Showing papers on "Glucose Measurement published in 1996"

Blood glucose strip having reduced sensitivity to hematocrit

Abstract: A reagent strip for measuring glucose concentration in whole blood has reduced interference of hematocrit with the glucose measurement. When a biological fluid contacts the strip, it causes, in a reagent impregnated in the strip, a color change that is a measure of the glucose concentration in the fluid. However, the color change is also affected by the red blood cell concentration (hematocrit), thereby reducing the accuracy of the glucose measurement. The hematocrit effect is reduced by adding to the reagent an acrylic acid polymer.

In Vivo Brain Glucose Measurements: Differential Normal Pulse Voltammetry with Enzyme-Modified Carbon Fiber Microelectrodes

Abstract: The enzyme glucose oxidase was immobilized on the surface of carbon fiber microelectrodes (CFMEs) either by cross-linking in glutaraldehyde vapor or by enzyme entrapment in electropolymerized films of m-phenylenediamine or resorcinol. The cross-linked enzymatic layer was, in the given conditions, covered with an additional membrane of Nafion or cellulose acetate. The prepared glucose sensors were tested using differential normal pulse voltammetry (DNPV, in which the scan comprises successive double pulses (“prepulse and pulse”), the prepulses are of increasing amplitude, and the current measured is the differential of the current existing between each prepulse and pulse). With properly chosen DNPV parameters, the response to glucose presented a peak at a potential of about 1 V versus an Ag/AgCl reference, owing to the oxidation of enzymatically produced hydrogen peroxide. The calibration curves obtained (peak height/glucose concentration) were linear from 0.3−0.5 up to 1.5−6.5 mM and showed a sensitivity ...

Comparison of hyperinsulinaemic clamp experiments using venous, ‘arterialized’ venous or capillary euglycaemia

Abstract: It has been suggested that deviations from arterial euglycaemia during hyperinsulinaemic clamp experiments that use venous plasma glucose measurements may alter the results of such tests (glucose infusion rate, C-peptide suppression, etc.) and that 'arterialized' venous blood ('heated-hand' technique) may be suitable to circumvent these problems. Therefore, nine normal male fasting volunteers (age 25 +/- 4 years, body mass index 23.5 +/- 2.3 kg m-2) were examined three times using an insulin infusion of 1 mU kg min-1 over 120 min. Glucose was infused to maintain a concentration of 4.7 mmol I-1 (85 mg dl-1) in venous (V), 'arterialized' venous ('heated-hand' technique; HH), or capillary (C) plasma. The 'heated-hand' technique caused a rise in (rectal) body temperature of 0.3 +/- 0.1 degree C (P < 0.0001). Whereas the glucose aim was reached to a similar degree in all experiments (P = 0.36), capillary glucose concentrations differed slightly, but significantly (higher in experiments with venous and 'arterialized' venous blood specimens; P = 0.034). There were no significant differences regarding steady-state insulin concentrations (P = 0.77), glucose infusion rates (V, 7.1 +/- 0.5; HH, 7.2 +/- 0.6; C, 6.4 +/- 0.5 mg kg-1 min-1; P = 0.98), C-peptide suppression (P = 0.78), reduction in glucagon (P = 0.27) and free fatty acids (P = 0.16), and all parameters of indirect calorimetry (non-protein RQ: P = 0.67; glucose and lipid oxidation: P = 0.72 and 0.46 respectively; and energy expenditure: P = 0.42). Therefore, hyperinsulinaemic clamp experiments performed using venous, 'arterialized' venous, or capillary euglycaemia appear to be almost equally useful for the determination of insulin sensitivity and C-peptide or glucagon suppression. The elevation in body temperature that accompanies use of the 'heated-hand' technique does not noticeably influence measured metabolic parameters.

Measuring blood glucose in neonatal units: how does hemocue compare?

Abstract: Rapid and reliable determination of blood glucose concentration is essential during the neonatal period to prevent adverse neurodevelopmental outcome from hypoglycaemia. Despite their unreliability, reagent strip methods continue to be used extensively in neonatal nurseries due to their rapidity and convenience. Recently, a new portable laboratory standard technique has been introduced (HemoCue B-Glucose system) for whole blood glucose determination. It is particularly suitable for near-patient testing in neonatal units. This new method, as well as other established methods of whole blood (Yellow Springs Instrument (YSI) and a hexokinase method on Cobas Bio), and plasma (Kodak Ektachem) glucose measurement, were therefore evaluated for their accuracy and concordance of measurements taken in the neonatal period. There were substantial discrepancies among the four methods of glucose measurement with wide limits of agreement between these methods. The glucose concentrations measured by HemoCue and YSI (n = 206), HemoCue and hexokinase (n = 113), HemoCue and plasma glucose on Ektachem (n = 69) and hexokinase and Ektachem (n = 66) were likely to differ by -29 to +61%, -23 to +56%, -36 to +65%, and -19 to +30%, respectively. Even the laboratory methods of blood glucose determination, therefore, can not be used interchangeably. Using a model based approach, the probabilities of "discordant" classification as hypo- or normo-glycaemia were estimated to be 6.8%, 6.5%, and 7.1% between HemoCue and YSI, HemoCue and hexokinase on Cobas Bio, and HemoCue and Ektachem analysers, respectively. In view of these low probabilities of discordant classification with other glucose analysers, the HemoCue system may offer a reasonable compromise between bedside and laboratory blood glucose estimations in neonates.

