Diagnostic Approach to Brittle Nails and Hair Loss

Introduction to Diagnostic Tests

The American Academy of Dermatology recommends determining thyroid function (TSH, free T4), iron stores (ferritin), vitamin D, zinc, and in women, androgen status (free and total testosterone, DHEA-S, androstenedione) in patients with brittle nails and hair loss 1, 2
The European Academy of Dermatology and Venereology suggests that ferritin levels should be evaluated to assess iron stores, as iron deficiency can cause brittle nails 1, 2
The American Academy of Dermatology recommends checking vitamin D levels, as vitamin D deficiency can contribute to nail changes 1, 2
The European Academy of Dermatology and Venereology recommends evaluating zinc levels, as zinc deficiency is associated with brittle nails 1, 2

In women with hair loss and brittle nails, the American College of Obstetricians and Gynecologists recommends evaluating androgen status, including free and total testosterone, DHEA-S, and androstenedione 2
The American Academy of Dermatology suggests that prolactin levels should be checked if menstrual irregularities are present 2

The British Association of Dermatologists recommends performing microscopy with potassium hydroxide preparation to visualize fungal elements, and fungal culture on Sabouraud glucose agar to identify the species 3, 1
The American Academy of Dermatology suggests that bacterial culture should be performed if a bacterial superinfection is suspected, particularly in paronychia 4, 5

The American Academy of Dermatology recommends a step-by-step approach to diagnosis, including taking a medical history, performing a clinical examination, and ordering laboratory tests 1, 2, 6, 7, 8
The European Academy of Dermatology and Venereology suggests that the medical history should include questions about medication use, such as taxanes, EGFR inhibitors, and retinoids, which can cause dose-dependent nail brittleness and hair changes 6, 7, 8
The American Academy of Dermatology recommends performing a clinical examination to evaluate nail texture and appearance, and to check for signs of paronychia or other nail infections 1, 3

The American Academy of Dermatology warns against assuming a fungal infection without laboratory confirmation, as nail texture in non-infectious conditions is typically not soft and brittle-crumbly like in fungal infections 1
The British Association of Dermatologists notes that iron deficiency screening is not routinely indicated in patients with alopecia areata, as studies have not consistently shown a link between iron deficiency and alopecia areata 9
The American Academy of Dermatology recommends considering biotin supplementation only in patients with confirmed brittle nails, as 2.5 mg daily has shown 63% clinical improvement in brittle nails, but not in well-nourished patients without nail problems 1