Are blood ketones a better predictor than urine ketones of acid base balance in diabetic ketoacidosis

Detection of ketonaemia is a key factor in diagnosing diabetic ketoacidosis (DKA). Measurement of urinary ketones via the nitroprusside reaction is the most commonly employed diagnostic test; however, near patient testing of blood ketones is now widely available. In the clinical setting we wished to compare the utility of urine and blood ketone measurements to predict acid base balance and need for admission in patients with type 1 diabetes. A retrospective study was performed on 52 patients referred to the metabolic or acute receiving units of a teaching hospital. Urine and capillary ketone measurements, blood gas analysis and/or venous bicarbonate measurement were analysed together with the clinical outcome of either admission or discharge of the patient. Capillary β-hydroxybutyrate measurement gave a strong negative correlation (r -0.771; p<0.001) with serum bicarbonate concentration. Urine ketone measurement showed a weaker negative correlation (r -0.493; p<0.001) with bicarbonate levels. There was no difference in the ability to predict hospital admission between blood ketone measurement and urine ketone measurement )positive predictive value 84.6% [95% confidence interval 73.2–95.9%] vs positive predictive value 75.0% [95% confidence interval 62.2–87.8%], respectively). The findings of this study suggest that blood ketone measurement is a better predictor of acid base status than urine ketone measurement. Copyright © 2010 John Wiley & Sons.