Evaluation of the CEDIA digoxin assay on Boehringer Mannheim/Hitachi 717 analyzer.

Some aspects of a new homogeneous enzyme immunoassay for the determination of digoxin have been evaluated, as part of a multicenter project. The CEDIA Digoxin assay is based on the use of two beta-galactosidase fragments (EC 3.2.1.23) produced by recombinant DNA techniques, one of them linked to digoxin. These two fragments couple to form the complete active enzyme, if not hindered by anti-digoxin antibodies. Digoxin in serum competes for antibody binding. The procedure can easily be automated and does not require special equipment. The imprecision of the method was studied at three different concentration levels (0.56, 1.29 and 2.77 ng/mL of digoxin). Within-run coefficients of variation were 8.01%, 5.57% and 3.30%, respectively, the corresponding between-day CVs being 17.4%, 8.41% and 4.89%. The procedure was found to be linear up to 4.4 ng/mL. Reagents were stable for at least four weeks. Results obtained by the CEDIA Digoxin assay compared well with those obtained by fluorescence polarization immunoassay.

Results of the multicenter evaluation of a novel homogeneous immunoassay for digoxin based on the cloned enzyme donor immunoassay technology.

A new CEDIA assay for the measurement of digoxin in serum on random access analyzers was evaluated by twelve laboratories in Europe and the United States. Studies on the analytical range, reproducibility, calibration stability, recovery in controls, interlaboratory comparability, comparability with routine methods, and the effect of various interfering factors have been performed and the results are presented in this paper. The analytical performance was comparable to that of routine methods provided the manual pipetting step for pre-incubation was performed with accurate pipettes. A major advantage of the CEDIA Digoxin assay in terms of convenience is the simple two-point calibration procedure. Moreover, digoxin can be determined within 15 minutes after receiving the samples on random access analyzers like Boehringer Mannheim/Hitachi analysis systems. Thus, the CEDIA Digoxin assay represents an attractive alternative to the measurement of digoxin on dedicated immunochemical assay systems.

Urinary enzyme activities in patients treated with gold and other antirheumatic drugs.

We have studied 48 rheumatoid arthritis (RA) patients treated with nonsteroidal antiinflammatory drugs (NSAIDs), except salicylates, in 31 of whom parenteral gold was associated as therapeutic agent. In order to assess initial tubular involvement, the activities of some urinary enzymes were measured: N-acetylglucosaminidase (NAG, EC 3.2.1.30), microsomal amino-peptidase (MAP, EC 3.4.11.2) and gamma-glutamyltransferase (GGT; EC 2.3.2.2). Results were compared with a control group of 51 subjects of similar age, with no rheumatic symptoms and normal renal function. Both groups of patients (31 with gold therapy and 17 without) showed a significantly increased activity of NAG in urine, but the increase was greater in those treated with gold. MAP and GGT were not elevated significantly in either group. There was no correlation, however, between the increase of NAG and the cumulative dose of gold. NAG, MAP and GGT activities in serum yielded no relevant information. All the usual tests of renal function were also normal. Determination of NAG in urine may be regarded as a sensitive test, capable of detecting selective involvement of renal tubular cells, whose final diagnostic and prognostic significance merits further evaluation.

Mathematical treatment of data for calculating activities of alpha-amylase isoenzymes.

Methods for determining alpha-amylase isoenzymes by selective inhibition with a wheat-germ protein are practical and easy, and give accurate, precise results. The incomplete specificity of the inhibitory action is not a major drawback but does necessitate mathematical treatment of the data (i.e., enzymic activities measured before and after preincubation with the inhibitor) to ascertain the amount of the different isoamylases. Such an algorithm is quite simple and straightforward, because the isoenzymes can be calculated either arithmetically or geometrically, by using a linear standard curve, empirically obtained, that relates the fraction of activity remaining after inhibition (R/T) to the pancreatic isoenzyme fraction or to the percentage of total alpha-amylase (P/T or 100 X P/T). An alternative method, plotting R/T against the ratio of pancreatic to salivary isoenzyme (P/S), is inconvenient, necessarily yields a nonlinear curve, needlessly complicates the calculations, and has been a persistent source of confusion in many articles dealing with the differentiation of isoamylases.