An interlaboratory comparison between similar methods for determination of melatonin, cortisol and testosterone in saliva.

An interlaboratory comparison study for melatonin, cortisol and testosterone in saliva in which five laboratories participated is reported in this study. Each laboratory blindly measured eight samples prepared from natural saliva spiked with melatonin, cortisol and testosterone in the range 0-579 pmol/L for melatonin, 0-90 nmol/L for cortisol, and 0-622 pmol/L for testosterone. The recovery of spiked material for melatonin ranged from 91-110%, from 83-100% for cortisol and from 80-94% for testosterone. The content of natural hormone in saliva was estimated to be between 0.278 and 6.90 pmol/L for melatonin, 0.56 and 6.72 nmol/L for cortisol and 11.9 and 73.8 pmol/L for testosterone. This indicates a large interlaboratory variation. The present study emphasizes the importance of external quality control for the analysis of melatonin, cortisol and testosterone in saliva.