What is the difference between iron and ferritin labs in a female patient with hair loss potentially related to iron deficiency?

Understanding Iron vs. Ferritin Labs in Female Hair Loss

Serum iron (measured as transferrin saturation or TSAT) reflects iron immediately available for red blood cell production, while serum ferritin reflects total body iron stores—ferritin is the single most important test for assessing iron deficiency in women with hair loss. 1, 2

Key Physiological Differences

Serum Iron/Transferrin Saturation (TSAT):

• Measures iron currently circulating in blood, bound to transferrin protein and ready for immediate use in erythropoiesis 3
• Calculated as: (serum iron × 100) ÷ total iron binding capacity (TIBC) 3
• Shows significant diurnal variation throughout the day, making it less reliable as a standalone marker 3
• TSAT <16% defines iron deficiency in healthy individuals 1

Serum Ferritin:

• Reflects iron stored in liver, spleen, and bone marrow reticuloendothelial cells 3
• Serves as the primary indicator of total body iron storage 4
• More stable than serum iron, without significant diurnal fluctuation 5
• Ferritin ≤15 μg/L confirms iron deficiency with 98% specificity in premenopausal women 1

Clinical Application for Hair Loss Evaluation

The American Academy of Dermatology recommends ordering CBC, serum ferritin, TSH, and transferrin saturation as baseline tests for any woman presenting with hair loss. 1 Serum ferritin is prioritized as the single most important test. 1

Diagnostic Thresholds for Hair Loss Context:

• Ferritin ≤15 μg/L: Confirms iron deficiency with high specificity 1
• Ferritin <30 μg/L: Defines iron deficiency without inflammation 1
• Ferritin ≥60 μg/L with Hb ≥13.0 g/dL: Suggested as optimal range for hair growth 1, 6

The corresponding hemoglobin level for adequate hair growth (ferritin 40-60 ng/mL) is 13.1-13.8 g/dL, which is higher than the anemia threshold of 12.0 g/dL. 6 This means women can have "normal" hemoglobin by standard definitions but still have insufficient iron stores for optimal hair follicle function.

Critical Pitfall: Ferritin as an Acute-Phase Reactant

Ferritin can be falsely elevated during infection, inflammation, chronic disease, malignancy, or liver damage, potentially masking true iron deficiency. 1, 2 This is the most important caveat when interpreting ferritin levels.

When Inflammation is Present:

• The lower limit of normal ferritin increases to 100 μg/L 1
• Always assess inflammatory markers (CRP, ESR) alongside ferritin 1
• Transferrin saturation becomes more reliable than ferritin alone, as it is less affected by inflammation 1
• An inflammatory iron block can mimic functional iron deficiency, with TSAT <20% and ferritin 100-700 ng/mL 3

Practical Algorithm for Hair Loss Workup

1. Order both ferritin AND transferrin saturation (with serum iron and TIBC) 1
2. Check inflammatory markers (CRP and/or ESR) simultaneously 1
3. Interpret results based on inflammation status:
   • Without inflammation: Ferritin <30 μg/L or TSAT <16% = iron deficiency 1
   • With inflammation: Ferritin <100 μg/L suggests true deficiency 1
4. Consider celiac screening (tissue transglutaminase antibodies) if unexplained iron deficiency is found 1

Treatment Implications

The American Academy of Dermatology and Cleveland Clinic Foundation support treating iron deficiency without anemia (ferritin ≤15 μg/L, normal hemoglobin) in the context of hair loss. 1, 2 This represents a lower threshold for intervention than traditional hematologic criteria.

Iron supplementation started within 6 months of hair loss onset results in better prognosis. 1, 6 Hair loss from iron deficiency develops gradually over months, not acutely. 1

Monitoring Strategy:

• Recheck ferritin and hemoglobin every 3 months after starting supplementation 1
• Target ferritin ≥60 μg/L with corresponding hemoglobin ≥13.0 g/dL 1
• Patients with subjective hair regrowth show greater increases in ferritin levels after supplementation 6

Evidence Quality Considerations

The relationship between iron deficiency and hair loss varies by hair loss type. Multiple studies found lower ferritin levels in patients with diffuse hair loss, telogen effluvium, and androgenetic alopecia. 1 However, for alopecia areata specifically, evidence is conflicting—only 2 of 8 studies supported an association, with the British Association of Dermatologists stating routine iron testing is not recommended for this condition. 1

One high-quality study found no statistically significant increase in iron deficiency in women with female pattern hair loss or chronic telogen effluvium compared to controls. 7 Despite this, iron deficiency accounted for 70.3% of female alopecia cases in a 2023 study, making it the most common etiology identified. 6