Measurement of Hair Cortisol as a Retrospective Stress Marker: Effects of Prewashing, Pulverization, Temperature, and Sonication.

Cortisol deposited in the hair can be used as a tool for the objective assessment of chronic stress. The authors compared the efficiency of cortisol extraction by several methods in different individuals. Hair samples from 20 men were either prewashed or not, and either cut into small pieces with scissors or pulverized using liquid nitrogen. Afterward, temperature (16 hours at 52°C), sonication (2 hours), or both were used to increase the efficiency of methanol extraction. Duplicate samples were analyzed using enzyme-linked immunosorbent assay for cortisol measurement ( n = 480). Cortisol data had a non-normal distribution and are expressed as median. An alpha level less than 0.05 was considered significant. Hair cortisol levels were between 0.3 and 60 pg/mg and differed between the participants ( P < 0.001). No significant difference was noted between prewashing and not prewashing procedures (19.5 vs. 20.6, respectively; P = 0.247). Cutting into small pieces with scissors yielded lower cortisol levels compared with pulverization (17.4 vs. 22.0 pg/mg, P = 0.002); however, no differences were observed when temperature or sonication or both were used (20.2, 19.7, and 19.6 pg/mg, respectively, P = 0.971). Overall, the technique was sensitive to detect varying levels of hair cortisol in each individual. Prewashing, temperature, and sonication were observed to be unnecessary. Although pulverization caused higher hair cortisol extraction (4.6 pg/mg), it was relatively low compared with the large interindividual differences. Thus, any of the methods could be used, especially when the time and cost of analyses are considered.