FIELD: medicine. SUBSTANCE: 10 mcl plasma or serum blood taken off in patient is placed to the incubation medium of the following composition: pyruvate kinase from Bacillus stearothermophillus (50-10000 U/l), phosphoenolpyruvate as neutral tris-salt (0.3-10 mmole/l), 4,7,13,16,21-pentaoxa-1,10-diazabicyclo-8,8,5-tricosane (up to 30 mmole/l), 50-500 mM buffer, pH 8 (0.10-0.8 mmole/l), manganese or magnesium ions (1-10 mmole/l), lithium chloride (2-100 mmole/l), ADF as free acid (0.5-10 mmole/l), serum lactate dehydrogenase (5000-100000 U/l), glutamic acid dehydrogenase (2500-20000 U/l, determined at 25 C), keto-glutaric acid as free acid (1-10 mmole/l) or glycerol dehydrogenase from Enterobacter aerogenes (50-1000 U/l), glycerol (0.3-3 mmole/l), 4,7,13,16,21-pentaoxa-1,10-diazabicyclo-8,8,5-tricosane (up to 30 mmole/l), NAD (0.1-5.0 mmole/l), buffer, pH 9 (20-500 mmole/l), serum albumin (up to 5 g/l), glutamic acid dehydrogenase (2500-20000 U/l, determined at 25 C), keto-glutaric acid as free acid (1-10 mmole/l), or acetaldehyde dehydrogenase from yeast (50-10000U/l), glycol aldehyde (0.3-30 mmole/l), 4,7,13,16,21-pentaoxa-1,10-diazabicyclo-88,5-tricosane (up to 30 mmole/l). NAD (0.05-2.0 mmole/l), buffer, pH 7-8 (50-500 mmole/l), dithiothreitol (0.1-2 mmole/l), serum albumin (up to 5 g/l), glutamic acid dehydrogenase (2500-20000 U/l, determined at 25 C), keto-glutaric acid as free acid (1-10 mmole/l), or acetaldehyde dehydrogenase (50-10000 U/l), 4-nitrophenyl acetate (0.3-30 mmole/l), 4,7,13,16,21-pentaoxa-1,10-diazabicyclo-8,8,5-tricosane (up to 30 mmole/l), NAD (0.001-0.1 mmole/l), buffer, pH 7-8 (50-500 mmole/l), dithiothreitol (0.1-2 mmole/l), serum albumin (up to 5 g/l), glutamic acid dehydrogenase (2500-20000 U/l, determined at 25 C), keto-glutaric acid as free acid (1-10 mmole/l). Then incubation mixture is incubated at 37 C for 0.1-5 min followed spectrophotometry at 340 nm and potassium ions measurement by calibration curve. EFFECT: improved method of assay. 5 cl
