New test to detect future risk of type 2 diabetes

Study reveals one-hour glucose >155 after 75 g OGTT means prediabetes

The one-hour glucose level during an oral glucose-tolerance test (OGTT) improves the early prediction of type 2 diabetes, according to results from the Botnia Prospective Study.

In the study, 1-hour plasma glucose (PG) alone was almost as good as most other multivariate models, especially the combination of HbA1c and 1-hour PG, in predicting type 2 diabetes.

One-hour plasma glucose showed the best predictive performance for type 2 diabetes, with 75 per cent sensitivity, 68 per cent specificity and 75 per cent accuracy (by AUC), followed by the 30-min plasma glucose, with 62 per cent sensitivity, 71 per cent specificity and 71 per cent accuracy. Both measures were more accurate than fasting plasma glucose or two-hour plasma glucose.

These results are reported online November 15, 2018 in the Journal of Clinical Endocrinology and Metabolism.
OGTT is a test commonly employed to screen for and diagnose type 2 diabetes and also to detect persons with prediabetes. It is an important risk factor for future type 2 diabetes. So, it is important to diagnose prediabetes early and also intervene early to prevent progression to type 2 diabetes.

Conventionally, the results at 2 hours are taken into consideration when determining the risk status of an individual, as has been recommended in guidelines. As per American Diabetes Association (ADA) with 2019 standards of medical care for diabetes, patients prediabetes are defined by the presence of IFG and/or IGT and/or A1C 5.7–6.4 per cent. IFG is defined as FPG levels between 100 and 125 mg/dL and IGT as 2-h PG during 75-g OGTT levels between 140 and 199 mg/dL).

But, this new study has shown that individuals with 1-hour blood glucose level >155 mg/dL have a very high risk of developing type 2 diabetes and should be subjected to adequate life-style intervention and follow-up.
According to International Diabetes Federation (IDF) Diabetes Atlas (7th Edition), India is second only to China in terms of the number of people with diabetes. China had the largest number of diabetes (11.43 crore) in 2017, while the corresponding number was 7.29 crore in India.

Identification of people at risk of type 2 diabetes at an even earlier time than what is routinely followed is the need of the hour to check the rising burden of type 2 diabetes in India.

An article in the December 2018 issue of Diabetes Research and Clinical Practice has strongly advocated redefining current diagnostic criteria for prediabetes with the elevated 1-h blood glucose level (Diabetes Res Clin Pract. 2018 Dec;146:18-33). It states: “The 1-hour postload blood glucose  ≥ 155 mg/dl in those with normal glucose tolerance (NGT) during OGTT is highly predictive for detecting progression to type 2 diabetes, micro- and macrovascular complications and mortality in individuals at increased risk.”

The STOP DIABETES Study also showed that progression to type 2 diabetes in people at high risk of diabetes – those with NGT and a 1-h PG ≥ 155 mg/dl (8·6 mmol/L) – can be reduced by effective interventions (Lancet Diabetes Endocrinol. 2018 Oct;6(10):781-9).

What these studies tell us is that shortening the standard 75-g OGTT to one hour improves the predictive value as well as clinical utility, especially in patients in whom the A1c, fasting blood sugar and the 2-hour OGTT are normal.