How To Do Venous Blood Sampling By Yiju Teresa Liu, MD, Harbor-UCLA Medical Center Reviewed / Revised Oct 2020 | Modified Sep 2022 View Patient Education Indications Contraindications Complications Equipment Additional Considerations Relevant Anatomy Positioning Step-by-Step Description of Procedure Warnings and Common Errors Aftercare Tips and Tricks Topic Resources Arterial and Venous Anatomy In venous blood sampling, a needle is inserted into a vein to collect a sample of blood for testing.