Impact of Glucose Measuring Systems and Sample Type on Diagnosis Rates of Diabetes Mellitus

Abstract

Introduction

The use of glucose point-of-care testing (POCT) devices for the diagnosis of diabetes mellitus (DM) is an ongoing controversy. In patient management, glucose concentrations are determined by POCT and core laboratory glucose methods, and the values are commonly compared even though the samples collected are different, namely, capillary whole blood and venous plasma. In individual patients it is difficult to distinguish between factors that can influence the results, such as sample type and measuring procedure. In this study, glucose concentrations obtained using POCT and core laboratory instruments were assessed to duplicate typical scenarios experienced in healthcare. Corresponding diagnosis rates of impaired glucose tolerance (IGT) and DM based on fixed, method-independent cutoffs were compared.

Methods

Glucose concentration was measured by the 2-h oral glucose tolerance test (OGTT) in samples collected from an inpatient cohort and a cohort from the general population. Two POCT methods, namely, a handheld unit-use glucometer and a small bench-top analyzer with batch reagents, and two core laboratory procedures were used to measure glucose concentrations. The sample types were whole blood and plasma samples collected from venous and capillary blood. The glycated hemoglobin level in whole blood was also determined.

Results

A total of 231 subjects were included in the study. The 2-h OGTT glucose concentrations in the capillary whole blood samples showed a positive bias of 0.8 mmol/L compared to those obtained using core laboratory plasma glucose methods, leading to increased rates of diabetes diagnosis. This bias decreased to 0.2 mmol/L when venous blood was used in the tests. A change in the method used by the core laboratory introduced a negative bias of 0.5 mmol/L and, consequently, a lower diagnosis rates.

Discussion and Conclusion

Venous blood samples measured at the point-of-care are the most suitable sample type for the measurement of the glucose concentration in the 2-h OGTT. The investigated unit-use POCT method is suitable for the diagnosis of IGT and DM when venous blood samples are collected. Importantly, changes in measurement procedures can introduce a bias and affect diagnosis rates, thereby emphasizing the need for further harmonization of glucose methods.

Plain Language Summary

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Plain Language Summary

In clinical practice, a physician may be confronted with blood glucose concentrations determined using different devices. It is difficult for the treating physician to assess the effect of factors that can impact the glucose measurement, such as sample type and measuring procedure, for a given glucose concentration result. The aim of this study was to duplicate typical scenarios in the healthcare setting in terms of differences in glucose concentrations in capillary and venous samples obtained using a handheld point-of-care testing device, one benchtop device, and two core laboratory instruments. The diagnosis rates of impaired glucose tolerance and diabetes mellitus were compared to demonstrate the effects of the glucose concentrations measured using these different devices in terms of clinical response. We performed an oral glucose tolerance test and obtained the blood glucose concentration immediately before and 2 h after an oral glucose load. The results were compared and presented using difference and scatter plots. A total of 231 subjects were included in the study. Glucose concentrations in capillary whole blood samples showed a positive bias compared to those determined using core laboratory methods, leading to increased rates of diabetes diagnosis. This bias decreased when venous whole blood samples were used. A change in the method used in the core laboratory introduced a negative bias and, consequently, lower diagnosis rates. Changing laboratory devices can introduce a bias that is sufficiently large as to affect the diagnosis of diabetes since the latter is based on method-independent cutoffs. From these findings we conclude that both of the point-of-care devices investigated are suitable for the diagnosis of diabetes when venous samples are used. Our findings also emphasize the need for further harmonization of the glucose testing method.