Whole blood lactate

M. Kyrolainen, H. Hakanson, B. Mattiasson and P. Vadgama, Minimal fouling enzyme electrode for continuous flow measurement of whole blood lactate, Biosens. Bioelectron., 11 (1997) 1073-1081. 

A different lactate biosensor was proposed by Pfeiffer et al. [152], who used an enzyme sandwich membrane that was commercially available for whole blood lactate analysers. The membrane was inserted into a flow cell connected to a microdialysis probe. This membrane showed a significant day-to-day variation in sensitivity ( 50%), but no trend in sensitivity decrease. The problem of rejecting interference has not been completely solved by this system. However, the continuous monitoring of subcutaneous lactate was feasible at least in small rodents, and results were consistent with liquid chromatographic measurements performed on dialysate samples collected during the in vivo experiment. 

Polyurethane-immobilized LOD is being used for whole blood lactate determination in the Glukometer as well as in the ECA 20 (ESAT 6660). Dilution of the samples with the buffer described in Section 5.2.3.1 provides both complete inhibition of glycolysis and immediate hemolysis. As is shown by the correlation equations the method is quite reliable ... 

Initial fluid resuscitation consists of isotonic crystalloid (0.9% sodium chloride or lactated Ringer s solution), colloid (5% Plasmanate or albumin, 6% hetastarch), or whole blood. Choice of solution is based on 02-carrying capacity (e.g., hemoglobin, hematocrit), cause of hypovolemic shock, accompanying disease states, degree of fluid loss, and required speed of fluid dehvery. 

Kost GJ, Nguyen TH, Tang Z. Whole blood glucose and lactate trilayer biosensors, drug interference, metabolism and practice guidelines. Arch Pathol Lab Med 2000 124 1128-34. 

Livesley B, Atkinson L. Letter Accurate quantitative estimation of lactate in whole blood. Clin Chem 1974 20 1478. 

The results indicate that the linear ranges of glucose and lactate (oxidase reactions) in whole blood correspond well with those of the same metabolites in buffers. The sensor methods and the reference methods were in good correlation for all analytes. The precision for the standards in buffers was always better (about 2-3%) than that of the blood samples. This was ascribed in part to the instability of the metabolite concentrations in blood, particularly that of lactate. In addition, the blood viscosity and the nonspecific heat in the reaction can also affect the final results. 

Application of the miniaturized biosensors for metabolite estimation in whole blood is another important concept for future development. The improvement in sensitivity, linear range and response time was achieved by miniaturization of the sensors and has been proven in the case of whole-blood glucose, urea and lactate. A useful feature of miniaturization is that the smaller the flow channel, the smaller are the dispersion and dilution effects, favouring whole blood measurement with minimum error. In the case of clinical estimations, the results of the measurement on miniaturized thermal biosensor are more reliable. 

Other lactate analyzers use lactate oxidase (LOD). Clark et al. (1984b) use the enzyme in the YSI23L instrument (USA) as immobilized between a cellulose acetate membrane and a polycarbonate membrane, the latter serving to exclude high-molecular weight interferents. Lactate measurement in whole blood pipetted immediately after withdrawal into the phosphate buffer stream of the analyzer yielded the following correlation with values obtained with deproteinized blood (Weil et al., 1986) ... 

The sensor measures only plasma lactate, whereas the results of the reference method reflect the concentration of lactate in both plasma and erythrocytes. The authors found an average deviation of the sensor values of 5%. This deviation is surprisingly low in view of the high erythrocyte content of blood (hematocrit 10-50%), which should lead to significantly lower lactate values. The authors therefore postulated a uniform distribution of lactate between plasma and blood cells. Given this, however, the deviation of the values measured with the sensor should be even larger, since the real sample volume, i.e., that of plasma, would be much below 25 pi. These contradictory results provoke doubts as to the applicability of the YSI 23L and the recommended procedure to the assay of lactate in whole blood. 

More recently, a polypyrrole-modified s-BLM has been found to be sensitive to hydrogen ions [80]. Concerning pH probes, they could be the basis for monitoring blood gases (oxygen, carbon dioxide) and related variables (pH, Na" ", K" ", Ca " ", Cl ) as well as metabolites (glucose, urea, lactate, creatinine) after suitable modification. It is envisioned that all these could be monitored simultaneously and/or sequentially in a small sample of undiluted whole blood or in plasma [78]. 

Urea and lactate determined in l-/zL whole blood with a miniaturized thermal biosensor Analyst 120 155-60... 

Kost GJ, Nguyen TH, and Tang Z (2000) Whole-blood glucose and lactate - trilayer biosensors, drag interference, metabolism, and practical guidelines. Archives of Pathology and Laboratory Medicine 124 1128-1134. 

The assay principle with lactate oxidase (L-lactate O2 oxidoreduc-tase, E.C.l. 1.3.2) is the same as that described for glucose oxidase (see 3.1, 215-218). The amperometric measurement of the resulting H2O2 is used in a commercial Lactate analyzer, Model 23 L of the Yellow Springs Instruments, Ohio, USA, where the lactate concentration is measured in 25 jxl of whole blood within 45 s. d) assay with decarboxylating lactate oxidase (LO-CO2)... 

Nutritional status assessment for thiamine is generally carried out by assaying the total thiamine in whole blood or erythrocytes, or by measuring the activity of erythrocyte transketolase before and after incubation with exogenous thiamine pyrophosphate. The latter serves as the sensitive index of thiamine nutritional status (Brin 1980). In addition to the enzymatic test, a measure of urinary thiamine in relation to dietary intake has been the basis for balance studies to assess the adequacy of intake. When thiamine excretion is low, a larger portion of the test dose is retained, indicating a tissue s need for thiamine. A high excretion indicates tissue saturation. In the deficient state, excretion drops to zero. Plasma pyruvate and lactate concentrations have also been used to assess thiamine status. 

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