Fingernail and toenail clippings as a non-invasive measure of chronic cortisol levels in adult cancer survivors

Purpose Cancer survivors are at greater risk of comorbidities and functional decline due to physiological and psychological stress which can be measured by salivary cortisol. If saliva is used, multiple samples must be collected to accurately quantify long-term stress; however, fingernail (FN) and toenail (TN) clippings offer an opportunity to measure retrospective cortisol levels in a non-invasive manner. Methods Three sets of FN and TN clippings were collected at 12-month intervals in conjunction with saliva samples from cancer survivors ( n = 109) participating in two clinical trials. FN and TN samples were stored at room temperature (RT); a subset underwent additional processing and freezing before analysis. Cortisol levels were determined via enzyme immunoassay, and correlation coefficients were generated to determine overall correspondence of the individual measures. Results Matched RT and frozen samples were highly correlated for TN ( r = 0.950, p = 5.44 × 10 −37 ) and FN ( r = 0.784, p = 1.05 × 10 −10 ). Correlations between RT FN and TN were statistically significant ( r = 0.621, p = 3.61 × 10 − 17 ), as were frozen FN and TN ( r = 0.310, p = 0.0283). RT, but not frozen TN and FN correlated with salivary cortisol ( r = 0.580, p = 1.65 × 10 − 16 and r = 0.287, p = 0.00042 for TN and FN, respectively). Conclusions FN and TN cortisol levels correlate with salivary cortisol in adult cancer survivors and may offer a less invasive and convenient means for measuring chronic cortisol levels.