Accuracy and reliability of naevus self-counts.

A high number of melanocytic naevi is one of the major risk factors for cutaneous melanoma. Therefore, counting the number of acquired naevi could be a useful strategy to identify individuals at an increased risk for targeted skin cancer screening. The aim of this study was to assess agreement between naevus self-counts and counts of trained examiners as well as to analyse potential determinants of the magnitude of agreement. In a large cross-sectional survey (n=1772), university students counted their naevi on both arms and were additionally examined by specifically trained examiners in a mutually blinded manner. Further data on other melanoma risk factors such as skin phototype, hair colour or freckling were collected by a questionnaire. The relative difference between the two naevus counts and the ratio of the counts were calculated to quantify agreement. Regression modelling was performed to identify independent determinants of agreement. The overall agreement was moderate, with participants counting on average 14% more naevi than the examiners. In terms of the potential determinants associated with agreement, skin type and medical education showed a strong effect. The difference in naevus counts was significantly larger for individuals with lighter skin types compared with those with a dark skin (Fitzpatrick type IV), and medical students yielded a naevus count more similar to the examiner's count than nonmedical students. Naevus self-counts can only provide a rough estimate of the number of naevi, but may not be accurate enough to reliably identify a high-risk group for melanoma screening, especially in individuals with light skin types.