By which methods can ADMA be measured?

The first methods that were set up to mesure ADMA were based on high-performance liquid chromatography (HPLC). These methods allowed chromatographic separation of the two structurally very similar, but functionally highly different isomers, ADMA and SDMA (Figure 19).
Methods based on chromatographic separation of ADMA and SDMA do have the disadvantage, however, that laborious sample preparation is necessary to detect the minute amounts present in human plasma and serum, which needs large financial and personnel resources.
Therefore, these methods have only been available in few specialized laboratories and they were not useful for clinical routine diagnostic use because these methods only allowed the quantification of a small number of samples per day. The same holds true for more recently developed methods based on mass spectrometry (i.e., LC-MS, LC-MS/MS, or GC-MS).



Figure 19. Separation of a human plasma sample by high performance liquid chromatography (HPLC) for the quantitation of ADMA, SDMA, and L-arginine. L-Homoarginine is added to the sample as a standard. The complete determination of one single sample takes about 50 minutes.


Recently a novel, easy to use enzyme immunoassay has been developed and validated [70]. This assay allows any clinical laboratory in which a standard ELISA plate reader is available to measure ADMA in human plasma and serum. With the help of this assay, the necessary investment in terms of time, cost, and personnnel has been drastically reduced, and large series of samples can now be measured in relatively short periods of time in clinical routine. The ADMA®-ELISA, which is protected by a patent, has been validated by comparing it with state-of-the-art LC-MS and GC-MS techniques. An extraordinarily good correlation of data was found (by comparison with LC-MS/MS, R = 0,984; p < 0.001; N = 29; Figure 20). Cross-reactivities with other L-arginine analogues present in plasma and serum has been found to be negligible (L-NMMA, 1.0%; SDMA, 1.2%; L-arginine <0.02%). The ELISA has a linear range between 0.1 and 3 µmol/l in human serum and plasma and thus covers the whole range of physiological and pathophysiological concentrations. The assay has also been validated for experimental purposes for use in mouse and rat plasma as well as in cell culture supernatants. Presently the ADMA®-ELISA is being used in large patient cohorts from controlled clinicial studies. An updated list of references is available from the editors upon request. More information on ADMA and the ADMA-ELISA can be found on the websites www.germediq.de, and www.dld-diagnostika.de.
 

Abbildung 20. Korrelationsanalyse zwischen den mit dem ADMA®-ELISA bestimmten ADMA-Serumkonzentrationen im Vergleich zur Messung mittels Gaschromatografie-Massenspektrometrie GC-MS. Die gefundene Korrelation zwischen beiden Methoden ist über den gesamten (patho-) physiologisch relevanten Konzentrationsbereich linear und eng und bestätigt die Validität der Messungen mittels des ADMA®-ELISA.