The oral glucose tolerance test--an assessment of the quality of its performance

Are all glucose solutions used for oGTT equal?

AIMS

Oral glucose tolerance tests (oGTT) are widely used for the diagnosis of diabetes. It is well known that the reproducibility of oGTT is poor and that a number of factors have an impact on the outcome of this diagnostic test. It appears as if one aspect, the oral glucose solution (OGS) used has not achieved much attention. Very little is published about this, despite the fact that apparently most often not a pure and freshly prepared glucose solution is used but a ready-to-use solution prepared by a (pharmaceutical) company.

METHODS

A literature search was performed to find respective publications.

RESULTS

It appears as if no or only a small number of not adequately designed clinical-experimental studies have been performed comparing different OGS head-to-head.

CONCLUSIONS

The composition of such OGS, including the excipients added to improve taste and smell, can have an impact on blood glucose increase after drinking the given OGS. Such factors can also have an impact on endogenous insulin secretion. If significant differences in the blood glucose excursions exist depending on which OGS is used, this calls for the use of a standardized OGS in oGTT to have a comparable outcome everywhere.

A multicentre study to investigate the prevalence of abnormal carbohydrate metabolism in Chinese pregnant women

OBJECTIVES

To determine the prevalence of abnormal carbohydrate metabolism in Chinese pregnant women. To study the inter-relationship between maternal body habitus, maternal serum glucose and birth weight of the baby.

METHODS

Multicentre observational study involving 713 pregnant Chinese women, attending antenatal clinics in Beijing, Shanghai, Guangzhou and Hong Kong.

RESULTS AND CONCLUSION

The overall prevalence of abnormal glucose tolerance was 6.9%. The prevalence was 6.8%, 5.5%, 7.2% and 8.1% in Beijing, Shanghai, Guangzhou and Hong Kong, respectively. The differences among the centres did not reach statistical significance (p = 0.9). The mean ponderal index of women with abnormal glucose tolerance was significantly higher than that of women with normal glucose tolerance (15.2 vs 14.3, p < 0.01). The birth weight ratio of the babies was positively correlated with the maternal height (correlation coefficient 0.23, 95% C.I. 0.15-0.30), weight (0.32, 95% C.I. 0.25-0.39) and to a lesser extent, the fasting level of serum glucose (0.10, 95% C.I. 0.02-0.28) but not with the 2 hour level of serum glucose.

Influence of sample type on the interpretation of the oral glucose tolerance test for gestational diabetes mellitus

The World Health Organization (1985) criteria allow evaluation of the oral glucose tolerance test using venous or capillary whole blood or plasma glucose measurements. However, the empirical factors used for interconversion may not reflect observed differences, especially during pregnancy, causing inconsistent classification. To investigate how choice of sample would influence the interpretation of results, venous and capillary blood was taken during oral glucose tolerance tests in 36 pregnant women at risk of gestational diabetes and in 21 non-pregnant control subjects. Glucose was measured on whole blood and plasma by a glucose oxidase method. No cases of gestational diabetes were identified. Eight subjects had gestational Impaired Glucose Tolerance using either venous plasma or venous whole blood results, but only five were similarly classified with capillary whole blood and only four using capillary plasma. Plasma-whole blood differences (venous 0.6 +/- 0.2 (+/- SD) mmol l-1, capillary 0.7 +/- 0.3 mmol l-1) and capillary-venous differences (plasma 0.5 +/- 0.4, whole blood 0.4 +/- 0.5 mmol l-1) at 2 h were lower (all p less than 0.05) than in the WHO criteria (1.1 mmol l-1). When compared with venous plasma, capillary measurements may give a lower incidence and venous whole blood measurements a higher incidence of Impaired Glucose Tolerance in pregnancy.

Variability of capillary plasma glucose in healthy individuals in repeated 75 g oral glucose tolerance tests

A series of ten 75 g oral glucose tolerance tests was carried out on each of 14 apparently healthy subjects. The analytical, intra-individual and interindividual components of variation were calculated by nested ANOVA following duplicate analyses of capillary plasma glucose under optimal conditions. The analyses met the objectively set analytical goal of CV less than or equal to 2.2%. There was considerable intra-individual variation, but no subject was ever classified as diabetic or having impaired glucose tolerance. Recent criteria for interpretation of results must be used since conventional population-based reference values are not adequate. Serial results from an individual must differ by more than 0.7 mmol/L for fasting specimens and at least 1.6 mmol/L for other specimens for a statistically significant (P less than or equal to 0.05) change to have occurred.