Blood alcohol and drug testing provides a highly accurate, real-time assessment of substances present in the bloodstream at the time of collection. It is often used in medical, forensic, legal, and impaired-driving investigations because it reflects current or very recent use rather than historical exposure. Blood drug testing identifies parent compounds and active metabolites, offering precise concentration levels that support clinical and legal interpretation. The phosphatidylethanol (PEth) test is a specialized blood biomarker used to evaluate alcohol consumption over the previous 2–4 weeks, making it particularly valuable for monitoring chronic or repeated alcohol use. Unlike standard blood alcohol testing, PEth is only formed in the presence of ethanol, eliminating false positives from incidental exposure. All blood collections follow strict phlebotomy, handling, and laboratory confirmation protocols to ensure accuracy, reliability, and defensibility of results.