Abstract
BACKGROUND: The conventional 20% threshold for hair diameter diversity (HDD), widely accepted for diagnosing androgenetic alopecia (AGA) in the vertex area, has not quantitatively analyzed. OBJECTIVE: To validate the HDD 20% threshold for AGA and develop a refined, Korean-specific criterion. METHODS: This study involved 240 male patients with AGA, categorized by the V stages of the basic and specific classification. Phototrichogram images of the vertex region were analyzed using Image J software for hair thickness measurement. RESULTS: Receiver operating characteristic curve analysis determined the 45 μm hair diameter threshold as the most diagnostic for AGA, with an area under the curve value of 0.884 and a Youden index of 0.659. Optimal AGA diagnosis was achieved when over 21% of hair had a diameter of ≤45 μm. LIMITATIONS: Restriction to Korean male limits its applicability to a broader population, and using a specific hair diameter threshold does not account for individual variations in hair characteristics. CONCLUSION: The study validates the conventional HDD 20% threshold and proposes a more appropriate 45 μm threshold for Korean males, beyond the 40 μm. It concludes that while the HDD 20% remains a key method for early detection of vertex AGA, the definition of thin hair should be ethnicity-specific.