We had this initial concern, but stopped allowing the alcohol swabbing and yet still had false positive results (affirmed by negative tests from another place with samples given just minutes after the first one). It was NOT the alcohol swab, in my opinion, validated by a toxicologist who reiterated that the test is NOT checking for alcohol, but for phosphatidyl ethanol, an alleged byproduct of the body’s processing of heavy alcohol consumption. The ONLY false positives I EVER received were from Forensic DNA & Testing in Dallas. To date, the three other test facilities have, rightly so since I don’t drink at all anymore, resulted in negative. My common denominator was FDNA.