Luminometric single step urea assay using ATP-hydrolyzing urease

An automatic enzyme kinetic luminometric method for determination of small quantities of urea in biological fluids and in microdialysates is presented. The method is based on the ATP-hydrolyzing urease reaction [urea amidohydrolase (ATP-hydrolyzing); EC 3.5.1.45], moni-tored by a luciferin-luciferase ATP reaction. The assay range is 100 pmol to 50 nmol with a detection limit of 5 mmol/L in the sample, compared with detection limits of 0.1 mmol/L in earlier spectrophotometric methods. To reduce the non-urea-dependent ATPase activity (vblank) and to increase the urea-dependent activity, 1,2-propanediol was included. Assay conditions were optimized by multi-variate analysis. Recoveries of urea added to blood dialy-sate and plasma were 96–103%. No analytical interference of common metabolites, drugs, or other additives wa