Setting reference values in trichology

Background: In clinical trichology, reference values are often arbitrary. The difficulty in setting them up depends mostly on the presence of the androgenetic alopecia (AGA) genotype in subjects with clinically unapparent forms. Prepubertal children, who lack 5α-reductase (a real indicator of the AGA phenotype), might provide reference values independent from AGA. We verified whether the vertex/occiput ratios (V/O) of hair density and the V/O of hair diameter are suitable parameters. Methods: In sixty 4-10-year-old Caucasian children, we measured the ratio between the hair density at the vertex and the occiput. The same was done for the diameter. Results: The V/O of density averaged 1.07 ± 0.17 and the V/O of diameter 1.02 ± 0.11. Conclusions: Taking the mean ± 2SD as normal values, our "normal" V/O of density ranged between 0.73 and 1.41 and our "normal" V/0 of diameter between 0.8 and 1.24. People with lower ratios would have, therefore, AGA with 95% of probability. Moreover, we found that hair shedding using the hair pull test and the modified wash test come to 1-2 hairs/day.