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Fasting, hydration, medicines, and preparing for a Blood Test

Correct preparation protects the quality and usefulness of your laboratory results.

Preparation depends on the exact test. Some panels require fasting for a stated number of hours. Others do not. Some require morning collection, medication timing, or information about supplements and recent exercise.

Follow the specific test instructions

The preparation shown for your selected panel takes priority over general advice. If instructions are unclear, ask before the collection rather than guessing.

Fasting

  • Start fasting at the stated time

  • Do not eat food, chew gum, or consume caloric drinks during the fasting period unless instructed otherwise

  • Plain water is often allowed and can help with collection, but confirm the instructions for your test

  • Do not extend a fast unnecessarily

  • Tell the collector if the fasting period was not completed

Medicines and supplements

Do not stop a prescribed medicine unless the treating clinician has told you to do so. Share the medicine, supplement, and dose information requested because some products can affect results.

Hydration

Normal hydration can make venous collection easier and can reduce the effects of dehydration on some values. Avoid excessive fluid intake unless specifically directed.

Exercise, alcohol, and sleep

Hard exercise, alcohol, poor sleep, acute illness, and stress can affect certain results. Follow panel-specific advice and tell the clinician about relevant circumstances when results are interpreted.

If preparation was not followed

Tell the collector before the sample is taken. The safest option may be to proceed with a note, change the test, or reschedule. Hiding the issue can make the result misleading.

Review preparation on the specific live test page.

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