Presumptive and confirmatory tests

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Presumptive tests, in medical and forensic science, analyze a sample and establish one of the following:

  1. The sample is definitely not a certain substance.
  2. The sample probably is the substance.

For example, the Kastle–Meyer test will show either that a sample is not blood or that the sample is probably blood but may be a less common substance. Further chemical tests are needed to prove that the substance is blood.

Confirmatory tests are the tests required to confirm the analysis. Confirmatory tests cost more than simpler presumptive tests so presumptive tests are often done to see if confirmatory tests are necessary.

Similarly, in medicine, a presumptive diagnosis identifies the likely condition of a patient, and a confirmatory diagnosis is needed to confirm the condition.

Examples

FDA recommendations

The US Food and Drug Administration issued a Premarket Submission and Labeling Recommendations for Drugs of Abuse Screening Tests. Its availability was announced in the Federal Register, Vol. 68, No. 231 on December 2, 2003 and is listed under "Notices." Presumptive testing has found widespread use by employers and public entities. Most people who take a drug test take a presumptive test, cheaper and faster than other methods of testing. However, it is less accurate and can render false results. The FDA recommends for confirmatory testing to be conducted and the placing of a warning label on the presumptive drug test: "This assay provides only a preliminary result. Clinical consideration and professional judgment should be applied to any drug of abuse test result, in evaluating a preliminary positive result. To obtain a confirmed analytical result, a more specific alternate chemical method is needed. Gas chromatography/mass spectrometry (GC/MS) is the recommended confirmatory method."

Related Research Articles

Marquis reagent is used as a simple spot-test to presumptively identify alkaloids as well as other compounds. It is composed of a mixture of formaldehyde and concentrated sulfuric acid, which is dripped onto the substance being tested. The United States Department of Justice method for producing the reagent is the addition of 100 mL of concentrated (95–98%) sulfuric acid to 5 mL of 40% formaldehyde. Different compounds produce different color reactions. Methanol may be added to slow down the reaction process to allow better observation of the colour change.

<span class="mw-page-title-main">Urinalysis</span> Array of tests performed on urine

Urinalysis, a portmanteau of the words urine and analysis, is a panel of medical tests that includes physical (macroscopic) examination of the urine, chemical evaluation using urine test strips, and microscopic examination. Macroscopic examination targets parameters such as color, clarity, odor, and specific gravity; urine test strips measure chemical properties such as pH, glucose concentration, and protein levels; and microscopy is performed to identify elements such as cells, urinary casts, crystals, and organisms.

A drug test is a technical analysis of a biological specimen, for example urine, hair, blood, breath, sweat, or oral fluid/saliva—to determine the presence or absence of specified parent drugs or their metabolites. Major applications of drug testing include detection of the presence of performance enhancing steroids in sport, employers and parole/probation officers screening for drugs prohibited by law and police officers testing for the presence and concentration of alcohol (ethanol) in the blood commonly referred to as BAC. BAC tests are typically administered via a breathalyzer while urinalysis is used for the vast majority of drug testing in sports and the workplace. Numerous other methods with varying degrees of accuracy, sensitivity, and detection periods exist.

<span class="mw-page-title-main">Forensic toxicology</span> Use of toxicology for investigations

Forensic toxicology is the use of toxicology and disciplines such as analytical chemistry, pharmacology and clinical chemistry to aid medical or legal investigation of death, poisoning, and drug use. The primary concern for forensic toxicology is not the legal outcome of the toxicological investigation or the technology utilized, but rather the obtention and interpretation of results. A toxicological analysis can be done to various kinds of samples. A forensic toxicologist must consider the context of an investigation, in particular any physical symptoms recorded, and any evidence collected at a crime scene that may narrow the search, such as pill bottles, powders, trace residue, and any available chemicals. Provided with this information and samples with which to work, the forensic toxicologist must determine which toxic substances are present, in what concentrations, and the probable effect of those chemicals on the person.

In chemistry, a chemical test is a qualitative or quantitative procedure designed to identify, quantify, or characterise a chemical compound or chemical group.

<span class="mw-page-title-main">Kastle–Meyer test</span> Blood test utilizing phenolphthalein

The Kastle–Meyer test is a presumptive blood test, first described in 1903, in which the chemical indicator phenolphthalein is used to detect the possible presence of hemoglobin. It relies on the peroxidase-like activity of hemoglobin in blood to catalyze the oxidation of phenolphthalin into phenolphthalein, which is visible as a bright pink color. The Kastle–Meyer test is a form of catalytic blood test, one of the two main classes of forensic tests commonly employed by crime labs in the chemical identification of blood. The other class of tests used for this purpose are microcrystal tests, such as the Teichmann crystal test and the Takayama crystal test.

