The reliability and smallest detectable difference of the Severity of Alopecia Tool score in alopecia areata

The Severity of Alopecia Tool (SALT) score is widely used. However, its inter- and intrarater reliability and smallest detectable difference (SDD) have not been rigorously evaluated.

To determine the interrater and intrarater reliability of the SALT score and to quantify its SDD across different levels of disease severity. We assessed the diagnostic accuracy of the SALT score for identifying key clinical thresholds [for example, SALT score of ≥ 50% (SALT 50)].

Ten patients were scored live by 3 experienced raters, and 53 patients were scored by 11 raters based on photographic records. After a 2-week interval, nine raters performed test-retest scoring.

Interrater and intrarater reliability were excellent, with intraclass correlation coefficients (ICCs) of 0.949 (11 raters, photo-based) and 0.966 (9 raters, photo-based), respectively. SDD was lowest in minimal disease (2.53%) and highest in extensive disease (up to 27.84%). SALT 50 was identified with 97.08% accuracy, although accuracy dropped to 72.73% when only patients between SALT 40 and SALT 60 were considered. Intrarater reliability was consistently higher than interrater reliability, particularly in patients with a high disease burden.

The SALT score demonstrates high inter- and intrarater reliability, particularly at the extremes of disease severity. However, moderate variability in midrange scores affects classification near clinical trial thresholds. Rater training and integration of standardized scoring aids may improve its performance.