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DEPARTMENT OF CLINICAL CHEMISTRY SHEFFIELD CHILDREN’S NHS FOUNDATION TRUST LACTATE/PYRUVATE RATIO Relevant disorders For the differential diagnosis of elevated lactate only. Related Metabolic Tests Plasma lactate CSF lactate Indication for Test Pyruvate should only be analysed when lactate is elevated to determine the patients redox state. Pyruvate is an end product of glycolysis. It can either be converted to lactate under anaerobic conditions or transported into mitochondria to feed into the Kreb’s cycle under aerobic conditions. Lactate dehydrogenase activity is high in cells and maintains pyruvate and lactate at equilibrium, therefore when pyruvate accumulates so does lactate. The lactate:pyruvate ratio is measured to aid the differential diagnosis of lactic acidaemia. Pyruvate dehydrogenase deficiency leads to the build up of pyruvate and therefore lactate, however the ratio is normal. In mitochondrial disorders, while the lactate is increased, pyruvate is less so and the ratio is abnormally high Methodology LDH PYRUVATE + NADH <-------> LACTATE + NAD Pyruvate in the presence of excess NADH and LDH at pH 7 is converted to lactate and NAD. The fall in concentration of NADH is estimated by measuring its absorbance at 340 nm. Sample requirements Blood or CSF. Samples HAVE to be mixed with Perchloric Acid. Pre weigh a plain tube. Add a known volume of Perchloric acid (PCA) 5.1% v/v – minimum 0.5ml Weigh tube with PCA. Make a note of the weight. DEPARTMENT OF CLINICAL CHEMISTRY SHEFFIELD CHILDREN’S NHS FOUNDATION TRUST Immediately after taking the sample add an equal volume of whole blood or CSF to the tube containing the PCA (collect blood initially into a Lithium heparin tube). Mix well and transport on ice to the lab without delay. Weight the tube again. Note weight of sample added to the tube (this should equal the amount of acid added). Separate and store the clear supernatant at -20 ˚C. Please note the weights on the laboratory request form. Lactate should also be requested on this sample. Transport information/Contact details Transport the sample DEEP FROZEN. Sample MUST arrive at Clinical Chemistry, Sheffield Children’s Hospital frozen. Department of Clinical Chemistry Sheffield Children’s NHS Foundation Trust Western Bank, Sheffield S10 2TH, UK Jennifer Watkinson (BMS 3) 0114 2717445 Turn Around Time 5 – 14 days Reference Ranges Pyruvate analysis may be useful in the differential diagnosis of lactic acidaemia and should only be analysed if the lactate is elevated. The ratio of lactate to pyruvate can be calculated to determine the redox state, upper limit of normal approx 30 but this may be slightly higher in neonates and lower in older children. An elevated redox state may indicate a primary disorder eg. respiratory chain disorder or a secondary disturbance such as hypoxia/ischaemia. In pyruvate dehydrogenase deficiency the ratio will be normal or reduced. References • Olsen C. Clin Chim Acta 33 (1971) 293