ferritin) predicts clinical outcomes and identifies patients who benefit from iron repletion 3, 4
- Ferritin of 31 ng/mL represents approximately 310 mg of stored iron (each 1 μg/L = ~10 mg stored iron), which is depleted but not yet critically low 1
Why This Matters in an Active Female
Premenopausal women are at high risk for iron depletion due to menstrual blood loss, and active individuals have increased iron demands. 2
- The combination of menstruation and athletic activity creates ongoing iron losses that exceed dietary intake 2
- Even without anemia, low iron stores can impair exercise capacity and cause fatigue 2
- A ferritin <45 μg/L in the context of low TSAT warrants consideration of iron supplementation 2
Recommended Management
Initiate oral iron supplementation now to replenish iron stores before anemia develops. 1
Iron Supplementation Protocol:
- Ferrous sulfate 200 mg three times daily is first-line therapy 1
- Continue treatment for three months after any symptoms resolve to fully replenish iron stores 1
- Recheck iron studies (ferritin and TSAT) after 3 months of therapy 1
When to Investigate Further:
In premenopausal women with NAID, gastrointestinal investigation is generally NOT warranted unless: 2
- GI symptoms are present (abdominal pain, change in bowel habits, blood in stool)
- Family history of GI malignancy or celiac disease
- Failure to respond to adequate oral iron supplementation
- Progressive worsening despite treatment
The low threshold for investigation applies primarily to men, postmenopausal women, or those with concerning symptoms 2
Important Caveats
Ferritin is an acute-phase reactant - if your patient has any concurrent inflammation, infection, or chronic disease, the ferritin of 31 ng/mL may actually mask more severe iron deficiency 2, 1
- Consider checking CRP or ESR if there's any clinical suspicion of inflammation 1
- In the presence of inflammation, iron deficiency may exist even with ferritin levels up to 50-100 μg/L 1
The transferrin saturation of 15% is the definitive finding that confirms functional iron deficiency regardless of the ferritin level 3, 4
Expected Response to Treatment
With appropriate oral iron supplementation:
- TSAT should normalize (>20%) within 2-3 months 1
- Ferritin should increase to >50 μg/L, ideally >100 μg/L 1
- Symptoms (if present) should improve within weeks 1
If no response occurs after 3 months of adequate oral iron, consider: 2
- Non-compliance or inadequate dosing
- Malabsorption (celiac disease screening with tissue transglutaminase antibodies)
- Ongoing blood loss exceeding replacement
- Need for GI evaluation at that point