Patient Preparation Guide for Blood Chemistry and CBC Testing Before 6:00 AM
For your early morning blood work (complete blood chemistry panel with CBC), you must fast for 8 hours before your 6:00 AM appointment, which means no food or drink except plain water after 10:00 PM the night before. 1
The Night Before Your Test
Stop Eating and Drinking By 10:00 PM
- No food after 10:00 PM - Your last meal should be at least 8 hours before your blood draw 1
- Avoid fried or fatty foods for dinner, as these require even longer fasting periods (8+ hours) 1
- No alcohol during your fasting period, as it interferes with test results 1
- No caffeinated beverages (coffee, tea, energy drinks) after 10:00 PM 1
What You CAN Have
- Plain water is encouraged throughout the fasting period and morning before your test - drink freely without restriction 1
- Water does not interfere with test results and actually helps with blood draw 1
Medication Instructions
- Continue your regular medications unless specifically instructed otherwise by your physician 2
- Take medications with water if needed 1
The Morning of Your Test
Before Leaving Home
- No breakfast - arrive fasting 1
- No coffee, tea, or juice - only plain water 1
- Drink water to stay hydrated 1
Exercise Restrictions
- Avoid vigorous exercise for at least 2 hours before your blood test 3
- Strenuous activity can temporarily elevate blood glucose and other parameters that persist for 1-2 hours 3
- Light walking to the laboratory is acceptable 3
What to Wear
- Wear comfortable clothing with sleeves that can be easily rolled up 2
Important Timing Considerations
Why 6:00 AM Matters
- Blood should be drawn before 10:00 AM to account for natural daily fluctuations in biomarker levels 1
- Early morning testing provides the most accurate and standardized results 1
Fasting Duration Limits
- Do not fast longer than 12 hours - prolonged fasting can cause hypoglycemia and alter blood values 1
- If you have diabetes, fasting longer than 8 hours may be particularly problematic 1
Special Populations Requiring Modified Instructions
If You Have Diabetes
- Consult your physician about specific fasting instructions 1
- You may need individualized guidance regarding insulin or medication timing 1
If You Have Gastroesophageal Reflux or Delayed Gastric Emptying
- Contact your ordering physician for modified fasting instructions 1
What Happens If You Don't Follow These Instructions
Food consumption significantly impacts CBC and chemistry results - studies show that red blood cell count, hemoglobin, hematocrit, platelet count, and white blood cell differential all change after eating 4. Specifically:
- Red blood cells, hemoglobin, and hematocrit decrease 2 hours after meals 4
- Lymphocyte counts decrease while neutrophil counts increase after food intake 4
- Glucose and lipid measurements become inaccurate 1
If you eat or drink anything other than water, inform the laboratory staff immediately - your test may need to be rescheduled to ensure accurate results 4, 5.
Day of Test Checklist
✓ Fasted since 10:00 PM (8 hours minimum, 12 hours maximum) 1
✓ Drank only plain water 1
✓ No vigorous exercise for 2+ hours 3
✓ Took regular medications with water 2
✓ Wearing comfortable clothing 2
✓ Arrive well-hydrated 1