Laboratory diagnosis of insulinoma in the dog: A retrospective study and a new diagnostic procedure

Abstract: Simultaneous insulin and glucose measurements from a single sample are often insufficient for the laboratory diagnosis of insulinoma in the hypoglycaemic dog. Although the simple insulin (microU/litre): glucose (mmol/litre) ratio is best, when the selected threshold is set at 13.5, it is not always efficient to confirm or refute insulinoma. The fasting test consists of collecting four samples on a given day (no accurate time period is set between any two samples) from a fasting dog for simultaneous insulin and glucose measurements to detect at least one abnormal insulinaemia peak.

Assessment of a critical limit protocol for point-of-care glucose testing.

Abstract: A critical limit protocol requiring that all point of care glucose meter readings > 22.2 mmol/L (400 mg/dL) and 22.2 or 50% discordance between glucose meter/central lab with three (27%) glucose meter errors, emphasizing the need to confirm critically high/low glucose meter results to avoid potential errors. The critical limit protocol now requires that only the initial critically high/low glucose meter reading be confirmed by the lab and that these patients now be followed with lab values until glucose levels are between 5.6-16.7 mmol/L (100-300 mg/dL) before the glucose meter can again be used.

Current Status of the Glucose Sensor

Abstract: This study gives an overview of glucose sensing strategies for potential use in diabetes therapy. The basis for the most commonly used amperometric glucosensors is the Clark electrode which measures oxygen tension. Coupling this sensor with glucose oxidase led to the first specific “biosensor” for glucose measurement. This sensor has been used for more than 20 years in the in vitro artificial pancreas (“Biostator”). The development of implantable glucose sensors has been hampered by the disappointing in vivo behavior of these sensors. Alternative glucose sensing techniques including noninvasive approaches are still experimental. Combining the microdialysis technique for continuous sampling of subcutaneous extra-cellular fluid with an in vitro on-line amperometric glucose oxidase electrode (the “Ulmer Zuckeruhr” or “sugar watch” system), permits continuous glucose sensing for 72 hours. Although there are differences and delays between changes in tissue and blood glucose concentrations, a complete automated feedback-controlled insulin delivery system is possible if fast acting insulin analogs can close the insulin delivery “feedback loop.”

Effects of pressure on whole blood glucose measurements using the Bayer Glucometer 4 blood glucose meter.

Abstract: The effect of pressure was investigated on the readings of whole blood glucose obtained from the Bayer Glucometer 4 blood glucose meter which uses the hexokinase enzymatic reaction. Sixteen subjects (eight normal and eight insulin-dependent diabetics) were exercised in a hyperbaric chamber at a depth of 3.7 atm abs. Venous blood samples were monitored at regular intervals for whole blood glucose concentration as measured by a Glucometer 4 inside the chamber. The blood samples were immediately placed in an airlock and taken to 1 atm abs, where whole blood glucose concentrations were measured using an identical instrument. The remaining blood was then analyzed in duplicate for serum glucose concentration using standard laboratory methods. The results show a significant difference between whole blood glucose concentrations measured at pressure and those measured at atmospheric pressure. Significant differences are also observed between whole blood glucose concentrations measured under pressure and serum blood glucose concentrations measured at atmospheric pressure.

Glucose as an adjunct triage tool to the Red Cross Wound Classification.

Abstract: The plasma concentrations of glucose, adrenaline, noradrenaline, insulin, and cortisol were measured in 59 patients within 18 hours of military gunshot/missile (MG/M) wound. The wounds were categorized by the Red Cross Wound Classification (RCWC) and assessed by the Injury Severity Score (ISS) method. The majority of the measured biochemical parameters, except insulin, were significantly increased after MG/M wounds, compared with control values. Plasma glucose concentration in wounded patients was positively related to ISS over the whole severity range. Plasma insulin eoncentration increased with glucose. Noradrenaline and cortisol were positively related to glucose. Because hemorrhage is the most common cause of general response to MG/M wound, we concluded that glucose measurement could be a useful adjunct tool to the RCWC in rapid and accurate assessment of severely wounded patients, especially those with occult thoraco-abdominal wounds.

