Photoacoustic detection of ammonia exhaled by individuals with chronic kidney disease.

Ammonia (NH3) has been reported as a breath biomarker for chronic kidney disease (CKD) usually detected at concentrations greater than 0.25 parts per million by volume (ppmV). NH3 was detected in breath of individuals with CKD through gaseous photoacoustic spectroscopy (PAS). The efficiency of hemodialysis (HD) was demonstrated. Eight volunteers aged between 20 and 60 years and without previous respiratory disease were eligible, among which six were control volunteers (CV) and two volunteers with advanced CKD, named CKDV1 and CKDV2. The presence of CKD was confirmed by the calculation of creatinine clearance (CC) according to the Cockcroft-Gault equation. Before HD, the mean NH3 concentration exhaled by CKDV1 was 0.9 ± 0.1 ppmV and after HD was 0.20 ± 0.03 ppmV, which demonstrated an efficiency of 76% NH3 reduction in breath. The CKDV2 exhaled 1.27 ± 0.03 ppmV of NH3 pre-HD and 0.42 ± 0.08 ppmV post-HD, which resulted in efficiency of about 67%. It was not possible to quantify NH3 from CV, what led us to infer that all of them exhaled amounts below the detection limit, i.e., 0.20 ppmV. This assumption is underpinned by CC, whose values hovered at 90 ≤ CC ≤ 120 mL/ min, confirming normal renal function.