Hippuric acid and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid in serum and urine. Analytical approaches and clinical relevance in kidney diseases.

Hippuric acid (HA) and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (FA) were determined in serum, plasma, ultrafiltrate and urine by gas chromatography (GC), high-performance liquid chromatography and GC with mass-selective detection, and the methods were compared. As determined by affinity chromatography and analysis of serum and ultrafiltrate, 0.5% of FA in serum occurs free and 99.5% is bound to albumin. In haemodialysed patients with chronic renal failure, the plasma levels of HA and FA are elevated in comparison with normal controls and hospital patients without kidney diseases: HA, 11.1 +/- 5.7 mg/dl (n = 86); FA, 1.9 +/- 1.2 mg/dl (n = 86). Gradual increases in HA in serum, depending on the creatinine concentrations, are found in non-dialysed patients with chronic renal failure. By haemodialysis and haemofiltration the HA levels are lowered (53-66 and 30-36%, respectively), whereas FA is not dialysable.