Development of an enzymatic assay to measure lactate in perchloric acid-precipitated whole blood.
BACKGROUND
The lactate to pyruvate (L:P) ratio is used to identify the cause of a lactic acidosis. Because tests for whole blood lactate and pyruvate require different sample types, the accuracy of the L:P ratio may be compromised by preanalytical errors. The measurement of lactate in the sample required for pyruvate is desirable.


METHODS
Whole blood was added to 8% perchloric acid to obtain a protein-free supernatant. Lactate was measured by its oxidation to pyruvate and hydrogen peroxide by lactate oxidase. Assay accuracy, imprecision, analytical sensitivity, linearity, analyte stability, and a reference interval were determined.


RESULTS
Deming regression of lactate results from paired plasma and supernatant produced a slope of 0.95 and y-intercept of -0.37 mmol/l (R(2)=0.95). Recovery of lactate added to supernatant ranged from 103.4 to 112.7%. Within-laboratory CVs were 6.1% and 1.1% at 1.58 and 10.89 mmol/l, respectively and between-day CVs were 2.3% and 0.9%, respectively. The limit-of-detection was 0.18 mmol/l and the assay was linear to 13.15 mmol/l. Lactate in the supernatant was stable for a minimum of 8h, 21 days, or 6 months at room temperature, 4-8°C, and -20°C, respectively. The lactate reference interval was 0.31-2.00 mmol/l from 116 healthy adults.


CONCLUSIONS
Lactate can be quantified in the same protein-free supernatant used for the measurement of pyruvate allowing the calculation of the L:P ratio from a single specimen.
ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, UT 84108, USA.
Jun
J
Lu
ARUP Laboratories, Salt Lake City, UT 84108, USA.
Brady S
BS
Pulsipher
ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, UT 84108, USA; Department of Pathology, University of Utah School of Medicine, Salt Lake City, UT 84112, USA. Electronic address: david.grenache@path.utah.edu.
David G
DG
Grenache
D057075:Enzyme Assays; D006801:Humans; D019344:Lactic Acid / Q000097:blood* / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D010472:Perchlorates / Q000737:chemistry*; D019289:Pyruvic Acid / Q000097:blood / Q000378:metabolism
D010472:Perchlorates; D019344:Lactic Acid; D019289:Pyruvic Acid; D006899:Mixed Function Oxygenases; C021497:lactate 2-monooxygenase; C576518:Perchloric Acid
Lactate; Lactate to pyruvate ratio; Lactic acidosis; Perchloric acid; Pyruvate