Drug and Substance Blood Test Results Explained

Substance Testing: Understanding Your Screening Results

Substance testing blood work can come as part of a pre-employment screening, a legal requirement, a medical workup, or personal health monitoring. Whatever brought you here, you probably have questions about what the results mean, what counts as "positive," and whether there is any chance of a false result. Let me break it down.

Blood-based substance tests detect drugs or their metabolites circulating in your system. Unlike urine tests that show use over days or weeks, blood tests generally reflect more recent use. Each substance has a different detection window in blood.

Tests Included in Substance Panels

• 5-Panel Drug Screen - the most common employment test, covers amphetamines, cannabis (THC), cocaine, opiates, and PCP
• 10-Panel Drug Screen - adds barbiturates, benzodiazepines, methadone, propoxyphene, and methaqualone
• Expanded Opioid Panel - tests for specific opioids like fentanyl, oxycodone, hydrocodone, tramadol, and buprenorphine
• Alcohol (Ethanol) Level - measures current blood alcohol concentration
• CDT (Carbohydrate-Deficient Transferrin) - a biomarker that indicates heavy alcohol use over the past 2-3 weeks
• PEth (Phosphatidylethanol) - a newer alcohol biomarker that reflects drinking patterns over the past 3-4 weeks
• GGT (Gamma-Glutamyl Transferase) - a liver enzyme that is sensitive to alcohol use
• Therapeutic Drug Monitoring (TDM) - measures medication levels to ensure they are in the effective and safe range

False Positives Are Real

Immunoassay screening tests (the first-pass tests used in most panels) are designed to cast a wide net. That means they sometimes react to substances that are chemically similar to the target drug. Poppy seeds can trigger a positive opiate result. Certain cold medications containing pseudoephedrine can flag for amphetamines. Some NSAID pain relievers have been reported to cause false positives for THC.

That is why any positive screening result should be confirmed with a more specific test, usually GC-MS (gas chromatography-mass spectrometry) or LC-MS/MS. The confirmatory test identifies the exact substance and eliminates false positives.

Alcohol Biomarkers

A standard blood alcohol level only tells you if someone is currently intoxicated. CDT and PEth go further by revealing patterns of heavy drinking over weeks. These are increasingly used in legal, medical, and occupational settings where demonstrating sustained sobriety matters.

When Substance Testing Happens

Pre-employment screening. Random workplace testing. Probation or legal requirements. Medical monitoring during pain management or addiction treatment. Post-accident testing. Or personal curiosity about how your body is processing a medication.

Upload your substance test results and get a clear, non-judgmental explanation of every marker.

Upload your substance test results and I will explain what each one means.