longevity · 1 min read
Fasting for blood work: which tests actually require it
Fasting for blood work is still required for glucose, insulin and some metabolic panels, but increasingly not for lipids. Here is what to fast for, and for how long.
Written by Lifebar Desk · Checked against the sources listed below
Published 07 Aug 2026
Key takeaways
- Major guidelines now accept non-fasting lipid panels for routine screening.
- Fasting glucose, insulin and oral glucose tolerance testing still require 8 to 12 hours without food.
- Water, and usually black coffee, do not break a fast for laboratory purposes, but confirm with your lab.
Fasting before blood work is a habit that has partly outlived its evidence, and partly not.
Tests that still need a fast
| Test | Fast |
|---|---|
| Fasting plasma glucose | 8 hours |
| Fasting insulin / HOMA-IR | 8 to 12 hours |
| Oral glucose tolerance test | 8 to 12 hours |
| Triglycerides, when a precise value matters | 8 to 12 hours |
| Some iron studies | Morning, fasting preferred |
Tests that do not
Cholesterol panels for routine screening, HbA1c, thyroid function, full blood count, liver and kidney panels, vitamin D and B12 can all be drawn without fasting. A 2016 joint European consensus concluded non-fasting lipid measurement is appropriate for most clinical purposes, because post-meal changes are small and the practical advantages are large.
Why the change happened
People spend most of their lives in a fed state. Non-fasting lipids arguably reflect typical circulating levels better, and removing the fasting requirement improves screening uptake, fewer early appointments, fewer skipped tests.
Practical notes
- Water is encouraged; dehydration makes venipuncture harder and concentrates some values
- Alcohol raises triglycerides for a day or more, avoid it the night before
- Intense exercise can raise creatine kinase and some liver markers; keep the day before ordinary
- Take regular medications as prescribed unless your clinician says otherwise
Frequently asked
Can I drink coffee before a fasting blood test?
Black coffee is usually acceptable, though it can transiently affect glucose and lipids. If the test is glucose or insulin, water only is the safer choice.
What if I accidentally ate?
Tell the phlebotomist. Many tests can still be run and interpreted; some will simply be rescheduled.
Sources
Educational content, talk to your clinician before changing treatment.
