What bloodwork is needed to determine if low ferritin is causing my hair loss, and how can I differentiate it from the effects of switching to Mirena and starting Levothyroxine?

Bloodwork for Ferritin-Related Hair Loss and Differentiating from Medication Changes

Order a complete blood count (CBC), serum ferritin, thyroid-stimulating hormone (TSH), and consider adding transferrin saturation to evaluate your hair loss, with ferritin being the single most important test to assess iron stores. 1, 2

Essential Laboratory Tests

Core Iron Studies

• Serum ferritin is the most specific indicator of depleted iron stores and should be checked in all patients with chronic hair loss 1, 2
• A ferritin level ≤15 μg/L confirms iron deficiency in women of childbearing age with 98% specificity 1
• However, for hair loss specifically, recent evidence suggests ferritin <60 ng/mL may be inadequate for optimal hair growth, even though this is above the traditional cutoff for iron deficiency 3
• Complete blood count (CBC) to assess hemoglobin, mean corpuscular volume (MCV), and red blood cell indices 4, 5

Additional Iron Parameters

• Transferrin saturation (calculated from serum iron and total iron-binding capacity) is less affected by inflammation than ferritin and may be more reliable in some cases 4
• Consider serum iron and total iron-binding capacity if ferritin appears "normal" but iron deficiency is still suspected 2

Thyroid Function

• TSH level is essential since you recently started levothyroxine - inadequate thyroid replacement or overtreatment can both cause hair loss 6
• This helps differentiate whether hair loss is from thyroid dysfunction versus iron deficiency 6

Supplementary Tests

• Vitamin D (25-hydroxyvitamin D) levels, as deficiency is commonly associated with diffuse hair loss 6
• Vitamin B12 and folate if dietary deficiency is suspected, though these are less commonly causative 6

Critical Interpretation Pitfalls

Ferritin as an Acute-Phase Reactant

• Ferritin can be falsely elevated during infection, inflammation, or chronic disease, potentially masking true iron deficiency 1, 2
• If ferritin is "normal" (15-60 ng/mL range) but you have microcytic anemia or low MCV, iron deficiency may still be present 2
• In this situation, check transferrin saturation and serum iron/TIBC to confirm iron status 4, 2

Optimal Ferritin Thresholds for Hair

• Traditional cutoffs for iron deficiency (≤15 μg/L) may be too low for hair health 3
• Recent research suggests ferritin ≥60 ng/mL (corresponding to hemoglobin ≥13.0 g/dL) may be necessary for adequate hair growth 3
• This means you could have "normal" ferritin by standard definitions but still have iron-insufficient hair loss 3

Differentiating Causes of Your Hair Loss

Timeline Analysis

• Iron deficiency hair loss typically manifests as chronic diffuse telogen effluvium and develops gradually over months 7, 3
• Medication-related hair loss (from Ryeqo to Mirena switch or levothyroxine initiation) usually appears 2-4 months after the medication change as telogen effluvium 3
• Document when each medication change occurred relative to when hair loss began

Hormonal Considerations

• Mirena (levonorgestrel IUD) can cause hair loss through androgenic effects, though this is less common than with systemic hormonal contraceptives
• Levothyroxine - both hypothyroidism and hyperthyroidism cause hair loss, so inadequate or excessive replacement can be culprit
• The Ryeqo to Mirena switch represents a change from systemic to local hormonal exposure, which could trigger telogen effluvium

Response to Iron Supplementation

• If ferritin is low (<60 ng/mL) and you supplement iron, improvement within 3-6 months strongly suggests iron-deficiency as the cause 3
• Starting iron supplementation within 6 months of hair loss onset results in better prognosis 3
• Lack of response to iron supplementation (when ferritin normalizes) suggests medication or other causes 8

Practical Testing Algorithm

1. Obtain baseline labs now: CBC, ferritin, TSH, transferrin saturation, vitamin D 1, 4, 2, 6

2. Interpret ferritin in context:

   • If <15 μg/L: definite iron deficiency 1
   • If 15-60 ng/mL: possible iron-insufficient for hair growth 3
   • If >60 ng/mL with normal CBC: iron deficiency unlikely as primary cause 3

3. Check TSH adequacy: Ensure levothyroxine dose is appropriate and you're not over- or under-replaced 6

4. Consider trial of iron supplementation if ferritin <60 ng/mL, even if technically "normal" 3

5. Recheck ferritin and hemoglobin every 3 months during supplementation to monitor response 3

Key Clinical Points

• Multiple causes can coexist - you may have both iron deficiency AND medication-related hair loss 3, 6
• The duration of hair loss before treatment is an important prognostic factor - earlier intervention yields better outcomes 3
• If ferritin is low, treat it regardless of whether medications are also contributing, as correction improves prognosis 3
• Consider checking tissue transglutaminase (TTG) antibodies if unexplained iron deficiency is found, to rule out celiac disease 2