What are Blood Sugar Tests?
Blood glucose tests are used for the following purposes:
- Diagnosis of diabetes, especially in a patient with clinical features of diabetes
- Screening for diabetes, which is normally done in individuals at 45 years of age or above. It should be started earlier if a person is overweight or obese and has one additional risk factor for developing diabetes
- Monitoring the control of diabetes once it is diagnosed
- Adjusting the dosage of medication. Hospitalized diabetic patients may require testing even 2 to 3 times a day to maintain the blood sugar under control.
How is a Blood Sugar Test Done?There are several ways to test for diabetes based on the blood glucose. All the tests require a sample of blood. Some tests are carried out in the fasting state, some after a specific time following eating, and some at random.
Some of these methods are as follows:
Hemoglobin A1C level: The hemoglobin A1C or glycated hemoglobin is a blood test that reflects the percentage of hemoglobin that is attached to glucose. The salient features of the test are:
- The test is useful to find out the blood glucose status for the last three months, since the lifespan of the red blood cells is three months.
- The test can be done at any time and does not require fasting
- The results are not affected by acute conditions like stress and illnesses
- It can be used to predict some of the complications of diabetes
- Depending on the result, the condition can be classified as:
- Normal: less than 5.7%
- Prediabetes: 5.7%-6.4%
- Diabetes: More than 6.4%
- The disadvantage of this test is that it is not as sensitive as other blood glucose tests and is expensive
Fasting Plasma Glucose Level: The fasting plasma glucose levels indicate the blood glucose levels in the fasting state:
- The blood sample is obtained in the morning after overnight fasting for 8 hours
- The test is available in most laboratories and is relatively cheap
- Depending on the result, the condition can be diagnosed as:
- Normal - 80-100 mg/dL
- Impaired fasting glucose or prediabetes - 100-125 mg/dL
- Diabetes - ≥ 126 mg/dL
Oral glucose tolerance test: The oral glucose tolerance test is a sensitive method of testing for diabetes. Its salient features are:
- The blood glucose levels are measured after overnight fasting and 2 hours after a standard glucose drink (postprandial)
- The test is often used to detect gestational diabetes, that is diabetes that first appears in pregnancy
- If the postprandial result is abnormal, the condition can be diagnosed as:
- Prediabetes or impaired glucose tolerance (IGT) - 140-199 mg/dL at 2 hours
- Diabetes - ≥ 200 mg/dL at 2 hours
- The test is sensitive. However, it is cumbersome to perform.
- The test is not very sensitive and is usually not preferred
- It is particularly useful to confirm diabetes in a patient already suffering from the symptoms, that is, polyuria, polydipsia, polyphagia, and unexplained weight loss
- A reading of 200 mg/dL with this test confirms the presence of diabetes