Blood WorkFast for 8 to 12 hours before a fasting blood test: no food, and no drinks except plain water. Coffee, juice and soda are out, and so are gum, smoking and exercise. Only some tests need a fast: fasting glucose, fasting insulin, a cholesterol (lipid) panel and a metabolic panel, which covers most yearly panels. Take your usual medicines unless your clinician tells you otherwise.
How long should you fast before blood work?
Fast for 8 to 12 hours before your draw. Fasting means no food, and no drinks except plain water.
The easy way is to stop eating after dinner and get drawn first thing in the morning, so most of the fast happens while you sleep. Bring a snack to eat right after the draw.
You only need to fast if your order includes a test that requires it. If even one test on the order does, fast for the whole draw.
Which blood tests need fasting?
Four kinds of test need a fast. The rest don't.
| Test | Fast? | Good to know |
|---|---|---|
| Fasting glucose | Yes, 8 to 12 hours | Needs at least 8 hours without food. |
| Fasting insulin and HOMA-IR | Yes, 8 to 12 hours | Only mean something after a fast. Stop biotin (vitamin B7) supplements at least a day before. |
| Cholesterol (lipid) panel | Yes, 8 to 12 hours | We ask you to fast so the panel is easier to read. |
| Comprehensive metabolic panel | Yes, 8 to 12 hours | It includes glucose. |
| Hemoglobin A1c | No | It shows your average blood sugar over about three months. |
| Complete blood count (CBC) | No | |
| ApoB and Lp(a) | No | ApoB is reliable after a meal. |
| Kidney tests (eGFR, urine albumin) | No | |
| Thyroid tests (TSH, free T4) | No | |
| Ferritin and iron tests | No | Skip iron pills the morning of your draw. |
| Vitamin D, B12 and folate | No | |
| Testosterone, FSH and estradiol | No | Testosterone is best drawn before 10 a.m. and before eating. |
| PSA | No | Avoid sex or masturbation for 24 hours before the test. |
| Uric acid | No | A big meal, alcohol or hard exercise the day before can raise it. |
| Hepatitis B, hepatitis C and HIV tests | No |
Do Passion Health panels need fasting?
Seven of our nine panels include glucose or cholesterol, so they need a fast.
| Panel | Price | Fast? |
|---|---|---|
| Essential Blood Work | $59 | Yes, 8 to 12 hours |
| Full Blood Work | $149 | Yes, 8 to 12 hours |
| Blood Work + Visit | $199 | Yes, 8 to 12 hours |
| Diabetes & Kidney Panel | $69 | Yes, 8 to 12 hours |
| Thyroid Panel | $30 | No |
| Energy & Iron Panel | $119 | Yes, 8 to 12 hours |
| Men's Health Panel | $139 | Yes, 8 to 12 hours. Get drawn before 10 a.m. |
| Women's Midlife Panel | $145 | Yes, 8 to 12 hours |
| Infection Screening Panel | $70 | No |
Can you drink water when fasting for blood work?
Yes. Plain water is allowed for the whole fast, so drink it as you normally would.
Skip flavored water and flavored sparkling water, which may contain sugar or sweeteners.
Can you drink coffee before a fasting blood test?
No. During a fast you drink only plain water. Coffee, juice, soda and other drinks get into your bloodstream and can change your results, and that includes black coffee. The same goes for tea. Have your coffee after the draw.
What else should you avoid while fasting?
- Chewing gum.
- Smoking.
- Exercise.
- Alcohol. You may be asked to avoid it for longer than the fast.
Should you take your medicines while fasting?
Take your usual medicines with water unless your clinician tells you otherwise. Tell us about the vitamins and supplements you take, too.
- Iron pills: skip them the morning of your draw if your order includes iron tests.
- Biotin (vitamin B7): stop it at least a day before a fasting insulin test.
- Diabetes medicine: if you take insulin or another medicine that lowers blood sugar, ask your clinician how to fast before you start.
What if you ate or drank by mistake?
Tell the staff at the draw site before your blood is drawn, and tell us. Don't guess whether it matters.
You may need to come back another day so the results are accurate. Tests that don't need fasting can still be read.
Why do some blood tests need fasting?
When you eat or drink, sugar, fat and other nutrients move into your blood. That can change results such as glucose, insulin and triglycerides for several hours. Fasting gives your clinician a number that can be compared with standard ranges and with your own past results.
More fasting questions
How long should I fast before blood work?
8 to 12 hours, with nothing to eat or drink except plain water. You only need to fast if your order includes fasting glucose, fasting insulin, a cholesterol (lipid) panel or a metabolic panel.
Can I drink black coffee before a fasting blood test?
No. Only plain water is allowed during the fast. Coffee, including black coffee, can change your results, so have it after your draw.
Do I need to fast for a CBC?
No. A complete blood count doesn't need fasting. If it's drawn with a metabolic panel or cholesterol, as in Essential Blood Work, fast 8 to 12 hours for those.
Do I need to fast for an A1c test?
No. Hemoglobin A1c shows your average blood sugar over about three months and doesn't need fasting.
Do I need to fast for a thyroid test?
No. TSH and free T4 don't need fasting.
Do I need to fast for a PSA test?
No. Avoid sex or masturbation for 24 hours before a PSA test, because releasing semen can raise PSA.
Can I take my medicines while fasting?
Yes, with water, unless your clinician tells you otherwise.
What if I ate before my blood test?
Tell the staff at the draw site before your blood is drawn, and tell us. You may need to come back another day so the results are accurate.
Sources
- MedlinePlus, U.S. National Library of Medicine: Fasting for a Blood Test (updated August 28, 2025)
- MedlinePlus: Blood Glucose Test
- MedlinePlus: Insulin in Blood
- MedlinePlus: Cholesterol Levels
- MedlinePlus: Complete Blood Count (CBC)
- MedlinePlus: Testosterone Levels Test
- MedlinePlus: Prostate-Specific Antigen (PSA) Test