In toxicology, which describes a presumptive test?

• A. A test to calibrate the instrument.
• B. A quick screening test indicating possible presence, followed by confirmatory testing.
• C. A test to measure blood alcohol content.
• D. A confirmatory test identifying exact substances.

Answer: (B)

Presumptive tests in toxicology are rapid, inexpensive screening methods used to signal that a substance might be present. They’re designed to be quick and simple, giving an initial indication rather than a definitive identification. Because results can be influenced by other substances, a positive presumptive test is followed by confirmatory testing using more specific, instrumental methods to identify and quantify the exact substance. This two-step approach is the reason the description fits best: a quick screening test indicating possible presence, followed by confirmatory testing.

Calibration or instrument setup is a quality-control step, not a test for substances. Measuring blood alcohol content is a precise quantitative test, not a screening presumptive test. A confirmatory test that identifies exact substances is the follow-up step after screening, not the initial presumptive test.