Reading a Trichogram: The Pull-Test Ratios a Clinician Interprets

A trichogram generates actual numbers on follicle cycle status — anagen:telogen ratio, dystrophic hairs, vellus proportion. These numbers mean specific things about what is happening at the follicle.

The trichogram is one of the older tools in the clinical hair assessment toolkit, predating dermoscopy and genetic testing by decades. It remains useful precisely because it generates actual proportional data on follicle cycle status — numbers rather than impressions — from a defined scalp area.

The procedure

Trichogram requires hair not to have been washed or styled for 24 hours before testing (to avoid artificially disrupting telogen hairs). A template-guided area (typically 1–2 cm²) is selected, often at the frontal or temporal scalp for AGA assessment or the vertex for crown loss evaluation. Approximately 50–100 hairs are grasped with rubber-tipped forceps and epilated with a rapid traction movement.

The epilated hairs are mounted on a microscope slide and examined under low magnification. Each hair root is classified as anagen (firm, pigmented, enclosed in an inner root sheath), telogen (club-shaped, non-pigmented, no inner root sheath), catagen (intermediate morphology), or dystrophic (broken, malformed — indicating damage rather than normal cycling).

Interpreting the ratios

Anagen >80%: Normal. Expected in healthy scalp.

Telogen >20%: Elevated. Suggests telogen effluvium if acute and diffuse, or advancing AGA if patterned.

High dystrophic anagen: Suggests active destructive process — alopecia areata, chemotherapy, or inflammatory alopecia. The breakage pattern distinguishes this from normal telogen.

Vellus proportion: A significant proportion of miniaturised vellus hairs in a site-specific trichogram is diagnostic for AGA in the appropriate clinical context.

Limitations

Trichogram is semi-invasive (requires epilation), has some variability based on operator technique and patient compliance with the pre-test protocol, and has been largely supplanted by trichoscopy for routine AGA assessment. Its primary current role is in clinical research for objective cycle phase quantification and in evaluating patients where scalp biopsy is not feasible but more data than dermoscopy provides is needed.