Screening Versus Confirmatory Tests

Presumptive Methods in medical and forensic science, also known as presumptive tests, are types of sample analysis which establish that either:
• ​The sample definitely does not contain a certain substance.
• The sample might contain a substance of interest to the analyst.

​Confirmatory tests are the tests required to confirm the analysis made initially by a presumptive test.   Confirmatory tests generally take more time and cost more than simpler presumptive tests; presumptive tests are often made on samples first to see if confirmatory tests are necessary on a sample.

Presumptive Tests:
• Narrow possibilities and help decide which test to do next.
• Can be used on larger areas at a crime scene.
• Can locate evidence not visible to naked eye.
• Are fairly sensitive.
• Have a higher risk of false positives.

​Confirmatory Tests:
• Can conclusively identify a substance if performed correctly.
• Have a smaller risk of false positives.
• Cost more.
• Require additional equipment.
• Take longer to perform.

​Types of Presumptive Tests:
• Color tests/spot tests.
• Microcrystalline tests.
• Ultraviolet spectroscopy.
• Infrared spectroscopy.
• Microscopic examinations.
• (TLC) Thin layer chromatography.

Types of Confirmatory Tests:
• Gas Chromatography /Mass Spectrometry (GCMS).
• Liquid Chromatography /Mass Spectrometry (LCMS).
• Infrared Spectroscopy.
• Nuclear Magnetic Resonance (NMR).

​For more information about standards and testing procedures for color test methods for determination of drugs of abuse, see the National Institute of Justice Law Enforcement and Corrections Standards and Testing Program: https://www.ojp.gov/pdffiles1/nij/183258.pdf

The site states that “The purpose of this standard is to establish minimum requirements for color test reagent/kits to detect drugs of abuse and methods of testing the reagents to determine compliance with those requirements.”