A patient in coma has negative immunoassay screens for multiple drugs and no ethanol detected. Can drug overdose be ruled out?

• A. No
• B. Yes
• C. Maybe
• D. Not enough information

Answer: (A)

Negative immunoassay screens do not rule out overdose. These tests are screening tools that detect only certain drug classes and rely on specific cutoffs, so a patient could have ingested a substance not included in the panel or present at a level below the assay’s detection limit. Timing also matters: if the drug hasn’t reached detectable levels yet, or has already been cleared, the result can be negative even in true overdose. In addition, many drugs, especially newer or less common ones, may not be detected by standard immunoassays or may appear only as metabolites not targeted by the test. Because of these limitations, a patient in coma with potential overdose requires clinical management and, if overdose is suspected, more comprehensive testing (like GC-MS or LC-MS/MS) and targeted toxicology studies, rather than relying on a negative screen alone.