Fasting Blood Glucose (FBG) measures blood sugar levels after an 8-12 hour fast and is one of the primary tests used to diagnose diabetes and prediabetes.
| Fasting Blood Glucose (mg/dL) | Interpretation |
|---|---|
| < 100 | Normal |
| 100 – 125 | Prediabetes (Impaired fasting glucose) |
| ≥ 126 (on two occasions) | Diabetes Mellitus |
🔹 FBG ≥ 126 mg/dL on two separate tests confirms diabetes.
✅ Screening for diabetes and prediabetes
✅ Monitoring blood sugar control in diabetics
✅ Evaluating metabolic health and insulin function
✅ Checking for hypoglycemia (low blood sugar) in certain conditions
| Cause | Explanation |
|---|---|
| Diabetes Mellitus (Type 1 & 2) | Insulin deficiency or resistance |
| Prediabetes | Early stage of insulin resistance |
| Cushing’s Syndrome | Excess cortisol raises glucose |
| Chronic stress & lack of sleep | Increased stress hormones affect glucose levels |
| Steroid medications (e.g., prednisone) | Increase blood sugar levels |
| Cause | Explanation |
|---|---|
| Insulin overdose | Too much insulin lowers blood sugar |
| Prolonged fasting or malnutrition | Depletes glucose stores |
| Liver disease (e.g., cirrhosis) | Impaired glucose production |
| Hormonal disorders (e.g., Addison’s disease, hypothyroidism) | Affects glucose regulation |
Patient fasts for 8-12 hours (only water is allowed).
Blood sample is taken in the morning.
Result is analyzed to assess glucose levels.
🔹 FBG should be tested in the morning before eating or drinking anything except water.
| Test | Purpose | Diabetes Range |
|---|---|---|
| HbA1c (Glycated Hemoglobin) | Averages blood sugar over 3 months | ≥ 6.5% |
| Postprandial Blood Glucose (PPBG, 2 hr after meal) | Measures glucose after a meal | ≥ 200 mg/dL |
| Oral Glucose Tolerance Test (OGTT – 2 hr) | Measures glucose after a sugar drink | ≥ 200 mg/dL |
🔹 HbA1c is the best test for long-term blood sugar control.
✅ FBG ≥ 126 mg/dL (on two occasions) confirms diabetes.
✅ Used for both diabetes screening and monitoring.
✅ Hyperglycemia is linked to diabetes, stress, and steroid use.
✅ Hypoglycemia can result from insulin overdose, fasting, or liver disease.
✅ Best combined with HbA1c and postprandial glucose for a complete picture.