A simple guide to making sure your labs reflect your true health
Preparing properly for lab work is one of the easiest ways to ensure your results are accurate, meaningful, and truly reflective of your health. Whether your labs are routine or part of an advanced functional medicine panel, the steps you take in the 24–48 hours beforehand can significantly influence your numbers.
Below is a clear, step-by-step guide covering fasting, supplements, what to avoid, menstrual cycle timing, and what to expect when getting labs..
Fasted vs. Non-Fasted Labs: What’s the Difference?
Not all labs require fasting. Your clinician will specify which tests need it, but here’s a quick breakdown:
Labs That Typically Do Require Fasting (8–12 hours)
- Glucose & insulin
- Lipid panel (cholesterol, triglycerides)
- Comprehensive metabolic panel (depending on your provider’s preference)
- Certain hormone tests (leptin, adiponectin, cortisol, TSH)
Fasting means:
- No food for 8–12 hours
- No coffee (yes—even black coffee can alter glucose, cortisol, lipids, and hydration status)
- Only water is allowed
- No electrolytes in your water
Labs That Usually Do Not Require Fasting
- CBC
- Iron labs (though some providers prefer fasting)
- Most reproductive hormones
- Vitamin D
- Specialty stool tests
- Salivary and urine hormone tests
If you’re unsure, always follow your provider’s instructions. When in doubt, ask us—we’re happy to clarify.
Which Supplements and Medications to Stop Before Testing
Certain supplements and medications can interfere with lab accuracy. Your provider will give you personalized instructions, but general guidelines include:
Stop 24–72 hours before labs (unless instructed otherwise):
- Biotin (vitamin B7) → can falsely alter thyroid, hormone, and cardiac markers
- High-dose vitamins (A, D, E, K, C) → may skew nutrient markers
- Herbal supplements (ashwagandha, rhodiola, berberine, ginseng) → can affect cortisol, glucose, and liver enzymes
- Iron supplements → may elevate iron/ferritin temporarily
- NSAIDs (ibuprofen/naproxen) → may alter kidney function or inflammation markers
DO NOT stop prescription medications unless your provider instructs you.
Always ask if you’re unsure.
Hydrate, Hydrate, Hydrate!
Hydration is one of the most overlooked parts of lab prep.
Why hydration matters:
- Improves vein fullness (easier blood draw)
- Prevents falsely elevated kidney markers
- Helps stabilize electrolyte levels
- Reduces dizziness after labs
Aim for:
- 8–16 oz of water before bed
- 16 – 32 oz of water when you wake up
Why No Coffee Before Labs?
Even black coffee can impact your results by:
- Raising cortisol
- Affecting fasting glucose
- Altering lipid levels
- Causing dehydration
- Increasing gastric activity (affecting GI markers)
For truly accurate labs, save the coffee for after your appointment.
Avoid Vigorous Exercise the Morning of Your Labs
High-intensity exercise can temporarily change:
- Cortisol
- Inflammatory markers (CRP)
- Blood sugar
- Kidney markers
- Liver enzymes
- Electrolytes
Light walking is fine—but skip intense cardio, weight training, or sweating heavily before your draw.
Menstrual Cycle Timing Matters
Hormone results vary depending on your cycle phase. For the most accurate reproductive hormone testing:
Best Day for Sex Hormones (Estradiol, Progesterone, LH, FSH):
- Cycle Day 19–21 → mid-luteal phase is when we expect hormones to peak. This is for someone who has a regular, 28-day cycle.
- The most accurate way to check mid-luteal phase hormones is 5-7 days after ovulation. You can confirm when you ovulate with LH strips.
If your cycle is irregular:
We’ll guide you individually—just let us know your cycle patterns.
For DUTCH testing, stool tests, and many functional panels:
Timing may be more specific—your kit will include instructions, but you can always reach out if you need clarification.
The Day of Your Lab Appointment: A Simple Checklist
- □ Fast 8–12 hours if required
- □ Only water (no coffee, tea, gum, mints)
- □ Hydrate well
- □ Skip morning supplements
- □ Skip morning exercise
- □ Bring your photo ID
- □ Bring printed lab order or lab kit only if needed
- □ Plan a protein-rich meal afterward (you’ll feel better!) and enjoy your coffee!
Final Thoughts
Preparation matters. By following these steps, you’ll ensure your results are clear, accurate, and truly reflective of your health—so your provider can create the most effective plan for you.
If you’re ever unsure about fasting, timing, supplements, or where to go for testing, don’t hesitate to reach out. We’re here to make the process simple and stress-free.
