Urinary L-lactate excretion is increased in renal Fanconi syndrome

Background. Measurement Of L-lactate in body fluids is an established clinical tool to identify disorders of cellular respiration. However, there is very little known about the clinical value of urinary lactate measurements. We investigated urinary lactate excretion in children with renal Fanconi syndrome. Methods. Freshly voided urine samples were obtained from children with Fanconi syndrome and controls both with and without renal disease. Urine lactate was estimated by conversion to pyruvate in the presence of lactate dehydrogenase and NAD. The NADH produced was measured photometrically. Urine lactate was factored for urine creatinine. Results. Children with Fanconi syndrome had a significantly higher urine lactate/creatinine ratio [mean: 84 x 10(-2) mmol/mmol; 95% confidence interval (CI): 40.8-127.1 x 10(-2) mmol/mmol] than healthy controls (mean: 1.3 x 10(-2) mmol/mmol; CI: 1.1- 1.5 x 10(-2) mmol/mmol) and those with a variety of renal diseases (mean: 3.1 x 10(-2) mmol/mmol; CI: 1.8-4.5 x 10(-2) mmol/mmol). Conclusions. Urinary lactate is increased in Fanconi syndrome. The increase is likely to be due to reduced lactate co-transport in the proximal tubule. Urinary lactate/creatinine has clinical utility as a sensitive test of disordered proximal renal tubular function.