Breath ammonia test for chronic kidney disease screening: impact of fasting on diagnostic accuracy

Chronic kidney disease (CKD) is a global health concern and early detection is crucial for preventing progression. Current screening methods are inconvenient and resource intensive. Breath ammonia has been proposed as a non-invasive biomarker for renal dysfunction but its diagnostic accuracy and the impact of fasting remain unclear. This study aimed to validate the breath ammonia test for CKD screening and assess the effect of fasting on its diagnostic performance.

This prospective study included 244 participants: a derivation cohort (n = 121) and a validation cohort (n = 123). Breath ammonia was measured using a vertical-channel organic semiconductor sensor. Estimated glomerular filtration rate (eGFR) was calculated using the Modification of Diet in Renal Disease equation. Receiver operating characteristics (ROC) curve analysis was used to evaluate diagnostic performance, and fasting was defined as ≥4 hours without intake.

The average age of the participants was 60.7 years, with males comprising 51% of the cohort. Breath ammonia levels significantly correlated with serum creatinine (r = 0.695, P < .001), eGFR (r = -0.533, P < .001) and blood urea nitrogen (r = 0.765, P < .001). Using a cut-off of 886 ppb, breath ammonia predicted eGFR <60 ml/min/1.73 m² with a sensitivity of 78.5% and a specificity of 81.6% (area under the ROC = 0.842). Fasting enhanced diagnostic accuracy, improving sensitivity and specificity to 87.9% and 91.5%, respectively (area under the ROC = 0.939). Conversely, non-fasting patients demonstrated lower sensitivity and specificity at 74.5% and 74.6%, respectively.

The breath ammonia test is a promising non-invasive CKD screening tool. Standardizing pretest fasting may further improve its diagnostic accuracy.