Phosphatidylethanol (PEth) is a mid-to-long-term alcohol biomarker created in red blood cells, where it exists as part of the cell membrane. We offer PEth testing in dried blood spots and whole blood (venipuncture). PEth may be detected in blood for up to approximately 2-4 weeks. However, there may be isolated circumstances where PEth may be detected at 6 weeks or more.