Which tests require fasting?
| Test | Fasting Required? | Fasting Duration |
|---|---|---|
| Fasting Blood Sugar (FBS) | Yes | 8–12 hours |
| HbA1c | No | Any time |
| Lipid Profile (Cholesterol) | Yes (ideal) | 9–12 hours |
| KFT (Creatinine, Urea) | No | Any time |
| LFT (Liver Function) | Preferred | 8 hours |
| CBC (Blood Count) | No | Any time |
| Thyroid (TSH) | No | Any time (morning preferred) |
| Vitamin D, B12 | No | Any time |
| Ferritin / Iron Studies | Preferred | 8 hours (morning) |
| Uric Acid | Preferred | 4–8 hours |
| CRP / ESR | No | Any time |
| PSA (Prostate) | No | Any time (avoid ejaculation 48hr before) |
| Urine Routine | No | First morning sample preferred |
Can I drink water while fasting?
YES — plain water is allowed and recommended
Drinking plain water (no sugar, no flavouring) during a fasting period does NOT affect blood sugar, lipid or most other test results. In fact, drinking water before the test helps: it keeps you hydrated, makes veins easier to find, and reduces dizziness after blood is drawn. Drink 2–3 glasses of plain water before your test.
What you CANNOT have during fasting
- Tea or coffee — even without sugar. Caffeine and milk affect test results
- Fruit juice — high sugar content spikes blood glucose
- Any food — biscuits, fruits, anything solid
- Chewing gum — stimulates insulin release
- Alcohol — affects liver enzymes and triglycerides for 24–48 hours
What about medications?
Take most regular medications with a sip of water
Unless your doctor specifically says to skip your medications before the test, continue taking them with a small sip of water. This especially applies to blood pressure medication, thyroid medication (levothyroxine) and heart medications — missing a dose can be dangerous. However: avoid metformin if you're having a contrast scan same day. Always ask your doctor or lab for specific guidance on your medications.
Best time to get a fasting blood test
What happens if I accidentally ate?
Tell the lab technician and your doctor immediately. For fasting blood sugar and lipid profile, eating beforehand will give falsely elevated results. Most labs will reschedule rather than draw an inaccurate result. For tests that don't require fasting, eating is not a problem at all.
Special situations
- Diabetics: Ask your doctor specifically whether to take insulin or diabetes tablets before a fasting test
- Children under 5: Prolonged fasting can cause hypoglycaemia — ask your paediatrician for specific guidance
- Pregnant women: Keep the fasting period shorter (6–8 hours maximum) and eat immediately after
- Thyroid medication (levothyroxine): TSH is ideally measured before taking the morning dose