Plasma Kynurenic Acid/Tryptophan Ratio: A Sensitive and Reliable Biomarker for the Assessment of Renal Function

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.