Background: Indoxyl sulfate (IS) is a protein-bound solute, which is progressively retained in blood according to the decline of renal function. However, clinical relevance of excess IS in hemodialysis (HD) patients remains unknown.
Patients and methods: We measured serum IS and clinical parameters including pentosidine, carboxymethyllysine (CML) and homocysteine levels in 55 HD patients (age: 67 +/- 2 years, time on HD: 67 +/- 11 months, male/female = 30/25), and examined the relationship between IS and these data.
Results: Serum IS was markedly increased in HD patients (80.49 +/- 6.17 microg/ml) compared to normal range (< 1.9 microg/ml). IS was significantly and positively correlated with time on HD (p < 0.01), blood urea nitrogen (p < 0.01), beta2-microglobulin (p < 0.03), and protein catabolic rate (PCR) (p < 0.01). The patients with increased IS needed a higher erythropoietin dosage. Blood IS was positively correlated with pentosidine (r = 0.505, p < 0.01) and CML (r = 0.275, p < 0.05). In contrast, blood IS was not associated with nutritional and inflammatory parameters. A stepwise multiple regression analysis revealed that time on HD, PCR and pentosidine were significant determinants of IS.
Conclusions: Serum IS was related to time on HD and dietary protein intake. Accumulated IS may be associated with enhanced carbonyl stress in chronic HD patients.