A critical review of melatonin assays: Past and present

Abstract

There has been increased interest in the measurement of melatonin in plasma and saliva recently either as a marker of circadian phase or to understand the physiological role of melatonin. For both situations, there is a need for a specific assay for melatonin that is sensitive enough to detect low concentrations (<2 pg/mL). Since the mid‐1970s, there have been many assays developed to measure melatonin in blood and saliva. Radioimmunoassays and ELISA have predominated because of their relative simplicity and high throughput. In this review, I show that the early radioimmunoassays while providing valuable information about nocturnal melatonin levels in humans, generally produced inaccurate basal (daytime) levels. Mass spectrometry assays, however, have provided us with the target values that immunoassays need to achieve, that is, daytime plasma melatonin levels <1 pg/mL. There are now many contemporary commercial assays available utilising both RIA and ELISA technologies, but not all achieve the standards set by the mass spectrometry assays. The performance of these assays is reviewed. I conclude with recommendations on issues researchers need to consider when conducting melatonin studies, including the importance of time of day of collection, validation of assays, the potential causes of poor assay specificity at low levels, the advantages/disadvantages of using saliva vs plasma and extraction assays vs direct assays, kit manufacturers responsibilities and the reporting requirements when publishing melatonin studies.

Melatonin Content of Human Milk: The Effect of Mode of Delivery

“…We collected samples in dim light of less than 30 lux and carefully protected the samples from light by covering the collection containers with opaque paper; this methodology could have influenced the results because if samples were collected under natural lighting, the observed values can decrease. 18,19 We found a melatonin circadian rhythm in breast milk irrespective of the mode of delivery (vaginal or elective cesarean section). Only mothers with normal gestation were recruited.…”

Circulating neurohormone imbalances in canine sudden acquired retinal degeneration syndrome and canine pituitary‐dependent hypercortisolism

“…Although these kits were not previously validated for use with canine serum or plasma, human and canine melatonin are predicted to be identical, and it was anticipated that assays developed for human samples would also be suitable for canine samples, as previously described for a melatonin radioimmunoassay . In accordance with recent recommendations for reporting of neurohormone assays in publications, we calculated inter and intra‐assay coefficients of variation for canine samples, and present these data in comparison with manufacturer's published data in Table . In addition, any values obtained that were less than the lowest standard were reported as that value and used in statistical analysis.…”

Microbial production of beneficial indoleamines (serotonin and melatonin) with potential application to biotechnological products for human health

“…Some of the first techniques described for indoleamine detection, especially for melatonin, are thin layer chromatography (Costantini and Paoli 1998), gas chromatography and mass spectroscopy (Best et al 1993), radioimmunoassay (Van Tassel et al 2001) and enzyme-linked immunosorbent assay (Maldonado et al 2009) (Table 2). Although enzyme-linked immunosorbent assays are simple, rapid, and low cost, they have the disadvantage of the cross-reactivity between other compounds with a similar structure, which traduces in low specificity (Kennaway 2019). In the last decade, different cutting-edge methods of analytical chemistry were developed.…”