A comparative study of blood lactate analytic methods.

Three different blood lactate analytic methods were tested for precision, accuracy, linearity, and intermethod comparison: a photoenzymatic assay (PHE), and three electroenzymatic (EE) semiautomatic assays (EE1, EE2, EE3). Reference standards and duplicate capillary blood samples from the earlobe were used. Precision and accuracy of the three techniques, when measuring L-lactate standards, were good in the whole range of measurement (mean variation coefficient, VC = 1.78-3.38%; mean difference = 1.81-3.38%). Correlation between the three methods was high (r = 0.913-0.946), but all three electroenzymatic techniques systematically measured lower values as compared to the PHE tests. The differences ranged from 0.1-1.2 (5 mmol.l-1 PHE level), to 3.4-5.7 (20 mmol.l-1 PHE level). These differences were drastically reduced when a hemolyser and a glycolytic inhibitor were added to the sample prior to the assay. The measurements obtained in capillary blood by the three techniques are not equivalent. The differences are partially attributed to the fact that the PHE technique measures total blood lactate, while the EE methods only measure plasmatic-extraerythrocytic lactate. Some regression equations are presented that may be used to convert values measured by the PHE technique, to EE values and vice versa.