<p>The Oral Glucose Tolerance Test: 100 Years Later</p>

Abstract

For over 100 years, the oral glucose tolerance test (OGTT) has been the cornerstone for detecting prediabetes and type 2 diabetes (T2DM). In recent decades, controversies have arisen identifying internationally acceptable cut points using fasting plasma glucose (FPG), 2-h post-load glucose (2-h PG), and/or HbA1c for defining intermediate hyperglycemia (prediabetes). Despite this, there has been a steadfast global consensus of the 2-h PG for defining dysglycemic states during the OGTT. This article reviews the history of the OGTT and recent advances in its application, including the glucose challenge test and mathematical modeling for determining the shape of the glucose curve. Pitfalls of the FPG, 2-h PG during the OGTT, and HbA1c are considered as well. Finally, the associations between the 30-minute and 1-hour plasma glucose (1-h PG) levels derived from the OGTT and incidence of diabetes and its complications will be reviewed. The considerable evidence base supports modifying current screening and diagnostic recommendations with the use of the 1-h PG. Measurement of the 1-h PG level could increase the likelihood of identifying high-risk individuals when the pancreatic ß-cell function is substantially more intact with the added practical advantage of potentially replacing the conventional 2-h OGTT making it more acceptable in the clinical setting.

Carbohydrate Intake Prior to Oral Glucose Tolerance Testing

“…The utility of HbA1c is unassailable, but like every test, it has flaws [ 38 ]. A threshold of HbA1c >6.5% was suggested for the diagnosis of diabetes based on studies demonstrating an association between HbA1c and diabetic retinopathy, but data suggest that this HbA1c level fails to identify a significant population of people with diabetes by OGTT or fasting PG [ 39 , 40 ]. AACE/ACE and ADA guidelines acknowledge limitations in HbA1c and fasting PG as tools for diagnosis of diabetes, implying that measuring PG after a 75-gram 2-hour OGTT may be the most sensitive test for detecting diabetes [ 1 , 5 ].…”

Reply to: “The predictive value of significant fibrosis for metabolic disturbances in patients with NAFLD”

“…Although the histological features of NAFLD were first described decades ago, Klatskin and his colleagues, in 1979, were the first to use the term 'non-alcoholic liver disease'. 3 Later, while reporting similar findings, Ludwig and colleagues coined the term "non-alcoholic steatohepatitis (NASH)".…”

“…However, these tests, such as oral glucose tolerance test, are not suitable for a wide screening of patients because they are time-consuming (2 hours duration) and not cost-effective in this scenario. 3 Further, these tests are typically carried out in dedicated units, such as Endocrinology units. Additionally, the authors mention the possibility of including LDL-cholesterol (LDL-c) to evaluate dyslipidemia due to its relationship with cardiovascular diseases.…”

Oral glucose tolerance test in diabetes, the old method revisited

“…The OGTT was standardized by establishing an oral glucose load of 75 g and 2-h post-glucose load glycemia (2hPG), according to the Expert Committee of the American Diabetes Association (ADA)[ 12 ]. Overnight fasting glucose (FPG) and impaired fasting glycemia (IFG) were also recommended by the ADA.…”