Blood sugar tests measure the amount of glucose (sugar) in your blood. Glucose is your body’s main source of energy, but too much or too little can indicate health problems, most commonly diabetes.
Doctors often order three types of blood sugar tests to get a full picture:
1. Fasting Blood Sugar (FBS)
- Purpose: Measures blood sugar after not eating or drinking (except water) for at least 8 hours.
- Normal Range: 70–99 mg/dL
- High: May indicate diabetes, prediabetes, stress, or certain medications.
- Low: May suggest hypoglycemia, excessive insulin, or prolonged fasting.
2. Random Blood Sugar (RBS)
- Purpose: Taken at any time of the day, regardless of when you last ate.
- Normal Range: Usually less than 140 mg/dL.
- High: A reading above 200 mg/dL along with symptoms may indicate diabetes.
3. Postprandial Blood Sugar (PPBS)
- Purpose: Measures blood sugar exactly 2 hours after starting a meal.
- Normal Range: Less than 140 mg/dL.
- High: Can indicate impaired glucose tolerance or diabetes.
Why Doctors Recommend This Test
- Diagnose diabetes or prediabetes.
- Monitor treatment in diabetic patients.
- Detect hypoglycemia (low blood sugar).
- Investigate symptoms like excessive thirst, frequent urination, unexplained weight changes, or fatigue.
Test Preparation
- FBS: Fast for 8–10 hours (only water allowed).
- PPBS: Eat a normal meal, then test exactly 2 hours later.
- RBS: No special preparation needed.
- Avoid heavy exercise before the test and tell your doctor about any medicines you take.
What Patients Should Know
- It’s a quick, safe blood test from a vein or finger prick.
- Results are usually available within a few hours.
- Abnormal results may require repeat testing or additional tests like HbA1c.
- Consistently high blood sugar can damage the heart, kidneys, eyes, and nerves.
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