A blood sugar test measures the amount of glucose in your blood at the time of sampling. The fasting blood sugar (FBS) test is done after 8–10 hours without food; normal is 70–99 mg/dL. The post-prandial (PP) test is done 2 hours after a meal; normal is below 140 mg/dL. Both help screen for diabetes.
What does the blood sugar test measure?
Glucose is your body’s main fuel. After you eat, blood sugar rises and the hormone insulin moves it into your cells. In diabetes, the body either makes too little insulin or stops responding to it well, so sugar stays high and slowly damages the heart, kidneys, eyes and nerves.
Different sugar tests are taken at different times:
- Fasting blood sugar (FBS): After at least 8 hours without food. Shows how well your body controls sugar overnight.
- Post-prandial blood sugar (PPBS): Exactly 2 hours after starting a normal meal. Shows how well your body handles a food load.
- Oral glucose tolerance test (OGTT): A fasting sample, then a measured 75 g glucose drink, then a sample 2 hours later. Used for formal diagnosis and in pregnancy.
- Random blood sugar (RBS): Taken at any time, regardless of meals.
Fasting and PP sugars are a snapshot of a single moment. For an average over the past few months, doctors add an HbA1c test.
Blood sugar normal range (adults, not pregnant)
Prediabetes 100–125
Diabetes 126 or above
Prediabetes 140–199
Diabetes 200 or above
Where does your result fall?
Enter your Fasting blood sugar value from your report.
A general guide, not a diagnosis. The reference range on your own report takes priority, and a doctor should interpret any result outside it.
Diagnostic cut-offs follow American Diabetes Association criteria and need confirmation with a repeat test. Pregnancy uses different, lower thresholds. Ranges vary between labs and methods. Always compare your result with the reference range printed on your own report.
What abnormal results can mean
- Fasting 100–125 mg/dL or 2-hour 140–199 mg/dL: Prediabetes. Lifestyle changes at this stage can often delay or prevent diabetes.
- Fasting 126 mg/dL or above, or 2-hour 200 mg/dL or above: Suggests diabetes, confirmed with a repeat test or HbA1c.
- Below 70 mg/dL: Low blood sugar; most common in people taking diabetes medicines.
Illness, stress, steroids and poor sleep can raise sugar temporarily. Discuss results with your doctor.
Who should get this test?
- Adults over 30, yearly, as diabetes appears earlier in South Asians.
- Anyone with risk factors: excess weight around the waist, family history, high blood pressure, PCOS, or past gestational diabetes.
- People with symptoms: frequent urination, thirst, unexplained weight loss, blurred vision or slow-healing wounds.
- People with diabetes, to monitor treatment.
- Preparation for FBS: Fast for 8–10 hours (water is allowed). Do not take diabetes medicines before the test unless your doctor says so.
- Preparation for PPBS: Eat your usual meal and give the sample exactly 2 hours after the first bite.
This page is for general information and is not a substitute for medical advice. Always interpret your results with a qualified doctor.