The study subject shall each hour collect his or her urine volume in a specially designated measurement cup. The Urine Volume is noted. 10 ml of the urine are then used to measure the electrolyte concentration. Another 10 ml of urine is saved for further analyses at the Sahlgrenska University central lab. These analyses are routine but samples may be stored for a few days before the measurement takes place. This depends on when the central lab can accept our samples and on their specific working load. Sample storage and handling will be performed according to the central lab recommendations. The samples will at maximum be frozen down once at a temperature of -80°C.