Most routine medical fasts run 8–12 hours, usually overnight. Your doctor will tell you to stop eating after dinner (around 8 PM) and come in for blood work the next morning. This gives enough time for glucose and lipid levels to stabilize for accurate readings. Some tests require longer fasts. A fasting glucose test needs at least 8 hours, while a full lipid panel often requires 9–12 hours for accurate triglyceride measurement. Certain metabolic panels or pre-surgical clearances can push to 10–14 hours, especially if you're scheduled for anesthesia. Water is almost always allowed during a medical fast—hydration doesn't interfere with most blood markers and makes it easier to draw blood. Black coffee is sometimes permitted for shorter fasts, but clarify with your clinic because some tests are sensitive to caffeine's effect on cortisol or glucose. Medications depend on the test; your doctor will specify which ones to take or skip. Pre-operative fasts are stricter. Most surgeons follow "NPO after midnight" protocols, meaning nothing by mouth (including water) for 6–8 hours before anesthesia. This prevents aspiration risk during intubation. Pediatric and diabetic patients often get modified instructions. From an SEO perspective, medical queries like this perform well when you answer the question upfront with the most common timeframe, then layer in the variations people actually search—fasting for blood work, surgery prep, glucose tests. Medical content ranks when it's specific and matches what patients type into Google at 6 AM before their lab appointment. At Ottawa SEO Inc., we see healthcare sites win featured snippets by structuring answers in clear ranges (8–12 hours) rather than vague "it depends" statements, then following with the practical details patients need to prepare. Always cite ranges from recognized medical guidelines (CMA, CDA, or provincial health authorities in Canada) if you're publishing this commercially, since health misinformation triggers quality rater scrutiny.