Understanding Your Fasting Blood Sugar Results
Feb 15, 2026 · Dr. L. Perera
A Fasting Blood Sugar (FBS) test measures the glucose in your blood after at least 8 hours without eating. It's one of the simplest and most useful tests to flag diabetes early — long before symptoms appear.
The reference ranges
| FBS reading | What it usually means |
|---|---|
| Below 100 mg/dL | Normal |
| 100–125 mg/dL | Pre-diabetes — early warning |
| 126 mg/dL or higher | Diabetes (if repeated) |
A single high reading isn't a diagnosis. Doctors typically confirm by repeating the test on a different day, often alongside an HbA1C to see your average sugar over the last 3 months.
How to prepare
- Fast for 8–12 hours before the test. Water is fine, no tea or coffee.
- Take your morning medication only if your doctor approved it.
- Schedule the test in the morning so you can eat right after.
When to retest
If you're healthy and your reading is normal, an annual check is usually enough. If you're in the pre-diabetes range, retest every 3–6 months while you make lifestyle changes — many people reverse pre-diabetes with diet and exercise alone.
Book at St. Luke's
We offer FBS as a walk-in test at our Ja-Ela lab or via home sample collection across Kandana, Welisara, Ragama, Wattala, Batagama and Thudella. Most reports back within 24 hours. Call 071 123 1954 to book.