Multicenter study of oxygen-insensitive handheld glucose point-of-care testing in critical care/hospital/ambulatory patients in the United States and Canada.

OBJECTIVES: 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. DESIGN: 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. SETTING: The study was performed at eight U.S. medical centers and one Canadian medical center. PATIENTS: There were 1,248 patients. RESULTS: 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 of < or = 100 mg/dL (< or = 5.55 mmol/L) or within +/-15% for glucose levels of > 100 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. CONCLUSIONS: 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.

Managing bedside glucose testing in the hospital.

The scope and magnitude of bedside testing by personnel without formal laboratory training have recently increased. There has been some question about the reliability of bedside test results produced by nurses, physicians, and other ward staff that are used in clinical decisions. Glucose testing is currently the most widely performed bedside test. Because of the likelihood that the use of bedside testing will increase in the future, this article discusses various issues concerning bedside glucose analysis, including the scope of such testing, staff responsibilities, training and supervision, testing frequency, work flow and result reporting, and the reliability of bedside glucose results, in three institutions. We also suggest an approach to bedside testing quality management.

Spurious increase in serum creatinine associated with intravenous methyldopate therapy.

A patient with subarachnoid hemorrhage treated with intravenous methyldopate experienced a sudden marked increase in serum creatinine. This increase was due to interference by methyldopate in the assay for serum creatinine. By performing in vitro interference studies, we confirmed that methyldopate interferes with the creatinine assay.

Is it necessary to transport arterial blood samples on ice for pH and gas analysis?

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.

Artefactual decrease in total protein concentration in patients with monoclonal gammopathies: a method-dependent error.

We found total protein estimates in patients with monoclonal gammopathies to be erroneously low when using the Cobas-Bio 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.

Clinical utility of lactic acid measurement in body fluids other than plasma.

The diagnosis of septic infections of closed body cavities requires a careful search. Traditional laboratory tests such as Gram's stain, white cell count, and protein and glucose levels are often inconclusive. Measurement of lactic acid in cerebrospinal, synovial, pleural, ascitic, and bursal fluids has been utilized to distinguish bacterial from nonbacterial infections. The present review summarizes the current status of lactic acid measurement in the differential diagnosis of meningitis, arthritis, empyema, bacterial peritonitis, and bursitis.

Assessment of technologist workload as a factor in quality of laboratory performance.

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.

Maltotetraose as a substrate for enzyme-coupled assay of amylase activity in serum and urine.

The use of maltotetraose ss a new substrate for the enzyme-coupled determination of amylase activity in biological fluids was developed by Beckman Microbics. We evaluated a manual and a centrifugal analyzer version of the method in comparison with two commonly used manual starch-dye amylase techniques: Roche Amylochrome and Pharmacia Phadebas. Both maltotetraose amylase procedures proved to be rapid and precise, and results correlated satisfactorily with the starch-dye methods for serum and urine samples.

Regulation of acetohydroxy acid synthase in streptomycin-dependent Escherichia coli.

Growth of streptomycin-dependent mutants of Escherichia coli K-12 was insensitive to valine when dihydrostreptomycin was present in a nonlimiting concentration in glucose-salts medium. Acetohydroxy acid synthase was derepressed under these conditions, owing to relaxation of catabolite repression. Valine sensitivity and catabolite repression were restored when streptomycin-dependent E. coli K-12 mutants were grown with limiting dihydrostreptomycin. End product repression of acetohydroxy acid synthase under conditions of relaxed catabolite repression was effected by any two (or more) end products except the combination valine plus isoleucine, which caused derepression. Single end products had no detectable effect on acetohydroxy acid synthase formation.