Point-of-care glucose analysis in neonates using modified quinoprotein glucose dehydrogenase.

BACKGROUND: Asymptomatic hypoglycemia in neonates may contribute to neurologic deficits during development. Whole-blood glucose sensors are often imprecise and inaccurate at the low glucose concentrations found in neonates. SUBJECTS AND METHODS: In this study, a glucose sensor using a mutated glucose dehydrogenase that does not cross-react significantly with maltose was evaluated at three pediatric centers. Blood samples (n=575) from infants less than 30 days of age (hematocrit 23-70%) were analyzed using six reagent lots on three ACCU-CHEK(®) meters (Roche Diagnostics, Indianapolis, IN): the Inform II, Performa, and Aviva. Reference glucose level was determined in duplicate in perchloric acid extracts using a coupled hexokinase procedure. RESULTS: Imprecision of glucose measurement using stable control materials ranged from 2.0% to 3.1% (coefficient of variation) using the glucose meters and from 0.8% to 5.3% (coefficient of variation) in perchloric acid-treated controls. The difference between meter glucose values and reference values showed a slight dependence on hematocrit from 23% to 70% (r=-0.391, P<0.001) but not in the typical range of neonatal hematocrit from 45% to 70% (r=-0.036, P=0.239). Linear regression of the aggregated results yielded the following relationship: Meter glucose=0.99×Reference Glucose+0.04; r(2)=0.976; Syx=0.249. Receiver-operator characteristic analysis of the data using 2.2 mmol/L as the reference threshold for hypoglycemia yielded an area under the curve value of 0.993. All infants with a glucose level of <2.2 mmol/L were detected (100% sensitivity) when the meter glucose value was below 2.8 mmol/L. CONCLUSIONS: These data indicate that the modified ACCU-CHEK chemistry may be used effectively in neonatal settings to detect clinically significant hypoglycemia.

Oxygen effects on glucose meter measurements with glucose dehydrogenase- and oxidase-based test strips for point-of-care testing.

OBJECTIVES: To determine the effects of different oxygen tensions (Po2) on glucose measurements with glucose dehydrogenase (GD)-based and glucose oxidase (GO)-based test strips, to quantitate changes in glucose measurements observed with different Po2 levels, and to discuss the potential risks of oxygen-derived glucose errors in critical care. DESIGN: Venous blood from healthy volunteers was tonometered to create different oxygen tensions simulating patient arterial Po2 levels. Venous blood from diabetic patients was exposed to air to alter oxygen tensions simulating changes in Po2 during sample handling. Whole-blood glucose measurements obtained from these samples with six glucose meters were compared with reference analyzer plasma glucose measurements. Glucose differences were plotted vs. different Po2 levels to identify error trends. Error tolerances were as follows: a) within +/-15 mg/dL of the reference measurement for glucose levels 100 mg/dL. SETTING AND SUBJECTS: Five healthy volunteers in the bench study and 11 diabetic patients in the clinical study. RESULTS: In the bench study, increases in Po2 levels decreased glucose measured with GO-based amperometric test strips, mainly at Po2 levels >100 torr. At nearly constant glucose concentrations, glucose meter systems showed large variations at low (39 torr) vs. high (396 torr) Po2 levels. Glucose measured with GD-based amperometric and GO-based photometric test strips generally were within error tolerances. In the clinical study, 31.6% (Precision PCx), 20.2% (Precision QID), and 23.0% (Glucometer Elite) of glucose measurements with GO-based amperometric test strips, 14.3% (SureStep) of glucose measurements with GO-based photometric test strips, and 4.6% (Accu-Chek Advantage H) and 5.9% (Accu-Chek Comfort Curve) of glucose measurements with GD-based amperometric test strips were out of the error tolerances. CONCLUSIONS: Different oxygen tensions do not significantly affect glucose measured with the GD-based amperometric test strips, and have minimal effect on GO-based photometric test strips. Increases in oxygen tension lowered glucose measured with GO-based amperometric test strips. We recommend that the effects of different oxygen tensions in blood samples on glucose measurements be minimized by using oxygen-independent test strips for point-of-care glucose testing in critically ill and other patients with high or unpredictable blood Po2 levels.

Glucose-6-phosphate dehydrogenase and gluta thione reductase activity in methemoglobin reduction by methylene blue and cystamine: study on glucose-6-phosphate dehydrogenase-deficiente individuals on normal subjects and on riboflavin

Os autores padronizaram métodos para a avaliaçäo da atividade da glicose-6-fosfato desidrogenase e glutationa redutase. O princípio geral do primeiro método baseou-se na formaçäo de metahemoglobina pelo nitrito de sódio, seguido da estimulaçäo da via das pentoses pelo azul de metileno. Foram estudados 46 indivíduos adultos, sendo 23 do sexo masculino e 23 do feminino, näo deficientes em glicose-6-fosfato desidrogenase (G6PD), com idades variando entre 20 e 30 anos. Os resultados revelaram que a reduçäo da metahemoglobina pelo azul de metileno para sangue total, foram de 154.50 e 139.90 microng/min (p<0.05) respectivamente para o sexo masculino e feminino. Para hemácias lavadas os valores foram de 221.10 e 207.85 microng/min(n.s.) respectivamente. Estas observaçöes permitiram concluir que ao se empregar hemácias lavadas e 0.7 g% de concentraçäo de nitrito de sódio, por um lado näo houve diferença entre os sexos e por outro, abreviou o tempo de leitura da quantidade residual de metahemoglobina para 90 minutos. A avaliaçao da atividade da glutationa redutase foi feita baseado no fato de que a cistamina (agente tiol) liga-se aos grupo SH da hemoglobina formando complexos. Estes complexos säo revertidos pela açäo da glutationa redutase, ocorrendo conjuntamente nesta reaçäo a reduçäo da metahemoglobina. Foram estudados 32 indivíduos adultos, sendo 16 do sexo masculino e 16 do feminino, näo deficientes em G6PD, com idades variando entre 20 e 30 anos