A 2-hour postprandial blood glucose test 20 minutes late can have some effect. A 2-hour postprandial blood glucose test that is 20 minutes late may have some impact. This is because insulin secretion in the body changes over time after eating, so blood glucose values fluctuate. Two-hour postprandial blood glucose reflects insulin secretion and the body’s sensitivity to insulin, and is an indicator often used to assess the condition and adjust medication. However, if the test is taken 20 minutes later, the time is longer and the true blood glucose level may not be detected. Patients are generally advised to test their postprandial blood glucose on time. Abnormal blood glucose is recommended to seek prompt medical attention.