Determination of D-lactate by enzymatic methods in biological fluids: Study of interferences

Abstract

Analysis of nondeproteinized samples with an enzymatic method to determine D-lactate indicated interferences. The presence of L-lactate dehydrogenase (LD) and L-lactate in the sample led to underestimation of D- lactate content when a sample blank was processed and overestimation when it was omitted. We proved that this interference is not due to lack of D-LD stereospecificity. Moreover, assessment of D-LD and L-LD K(M) for NAD+ allowed us to rule out the different affinities for this coenzyme as a cause of the interference. Our results underline the importance of deproteinizing samples for D-lactate analysis when enzymatic methods are used. The ultrafiltration procedure we propose is convenient and shows acceptable mean recovery (108%) and good imprecision (within-run CV = 4.2% and 3,0% for D- lactate at 31 and 107 μmol/L, respectively; between-run CVs were 7.3% at 49 μmol/L D-lactate and 3.1% at 115 μmol/L D-lactate).