Hello @brundle -- I would like to add my welcome to Connect along with @lisalucier. I did a search and found an article on the National Institutes of Health site that has an extensive section on PEth testing.

Biomolecules and Biomarkers Used in Diagnosis of Alcohol Drinking and in Monitoring Therapeutic Interventions
-- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4598755/

I also found a lot of research information on Google Scholar (https://scholar.google.com/) using the search phrase "peth alcohol test false positive". Here are the search results links:
-- https://scholar.google.com/scholar?as_ylo=2018&q=peth+alcohol+test+false+positive&hl=en&as_sdt=1,24&as_vis=1

Hoping you find some answers...

John