Abstract
BackgroundThe diagnosis of hyperglycaemia in sub-Saharan Africa (SSA) is challenging. Blood glucose levels obtained during oral glucose tolerance test (OGTT) may not reflect home glycaemic profiles. We compare OGTT results with home glycaemic profiles obtained using the FreeStyle Libre continuous glucose monitoring device (FSL-CGM).MethodsTwenty-eight women (20 with gestational diabetes [GDM], 8 controls) were recruited following OGTT between 24 and 28 weeks of gestation. All women wore the FSL-CGM device for 48–96 h at home in early third trimester, and recorded a meal diary. OGTT was repeated on the final day of FSL-CGM recording. OGTT results were compared with ambulatory glycaemic variables, and repeat OGTT was undertaken whilst wearing FSL-CGM to determine accuracy of the device.ResultsFSL-CGM results were available for 27/28 women with mean data capture 92.8%. There were significant differences in the ambulatory fasting, post-prandial peaks, and mean glucose between controls in whom both primary and secondary OGTT was normal (n = 6) and those with two abnormal OGTTs or “true” GDM (n = 7). There was no difference in ambulatory mean glucose between these controls and the 13 women who had an abnormal primary OGTT and normal repeat OGTT. These participants had significantly lower body mass index (BMI) than the true GDM group (29.0 Vs 36.3 kg/m2, p-value 0.014).Paired OGTT/FSL-CGM readings revealed a Mean Absolute difference (MAD) -0.58 mmol/L and Mean Absolute Relative Difference (MARD) -11.9%. Bland-Altman plot suggests FSL-CGM underestimated blood glucose by approximately 0.78 mmol/L.ConclusionDiagnosis of GDM on a single OGTT identifies a proportion of women who do not have a significantly higher home glucose levels than controls. This raises questions about factors which may affect the reproducibility of OGTT in this population, including food insecurity and atypical phenotypes of diabetes. More investigation is needed to understand the suitability of the OGTT as a diagnostic test in sub-Saharan Africa.
Highlights
The diagnosis of hyperglycaemia in sub-Saharan Africa (SSA) is challenging
Diagnosis of Gestational diabetes (GDM) on a single oral glucose tolerance test (OGTT) identifies a proportion of women who do not have a significantly higher home glucose levels than controls
This raises questions about factors which may affect the reproducibility of OGTT in this population, including food insecurity and atypical phenotypes of diabetes
Summary
The diagnosis of hyperglycaemia in sub-Saharan Africa (SSA) is challenging. Blood glucose levels obtained during oral glucose tolerance test (OGTT) may not reflect home glycaemic profiles. Our recent study in urban and peri-urban central Uganda supports this (Natamba B, unpublished) These prevalence estimations are made using the WHO 2013 guidelines which recommend the following criteria for making a diagnosis of hyperglycaemia in pregnancy using the 2-h oral glucose tolerance test (OGTT); fasting ≥5.1 and 2-h ≥ 8.5 mmol/ L for gestational diabetes (GDM), and ≥ 7.0 and 2-h ≥ 11.1 mmol/L for diabetes in pregnancy (DIP) [2]. These strict glycaemic cut-offs were extrapolated from the multinational HAPO study which did not include women in Africa and has not been validated in the sub-Saharan African setting [3]. Physical exertion to reach antenatal clinic, which may reduce fasting glucose results, is common
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