<span class="mw-page-title-main">Reagent testing</span> Tests for authentication of psychoactive drugs, and detection of adulterants

Reagent testing is one of the processes used to identify substances contained within a pill, usually illicit substances. With the increased prevalence of drugs being available in their pure forms, the terms "drug checking" or "pill testing" may also be used, although these terms usually refer to testing with a wider variety of techniques covered by drug checking.

Ehrlich's reagent or Ehrlich reagent is a reagent containing p-dimethylaminobenzaldehyde (DMAB) and thus can act as an indicator to presumptively identify indoles and urobilinogen. Several Ehrlich tests use the reagent in a medical test; some are drug tests and others contribute to diagnosis of various diseases or adverse drug reactions. It is named after Nobel Prize winner Paul Ehrlich who used it to distinguish typhoid from simple diarrhoea.

Forensic serology is the detection, identification, classification, and study of various bodily fluids such as blood, semen, saliva, and urine, and their relationship to a crime scene. A forensic serologist may also be involved in DNA analysis and bloodstain pattern analysis. Serology testing begins with presumptive tests which gives the analyst an indication that a specific bodily fluid may be present, but cannot completely confirm its presence. Following the presumptive tests, confirmatory tests are done on the same sample to confirm what the unknown substance actually is.

The Liebermann reagent named after Hungarian chemist Leo Liebermann (1852-1926) is used as a simple spot-test to presumptively identify alkaloids as well as other compounds. It is composed of a mixture of potassium nitrite and concentrated sulfuric acid. 1 g of potassium nitrite is used for every 10 mL of sulfuric acid. Potassium nitrite may also be substituted by sodium nitrite. It is used to test for cocaine, morphine, PMA and PMMA.

The Mecke reagent is used as a simple spot-test to presumptively identify alkaloids as well as other compounds. It is composed of a mixture of selenous acid and concentrated sulfuric acid, which is dripped onto the substance being tested.

The Mandelin reagent is used as a simple spot-test to presumptively identify alkaloids as well as other compounds. It is composed of a mixture of ammonium metavanadate and concentrated sulfuric acid. Its primary use is for the detection of ketamine and PMA Unlike the most common reagent test chemicals, it has a deep red colour that changes to yellow if there is no alkaloid, which occurs within about 48 hours of mixing.

Simon's reagent is used as a simple spot-test to presumptively identify alkaloids as well as other compounds. It reacts with secondary amines like MDMA and methamphetamine to give a blue solution.

The Froehde reagent is used as a simple spot-test to presumptively identify alkaloids, especially opioids, as well as other compounds. It is composed of a mixture of molybdic acid or a molybdate salt dissolved in hot, concentrated sulfuric acid, which is then dripped onto the substance being tested.

The Dille–Koppanyi reagent is used as a simple spot-test to presumptively identify barbiturates. It is composed of a mixture of two solutions. Part A is 0.1 g of cobalt(II) acetate dihydrate dissolved in 100 ml of methanol mixed with 0.2 ml of glacial acetic acid. Part B made up of is 5% isopropylamine (v/v) in methanol. Two drops of A are dropped onto the substance followed by one drop of B and any change in colour is observed.

The Zwikker reagent is used as a simple spot-test to presumptively identify barbiturates. It is composed of a mixture of two solutions. Part A is 0.5 g of copper (II) sulfate in 100 ml of distilled water. Part B consists of 5% pyridine (v/v) in chloroform. One drop of each is added to the substance to be tested and any change in colour is observed.

<span class="mw-page-title-main">Cannabis drug testing</span> Drug test methodologies for the use of cannabis

Cannabis drug testing describes various drug test methodologies for the use of cannabis in medicine, sport, and law. Cannabis use is highly detectable and can be detected by urinalysis, hair analysis, as well as saliva tests for days or weeks.

The Gallic acid reagent is used as a simple spot-test to presumptively identify drug precursor chemicals. It is composed of a mixture of gallic acid and concentrated sulfuric acid.

The Zimmermann reagent is used as a simple spot-test used in chromatography to presumptively identify alkaloids, especially benzodiazepines, as well as other compounds. It is therefore used in drugs testing.

<span class="mw-page-title-main">Chen-Kao reaction</span>

The Chen-Kao reaction is a chemical method for determining the presence of pseudoephedrine, ephedrine, and similar phenylalkylamines. The reaction is used in spot tests and is also known as Chen-Kao test. The test is often used to distinguish ephedrine, pseudoephedrine, norephedrine, cathinone and methcathinone from amphetamine and methamphetamine, which do not react with Chen’s test reagent.