Which test is more sensitive for diagnosing diabetes and impaired glucose tolerance but is less convenient and is rarely used routinely except for gestational diabetes and research?

Which test is more sensitive for diagnosing diabetes and impaired glucose tolerance but is less convenient and is rarely used routinely except for gestational diabetes and research?

• A. Fasting plasma glucose
• B. Oral glucose tolerance test
• C. HbA1c
• D. Urine glucose

Answer: (B)

The oral glucose tolerance test is used because it reveals how well the body handles a glucose challenge, not just how it sits at baseline. By giving a standardized 75 g glucose load and measuring the plasma glucose two hours later, it can detect abnormalities in glucose handling that fasting measures miss. This makes it more sensitive for diagnosing diabetes and impaired glucose tolerance, since someone may have a normal fasting glucose but an abnormal post-load glucose result. In contrast, fasting glucose looks only at baseline hepatic glucose production and fasting insulin action, and HbA1c reflects longer-term average blood sugar rather than peak post-load levels, so they can miss early or isolated postprandial problems. The downside is practical: it requires fasting, a lengthy procedure with multiple blood draws over about two hours, and more resources, which is why it isn’t used routinely except in pregnancy and research settings where precise assessment is needed.

The oral glucose tolerance test is used because it reveals how well the body handles a glucose challenge, not just how it sits at baseline. By giving a standardized 75 g glucose load and measuring the plasma glucose two hours later, it can detect abnormalities in glucose handling that fasting measures miss. This makes it more sensitive for diagnosing diabetes and impaired glucose tolerance, since someone may have a normal fasting glucose but an abnormal post-load glucose result. In contrast, fasting glucose looks only at baseline hepatic glucose production and fasting insulin action, and HbA1c reflects longer-term average blood sugar rather than peak post-load levels, so they can miss early or isolated postprandial problems. The downside is practical: it requires fasting, a lengthy procedure with multiple blood draws over about two hours, and more resources, which is why it isn’t used routinely except in pregnancy and research settings where precise assessment is needed.