Capillary glucose determination in the screening of gestational diabetes

Paired capillary-venous blood samples were obtained from 418 pregnant women undergoing an oral glucose challenge test (GCT) for the screening of gestational diabetes (GD). The relationship between capillary and plasma glucose concentrations was investigated in order to establish a capillary GCT threshold. Plasma glucose was assayed by the glucose oxidase method and capillary glucose using Reflocheck Glucose strips and a Reflocheck reflectance meter. During GCT the capillary values exceeded plasma glucose values by a mean difference of 10-12 mg/dl fasting and 22-24 mg/dl after 1 h. A high correlation between the glucose values of the two techniques was found, particularly for those at 1 h, with corresponding capillary determinations being 20 mg/dl above plasma values. The sensitivity, specificity and predictive value of the various capillary thresholds investigated in detecting GD corresponded substantially to the accuracy of plasma thresholds 20 mg/dl lower. The receiver operator characteristic curves of the plasma and capillary thresholds were similar in shape and the optimal cut-off point for performing a diagnostic test was set at 135 and 155 mg/dl, respectively. These cut-off values should be reconsidered in the light of the costs and perinatal outcome.