Effect of physiological factors and other analytes on the determination of glucose concentration in vivo by optical absorption and scattering meaurements

Abstract: Determining the concentration of glucose in vivo by near-infrared spectroscopy is complicated by the effects of optical changes caused by fluctuations in temperature, tissue water content and the concentration of other analytes. Mie theory and Monte Carlo computer simulation of light transport in optically absorbing and scattering media were used to investigate the magnitude of the changes in diffuse reflectance and transmittance from changes in glucose. Similarly, the possible interference in the glucose measurement from the other tissue parameters have been assessed and found to be significant.

The metabolic assessment of patients with diabetes mellitus

Abstract: This thesis critically evaluates two developments which have both brought about major advances in the assessment of glycaemic control in diabetic patients. First is the measurement of glycated proteins in the form of glycated haemoglobin and serum fructosamine and the second is the use of portable test strips and meters for the self-monitoring of blood glucose. Both methods of assessment have gained widespread acceptance but there remains a number of clinical and methodological problems associated with their use. This thesis reviews the literature relating to the use of these tests and describes a number of studies demonstrating new benefits and difficulties which exist. The majority of clinicians now use glycated haemoglobin measurement as their principal objective indicator of glycaemic control in diabetic patients. We have performed several detailed studies elucidating clinically relevant aspects of glycated haemoglobin measurement which can affect the assessment of glycaemia in these patients. The setting of target values for glycated haemoglobin measurement is severely hindered by the lack of standardisation in methodology. In an attempt to account for this, European guidelines define categories of glycaemic control as an HbA1 or HbA1c concentration so many standard deviations from a particular method's non-diabetic population mean. Using these guidelines, we found that HbA1 could classify the same diabetic patients differently to HbA1c, even when using the same instrument and reference range individuals. This new finding led, in part, to a change in the European guidelines for glycated haemoglobin targets. Many commonly used glycated haemoglobin methods include both glycated and non-glycated fetal haemoglobin (HbF) in their result. This means patients with elevated HbF concentrations (>0.5%) can have spuriously high glycated haemoglobin values. We presented the first evidence that insulin treated adult patients had a significantly greater prevalence of elevated HbF concentrations than either non-insulin treated or non-diabetic controls, thereby compounding the problem in this group of patients. In addition, we found that HbF increased the apparent imprecision of these assays. Discrepancies exist when comparing glycated haemoglobin and serum fructosamine as indicators of glycaemic control. We found that in newly diagnosed Type II diabetes, fructosamine only showed a correlation with HbA1 after glucose control had stabilised and not during the period of changing glycaemia. However, because changes in fructosamine preceded those of HbA1, the ratio of fructosamine/ HbA1 was able to predict the change in HbA1 in the forthcoming month. Thus, parallel measurement of fructosamine with HbA1 provided additional information on the future trend of a HbA1concentration. A further reason for disparity between fructosamine and glycated haemoglobin was established when investigating the effects of ageing on glycation in non-diabetic subjects. Mean HbA1 values rose with increasing subject age while fructosamine and fasting plasma glucose values did not. Consequently, when Type II diabetic patient samples were classified according to European HbA1 guidelines, significantly fewer patients were in good control and more in poor control when a young reference population was used compared to an age matched one. Thus, age related reference intervals may be required for glycated haemoglobin measurement. Using test strips and meters to measure blood glucose has become widespread amongst diabetic patients in the community and in the monitoring of acutely ill hospital patients. We have documented studies which describe the effect on glucose measurement of variations in several physiological parameters. We also describe how new technology is improving glucose meter measurement. In vitro variations of sample haematocrit have been shown to be a source of error in several glucose meter systems. Red cell count and mean cell volume are intimately related to haematocrit, so it makes it impossible to distinguish if the test strip error is due to haematocrit variations per se or to changes in the number of red cells. We found that in groups of individuals with different mean cell volumes, meter error was still related to the haematocrit of the sample rather than its red cell count. Having established this, 10 patients undergoing cardiopulmonary bypass (whose haematocrits routinely fall to 20% intraoperatively) were investigated to determine the effect of in vivo variations in haematocrit. Changes in test strip glucose accuracy were found to be consistent with those shown previously in vitro. While the use of whole blood to measure glucose is convenient, it is not possible, unlike plasma or serum, to tell if a sample is in any way haemolysed. We showed that extreme sample haemolysis can affect several glucose meter systems, while even modest degrees of red cell lysis were found to give clinically inaccurate results when using the Accutrend instrument. (Abstract shortened by ProQuest.).