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Existing handheld glucose meters are glucose oxidase (GO)-based. Oxygen side reactions can introduce oxygen dependency, increase potential error, and limit clinical use. Our primary objectives were to: a) introduce a new glucose dehydrogenase (GD)-based electrochemical biosensor for point-of-care testing; b) determine the oxygen-sensitivity of GO- and GD-based electrochemical biosensor test strips; and c) evaluate the clinical performance of the new GD-based glucose meter system in critical care/hospital/ambulatory patients.Multicenter study sites compared glucose levels determined with GD-based biosensors to glucose levels determined in whole blood with a perchloric acid deproteinization hexokinase reference method. One site also studied GO-based biosensors and venous plasma glucose measured with a chemistry analyzer. Biosensor test strips were used with a handheld glucose monitoring system. Bench and clinical oxygen sensitivity, hematocrit effect, and precision were evaluated.The study was performed at eight U.S. medical centers and one Canadian medical center.There were 1,248 patients.The GO-based biosensor was oxygen-sensitive. The new GD-based biosensor was oxygen-insensitive. GD-based biosensor performance was acceptable: 2,104 (96.1%) of 2,189 glucose meter measurements were within +/-15 mg/dL (+/-0.83 mmol/L) for glucose levels ofor = 100 mg/dL (or = 5.55 mmol/L) or within +/-15% for glucose levels of100 mg/dL, compared with the whole-blood reference method results. With the GD-based biosensor, the percentages of glucose measurements that were not within the error tolerance were comparable for different specimen types and clinical groups. Bracket predictive values were acceptable for glucose levels used in therapeutic management.The performance of GD-based, oxygen-insensitive, handheld glucose testing was technically suitable for arterial specimens in critical care patients, cord blood and heelstick specimens in neonates, and capillary and venous specimens in other patients. Multicenter findings benchmark the performance of bedside glucose testing devices. With the new +/-15 mg/dL --100 mg/dL --+/-15% accuracy criterion, point-of-care systems for handheld glucose testing should score 95% (or better), as compared with the recommended reference method. Physiologic changes, preanalytical factors, confounding variables, and treatment goals must be taken into consideration when interpreting glucose results, especially in critically ill patients, for whom arterial blood glucose measurements will reflect systemic glucose levels.

We evaluated whether arterial blood samples for pH and blood gas analysis need to be transported on ice. We found that although the changes in pH, pCO2 and pO2 were greater in samples kept at room temperature versus those kept on ice, the difference was probably not of clinical significance until the period of time after arterial puncture exceeded 20 minutes. We recommend that arterial blood samples do not need to be kept on ice if the analysis for pH and gases is performed within 20 minutes of blood being drawn.

SYNOPSIS. Phenylalanine hydroxylase could not be assayed in extracts of Tetrahymena pyriformis strain W in a system by which the enzyme could be assayed in rat liver extracts. Isotopically labelled phenylalanine, however, was converted to tyrosine by growing or washed cells. Growth conditions which allowed limited synthesis of unconjugated tetrahydropteridine severely reduced the ability of the cells to synthesize tyrosine from phenylalanine. The presence of glucose and acetate in the growth medium resulted in elevated free tyrosine pools and an increased capacity of washed cell suspensions to convert phenylalanine to tyrosine. It would appear that the putative phenylalanine hydroxylation system is not subject to the repressive effects of glucose and acetate which apply to the enzymes of tyrosine catabolism. The significance of this distinction is discussed.

We found total protein estimates in patients with monoclonal gammopathies to be erroneously low when using the Cobas-BioR centrifugal analyzer. This problem occurred only when a serum-water blank was used. This probably results from the precipitation of these proteins under conditions of low ionic strength resulting in high blank readings. The problem can be avoided if a serum-saline blank is used.

1. 1. A tyrosine-catabolizing system similar to that found in rat liver was found to be present in Tetrahymena pyriformis , strain W. The five constituent enzymes of the system, i.e. tyrosine aminotransferase, p -hydroxyphenylpyruvate oxidase, homogentisate oxidase, maleylacetoacetate isomerase and fumarylacetoacetate hydrolase were assayed in extracts of the cells. Fumarylacetoacetic acid was prepared enzymatically from homogentisic acid with a protein fraction of the cells. 2. 2. All the tyrosine-catabolizing enzymes and phosphoenolpyruvate (PEP) carboxykinase were repressed by glucose and by acetate. The first enzyme of the catabolic sequence, tyrosine aminotransferase, and PEP carboxylase were repressed by glucose in both logarithmic and stationary phases of growth while the four subsequenct catabolis enzymes were repressed essentially only in stationary phase. A close metabolis relationship was found to exist between tyrosine aminotransferase and PEP carboxykinase. 3. 3. The repression of enzymes by glucose and acetate was accompanied by a repression of carbon flow from tyrosine to glycogen. 4. 4. An inverse relationship exists between the activities of tyrosine aminotransferase and PEP carboxykinase on the one hand and isocitrate lyase on the other. This relationship and the repression of the catabolic enzymes by acetate, a glucogenic precursor in Tetrahymena , suggests that the regulation of the tyrosine-catabolizing enzymes and particularly of tyrosine aminotransferase is geared to the demand for gluconeogenesis from tyrosine in these cells.

A very significant effort in terms of dollars and man hours (up to 40% of workload) is spent on providing effective quality control in the chemistry laboratory. An important factor in quality of performance which is intuitively obvious but not readily quantitated is technologist workload. We have been able to significantly correlate (P less than 0.01) over a period of 4 years, performance in an external proficiency survey with technologist workload. Not surprisingly, the data suggests that the quality of test results diminishes as workload increases. The management strategy should then be directed towards decreasing workload possibly through appropriate automation.