Intermittent Diffuse Hair Shedding: Vitamin B12 Deficiency is the Primary Culprit
The most likely cause of this woman's two-year intermittent diffuse hair shedding is vitamin B12 deficiency (172 pg/mL), not iron deficiency, as her ferritin of 300 ng/mL is elevated and suggests adequate to excess iron stores. 1, 2
Understanding the Laboratory Values
Ferritin 300 ng/mL - Not Iron Deficient
- Ferritin of 300 ng/mL is well above the threshold for iron deficiency and actually suggests adequate iron stores or possible inflammation 1, 2
- Without inflammation, ferritin <30 μg/L defines iron deficiency; with inflammation present, the lower limit increases to 100 μg/L 2
- For hair loss specifically, ferritin ≤15 μg/L confirms iron deficiency with 98% specificity in premenopausal women 2, 3
- This patient's ferritin is 20-fold higher than the deficiency threshold, making iron deficiency an unlikely cause 4
Critical caveat: Ferritin is an acute-phase reactant and can be falsely elevated during infection, inflammation, chronic disease, malignancy, or liver damage 2. Check CRP and/or ESR to rule out inflammation masking true iron deficiency 2.
Vitamin B12 172 pg/mL - Deficient
- Vitamin B12 deficiency is defined as levels <200 pg/mL 5
- This patient's B12 of 172 pg/mL falls below this threshold and represents true deficiency 5
- Vitamin B12 deficiency that progresses for longer than 3 months may produce permanent degenerative lesions of the spinal cord 6
Recommended Diagnostic Workup
Before initiating treatment, complete the following:
- CBC to assess for anemia (Hb <12 g/dL in women) 3
- TSH to rule out thyroid dysfunction as a contributing factor 3
- Transferrin saturation (from serum iron and total iron-binding capacity) - less affected by inflammation than ferritin 2
- CRP and/or ESR to detect inflammation that could distort ferritin interpretation 2
- Tissue transglutaminase (TTG) antibodies if unexplained deficiency is found, to rule out celiac disease 3
Treatment Approach
Vitamin B12 Replacement - Primary Intervention
Initiate vitamin B12 supplementation immediately given the confirmed deficiency and risk of irreversible neurologic damage 6:
- If pernicious anemia is diagnosed, monthly intramuscular injections of vitamin B12 for life are required 6
- Failure to treat will result in return of anemia and development of incapacitating and irreversible damage to the nerves of the spinal cord 6
- Monitor serum potassium closely during the first 48 hours of treatment and replace if necessary 6
- Obtain hematocrit and reticulocyte counts daily from days 5-7 of therapy, then frequently until hematocrit normalizes 6
Iron Supplementation - Not Indicated
- Do not supplement iron with ferritin of 300 ng/mL unless transferrin saturation is low (<16%) or inflammation is confirmed 2
- If inflammation is present and transferrin saturation is low, consider iron supplementation with a target ferritin ≥60 μg/L 2
Folic Acid Consideration
- Never give folic acid without vitamin B12 in this patient 6
- Doses of folic acid >0.1 mg/day may produce hematologic remission in B12 deficiency but will not prevent neurologic manifestations 6
- Folic acid may mask B12 deficiency while allowing progression of irreversible spinal cord damage 6
- If folate levels are also low, administer folic acid together with vitamin B12 6, 7
Prognosis and Follow-up
- Hair loss due to nutritional deficiency develops gradually over months 3
- Iron supplementation started within 6 months of onset results in better prognosis for iron-related hair loss, but this patient likely has B12-related hair loss 2, 3
- Monitor vitamin B12, folate, iron levels, hematocrit, and reticulocyte counts as outlined above 6
- Re-evaluate if reticulocytes do not increase or if they fail to remain at least twice normal while hematocrit is <35% 6
Common Pitfall to Avoid
The most dangerous error would be treating with folic acid alone or assuming the elevated ferritin indicates iron overload requiring no intervention. Always check inflammatory markers before dismissing iron deficiency based solely on ferritin, and always supplement B12 before or concurrent with folic acid 2, 6.