Do different assays for human acylated ghrelin concentrations provide comparable results?

BACKGROUND: Different assays have been used in investigations on human ghrelin blood concentrations. The range of human ghrelin blood concentrations varies markedly between different studies. The variance of reported ghrelin concentrations might be due to patient specific factors, differences in sample processing, different analytical methods and different manufacturers of the assays. It is unknown how well ghrelin concentrations measured by different analytical methods are comparable and few data exist on the validity (for external consistency) of ghrelin assays.

METHODS: We analyzed 256 human plasma samples for acylated ghrelin concentrations with a commercially available enzyme-linked immunoassay (ELISA) and a multiplex analysis kit using Luminex(®) technology.

RESULTS: Both methods yielded ghrelin concentration within the same range. Concentrations measured by ELISA were systematically higher (median 1.4-fold). The measured concentrations of both methods correlated well as shown by a high Pearson's correlation coefficient (0.753, p<0.01). Bland-Altman plotting revealed complementary aspects concerning the agreement of the two tested methods at low and high concentrations.

CONCLUSIONS: We conclude that the two investigated techniques yield results with an acceptable agreement. The agreement of both measurements indicates a good external consistency and reliability of both analytical methods. In the absence of a gold standard for ghrelin measurement, our data are a cross-validation for both methods.