BACKGROUND: Decreased tryptophan (TRP) and increased kynurenine (KYN) and 
kynurenic acid (KYNA) in blood have been reported in patients and experimental 
animals with renal diseases. We investigated if these compounds could be used as 
new biomarkers for the assessment of renal function.
METHODS: Eighty hospitalized hypertensive patients (20 with chronic kidney 
disease (CKD), and other 60 were considered as control) were enrolled for the 
investigation. Plasma TRP, KYN, and KYNA were determined by high-performance 
liquid chromatography. Change rate (CR) was employed to evaluate the sensitivity 
of the parameters of renal function.
RESULTS: CR of plasma KYNA/TRP ratio (+103%) was much higher than the CRs of 
blood urea nitrogen (+44%), serum creatinine (+56%) and estimated glomerular 
filtration rate (-35%). Plasma KYNA/TRP ratio was in close relationship with 
blood urea nitrogen (r = 0.622), serum creatinine (r = 0.797), urine 
micro-albumin/24-h (r = 0.518) and estimated glomerular filtration rate (r = 
-0.662), respectively, with all p-values <0.001.
CONCLUSIONS: Plasma KYNA/TRP ratio was sensitive and reliable to indicate renal 
function and could be used as a new biomarker to assess the risk or presence of 
kidney disease.