We aimed to compare the recent practical method of capillary beta-hydroxy butyrate (betaOHB) measurement with the widely used urinary ketone measurement in monitoring metabolic status of the patient during treatment of diabetic ketoacidosis (DKA) and diabetic ketosis (DK). Patients with DKA and DK admitted to the hospital were followed with simultaneous measurements of capillary betaOHB by electrochemical method (Medisense Optium, Abbott), and urinary ketone by semi-quantitative method. Blood gases were measured in 2-4 h intervals. Fourteen patients with DKA/DK (7 males and 7 females, age: 9.2 +/- 4.2 years) were included with 50 simultaneous measurements of capillary and urinary ketone. No correlation was detected between urinary ketone and blood pH (P = 0.06) and HCO3 (P = 0.79), whereas a significant negative correlation was found between capillary betaOHB and blood pH (r = -0.41, P < 0.05) and HCO3 (r = -0.35, P < 0.05). Capillary betaOHB and urinary ketone levels did not correlate at the beginning and 3.3 +/- 1.4 h after treatment, but did correlate in the third samples taken 7.8 +/- 2.0 h after treatment (r = 0.8, P < 0.05). Capillary betaOHB levels show good correlation with the degree of acidosis (pH and HCO3). Capillary betaOHB measurement is more sensitive than urinary ketone measurement in reflecting the patient's metabolic status and improvement during treatment.