Automated assay for plasma D-lactate by enzymatic spectrophotometric analysis with sample blank correction

Abstract

D-lactate is essentially a product of bacterial metabolism, and its assessment in plasma has been mainly used to diagnose D-lactic acidosis in patients with short bowel syndrome. In the last few years, there has been growing interest in the use of subclinical elevations of D-lactate concentrations as a diagnostic tool in a variety of clinical conditions such as ischaemia, trauma or infection. An endpoint enzymatic spectrophotometric assay to measure plasma D-lactate with a sample blank correction was validated on our routine clinical chemistry analyser (Olympus AU640). An ultrafiltration procedure was used in samples with a high L-lactate dehydrogenase (L-LDH) activity in order to avoid underestimation of the D-lactate concentration, when a sample blank was processed. The intra- and inter-assay imprecision were <5.1% and <13.3%, respectively and the mean recovery for the D-lactate assay was 95% (range 88-103%). Samples with L-LDH activity greater than 1500 IU/L required the use of ultrafiltration devices. Plasma D-lactate concentration in our 'non-diseased' paediatric population showed a non-Gaussian distribution--95th percentile equal to 19 micromol/L--and no difference based on gender or age was observed. We have established an accurate, sensitive and precise routine assay for D-lactate measurement in plasma. The assay was used to formulate paediatric reference ranges and will be used to assist clinicians to evaluate 'D-lactate toxicity' in patients with a variety of conditions such as short bowel syndrome, small bowel transplantation and as an early marker of intestinal ischaemia.