How to prepare for a fasting blood test: what you can and cannot do HealthcareOnTime Fasting for blood work typically involves avoiding food and drink (except water) for eight to twelve hours to ensure accurate results, particularly for tests like glucose, cholesterol, and triglycerides. It is important My fasting blood glucose on testing was higher than my post food glucose. Is it abnormal? Blood Plasma Quality Control by Plasma Glutathione Status