Assay of d-lactate in urine of infants and children with reference values taking into account data below detection limit

Abstract

Accumulation of d-lactic acid produced by intestinal bacteria such as streptococci and lactobacilli has been extensively studied in ruminants [1–4]. In humans an increased production of d-lactate by intestinal bacteria under pathological conditions such as the short bowel syndrome can cause metabolic acidosis [5–8]. Since the lactate assays routinely used only measure l-lactate we developed a sensitive method of d-lactate quantification and established reference values in spot urines of infants and children (0 to 4 years of age). The enzymatic method with fluorimetric quantification of NADH is linear up to 2 mmol/l. It has a detection limit of 3.4 μmol/l. Among structurally related organic acids an interference was found only for l-lactate and dl-2-hydroxybutyrate at concentrations which are way beyond their physiological excretion. One hundred and sixty five spot urines of healthy Swiss (S), Austrian (A), German (G) and Chilean (CHI) infants aged from 0 to 4 years were analyzed. The distribution of the data is close to a lognormal one. Values below the detection limit were simulated and age groups were formed. In all populations d-lactate excretion was found highest during the first year of life; it declines with age during infancy and remains stable from 2.5 to 4 years of age. We show that d-lactate is excreted physiologically by healthy infants and children below 4 years of age and present reference values for d-lactate excretion which show some differences between the populations tested.