Breath acetone is a reliable indicator of ketosis in adults consuming ketogenic meals.

BACKGROUND: Ketogenic diets are used therapeutically to treat intractable seizures. Clinically, it appears that the maintenance of ketosis is crucial to the efficacy of the diet in ameliorating seizures. To understand how ketosis and seizure protection are related, a reliable, noninvasive measure of ketosis that can be performed frequently with minimal discomfort is needed.

OBJECTIVE: The objective was to determine which index, breath acetone or urinary acetoacetate, is more strongly related to the plasma ketones acetoacetate and beta-hydroxybutyrate.

DESIGN: After fasting overnight for 12 h, 12 healthy adults consumed 4 ketogenic meals over 12 h. Blood, breath, and urine samples were collected hourly. Blood was analyzed for plasma acetoacetate and beta-hydroxybutyrate, breath for acetone, and urine for acetoacetate.

RESULTS: By the end of the 12-h dietary treatment, plasma acetoacetate, plasma beta-hydroxybutyrate, and breath acetone had increased 3.5-fold, whereas urinary acetoacetate increased 13-fold when measured enzymatically and 25-fold when measured with urinary ketone dipsticks. Plasma acetoacetate was best predicted by breath acetone (R(2) = 0.70, P < 0.0001). Plasma beta-hydroxybutyrate was equally predicted by breath acetone and urinary acetoacetate (R(2) = 0.54, P = 0.0040).

CONCLUSIONS: Breath acetone is as good a predictor of ketosis as is urinary acetoacetate. Breath acetone analysis is noninvasive and can be performed frequently with minimal discomfort to patients. As an indicator of ketosis in epilepsy patients consuming a ketogenic diet, breath acetone may be useful for understanding the mechanism of the diet, elucidating the importance of ketosis in seizure protection, and ultimately, enhancing the efficacy of the diet by improving patient monitoring.