What initial laboratory tests are recommended for a 35-year-old female with hair loss, normal Body Mass Index (BMI), and regular menstrual cycles?

Laboratory Tests for Hair Loss in a 35-Year-Old Female with Normal BMI and Regular Menses

For a 35-year-old female with hair loss, normal BMI, and regular menstrual cycles, the initial laboratory workup should include thyroid function tests (TSH, free T4), complete blood count, ferritin, and androgen panel (total testosterone, free testosterone index, DHEAS).

Initial Laboratory Evaluation

First-Line Tests:

• Thyroid Function Tests

  • TSH (highly sensitive at 98% and specific at 92% for thyroid disorders) 1
  • Free T4 (to differentiate between subclinical and overt thyroid dysfunction)

• Complete Blood Count (CBC)

  • To evaluate for anemia or other hematologic abnormalities

• Iron Studies

  • Ferritin (low levels can cause hair loss even with normal hemoglobin)
  • Serum iron and total iron binding capacity (if ferritin is borderline)

• Androgen Panel

  • Total testosterone (sensitivity 74%, specificity 86%) 2
  • Calculated free testosterone (sensitivity 89%, specificity 83%) 2
  • Free androgen index (sensitivity 78%, specificity 85%) 2
  • DHEAS (dehydroepiandrosterone sulfate) 2

Second-Line Tests (if indicated by history or initial results):

• Nutritional Parameters

  • Vitamin D
  • Zinc
  • Vitamin B12
  • Folate

• Additional Hormonal Tests

  • Prolactin (if galactorrhea or menstrual irregularities develop) 2
  • Androstenedione (sensitivity 75%, specificity 71%) 2
  • LH/FSH ratio (if PCOS is suspected despite regular menses) 2

Clinical Reasoning

The laboratory evaluation is guided by the most common causes of hair loss in women of reproductive age:

1. Androgenetic Alopecia: Most common cause of hair loss in women 3, requiring evaluation of androgen levels even with normal menses.

2. Telogen Effluvium: Often triggered by physiological or emotional stress 3, requiring evaluation of potential metabolic triggers.

3. Thyroid Dysfunction: Both hypo- and hyperthyroidism can cause diffuse hair loss 1.

4. Iron Deficiency: Can cause hair loss even without anemia, making ferritin measurement essential.

Interpretation Guidelines

• Thyroid Function: TSH values below 0.1 mU/L indicate hyperthyroidism, while values above 6.5 mU/L suggest hypothyroidism 1

• Androgen Levels: Calculated free testosterone has the highest sensitivity (89%) for detecting hyperandrogenism 2, making it particularly valuable even in women with regular cycles

• Ferritin: Levels below 30 ng/mL may contribute to hair loss even with normal hemoglobin

Important Considerations

• Regular menses do not rule out hormonal causes of hair loss, as subtle hormonal imbalances can affect hair growth without disrupting menstrual cycles

• Laboratory tests should be interpreted in the context of the pattern of hair loss (diffuse vs. patterned)

• The timing of hormonal tests matters - androgen measurements are most accurate when taken between days 3-6 of the menstrual cycle 2

• High-quality laboratory methods (LC-MS/MS) for androgen measurement provide better specificity (92%) than direct immunoassays (78%) 2

By systematically evaluating these parameters, the underlying cause of hair loss can be identified in most cases, allowing for targeted treatment to improve this condition that significantly affects quality of life.