Eight-month test-retest agreement in morning salivary cortisol, self- and parent-rated anxiety in boys with an Autism Spectrum Disorder

•Cortisol is used in studies of anxiety in children with autistic spectrum disorder.•Some papers have recommended repeated measures of cortisol for reliability.•Cortisol and anxiety samples from 8 months apart were significantly correlated.•Cortisol is influenced by anxiety but may vary in a correlated manner.•Repeated measures of cortisol may not be required for reliability.

The agreement over time in morning salivary cortisol concentrations and also self- and parent-rated anxiety was investigated in a sample of 16 boys with an ASD. Cortisol and anxiety data were collected eight months apart. Results indicated that there were significant correlations between each pair of measures from the two occasions, suggesting that cortisol concentrations and anxiety did not vary much at all over that time, challenging the assumption that cortisol needs to be measured over multiple days to obtain reliable data from children with an ASD. Implications for research into the ways these children respond to chronic stressors are discussed.