A patient in coma with negative results on standard immunoassay screens could still have an overdose due to substances not included in the screens. Which statement is true?

A patient in coma with negative results on standard immunoassay screens could still have an overdose due to substances not included in the screens. Which statement is true?

• A. Overdose can be ruled out.
• B. Overdose cannot be ruled out.
• C. Overdose can be ruled out if all screens are negative.
• D. Only overdoses of tested drugs are possible.

Answer: (B)

Negative results on standard immunoassay screens do not prove there is no overdose. Immunoassays test for a predefined set of drugs or drug classes, using antibodies that detect only those substances or closely related ones. A patient can overdose on substances that aren’t included in the standard panels, or on newer or synthetic drugs that the screens don’t detect. Timing also matters: drug levels might be too low at the time of testing or may have already fallen below detectable limits, leading to a false sense of safety. Because of these limitations, you cannot rule out overdose based solely on negative screens. If clinical suspicion remains, pursue broader toxicology testing with more comprehensive methods (like GC-MS or LC-MS) and treat based on the patient’s presentation and history.

Negative results on standard immunoassay screens do not prove there is no overdose. Immunoassays test for a predefined set of drugs or drug classes, using antibodies that detect only those substances or closely related ones. A patient can overdose on substances that aren’t included in the standard panels, or on newer or synthetic drugs that the screens don’t detect. Timing also matters: drug levels might be too low at the time of testing or may have already fallen below detectable limits, leading to a false sense of safety. Because of these limitations, you cannot rule out overdose based solely on negative screens. If clinical suspicion remains, pursue broader toxicology testing with more comprehensive methods (like GC-MS or LC-MS) and treat based on the patient’s presentation and history.