A simple immunoradiometric assay for measuring the entire molecules of adrenomedullin in human plasma

We developed a one-step two-site immunoradiometric assay (IRMA) using two k inds of monoclonal antibodies, which enables us to directly measure the ent ire molecules of adreno-medullin (AM) (the sum of mature-type AM (abbreviat ed, m-AM) amidated at the C-terminus and Gly-extended non-amidated AM) in h uman plasma using a small amount of sample (100 mu l) without prior extract ion. The detection limit of this assay was 0.5 pmol/l for a 100-mu l sample . Intra- and inter-assay precisions were 3.4-7.3% and 5.8-7.6%, respectivel y. The dilution curves of plasma samples showed good linearity and analytic al recovery was 89-118%. The mean total AM in plasma of healthy subjects wa s 9.00+/-2.13 pmol/l, whereas m-AM was 1.05+/-0.24 pmol/l. This method, tog ether with our previously reported simplified method to specifically measur e m-AM (Ohta et al., Clin Chem 1999;45.244-251), allows facile estimation o f the plasma concentration of AM-Gly by subtracting m-AM from the total AM measured by the procedure described in this paper. We were able to show tha t the concentration of total AM in patients with sepsis was markedly higher than that in the healthy controls and that the ratios of m-AM/total AM wer e significantly different between the controls and patients. (C) 1999 Elsev ier Science B.V. All rights reserved.