Fasting Blood Sugar (FBS) & PPBS
Also known as: Fasting Blood Glucose (FBG), Postprandial Blood Sugar (PPBS), Oral Glucose Tolerance Test (OGTT), Blood Sugar Test
Parameters Measured in the Report
A breakdown of individual biomarkers and biological reference intervals typically found in your report:
| Biomarker | Standard Range | Unit | What It Means |
|---|---|---|---|
Fasting Blood Sugar (FBS) (Fasting Glucose) | Normal: 70–99 Prediabetes: 100–125 Diabetes: ≥ 126 | mg/dL | Blood glucose level after an 8 to 10 hour overnight caloric fast. |
Postprandial Blood Sugar (PPBS) (2-Hour Post-Meal Glucose) | Normal: < 140 Prediabetes: 140–199 Diabetes: ≥ 200 | mg/dL | Blood glucose level exactly two hours after beginning a standard meal. |
Random Blood Sugar (RBS) (Random Glucose) | 70–140 (Diabetes suspect: ≥ 200 with symptoms) | mg/dL | Blood glucose measured at any time regardless of when the last meal was consumed. |
* Note: Reference ranges may vary slightly between testing instruments and reagent kits. Always refer to the reference interval printed on your specific pathology report.
Clinical Focus
Immediate concentration of glucose in the bloodstream after an overnight fast and post-meal.
Sample & Specimen
Venous blood (Sodium Fluoride grey-top tube)
Fasting Protocol
Strict overnight fasting of 8 to 10 hours required for FBS. Water is allowed.
Turnaround Time
2–4 hours (same day)
What Is This Test?
Why Did Your Doctor Order This Test?
Physicians routinely prescribe the FBS & PPBS in the following clinical scenarios:
How to Prepare Before Your Test
- Do not eat or drink any calorie-containing beverages for 8–10 hours before the morning FBS blood draw.
- Plain drinking water is permitted and encouraged to maintain vein hydration.
- For PPBS: Have your meal and note the exact time you take the first bite; the blood must be drawn precisely 120 minutes later.
Understanding Your Results
What higher or lower readings generally mean in clinical practice:
If Values Are Higher Than Normal
An FBS between 100–125 mg/dL indicates Impaired Fasting Glucose (prediabetes). An FBS of 126 mg/dL or higher on two separate tests confirms diabetes. In PPBS, levels above 200 mg/dL indicate significant insulin resistance or deficient pancreatic insulin secretion.
If Values Are Lower Than Normal
Blood glucose below 70 mg/dL is considered hypoglycemia. Symptoms include cold sweats, trembling, tachycardia, dizziness, and confusion. Severe hypoglycemia (<54 mg/dL) requires immediate fast-acting carbohydrate consumption and medical evaluation.
Frequently Asked Questions
Can I drink morning tea or black coffee before my fasting blood sugar test?
No. Even black coffee or unsweetened tea contains caffeine and compounds that stimulate liver glycogen breakdown and cortisol secretion, which can artificially skew your fasting glucose reading.
Related Laboratory Tests
Tests frequently prescribed together or used as follow-up investigations:
HbA1c (Glycated Hemoglobin)
Percentage of hemoglobin molecules chemically bound to glucose over the past 2 to 3 months.
Fasting Serum Insulin & HOMA-IR
Fasting blood insulin concentration and calculated mathematical Homeostatic Model Assessment of Insulin Resistance.
Lipid Profile (Cholesterol Panel)
Total Cholesterol, HDL (good cholesterol), LDL (bad cholesterol), VLDL, and Triglycerides.
Medical & Diagnostic Disclaimer
This guide is published for educational and patient informational purposes only. It is not a substitute for professional medical evaluation, diagnosis, or clinical advice.
A laboratory result that falls slightly outside standard statistical reference intervals does not automatically indicate disease; conversely, a normal result does not guarantee the absence of medical conditions. Only your attending physician can interpret lab findings in the context of your medical history, physical exam, and symptoms.