Choosing the Right Rapid Test

Screen Italia rapid test COVID

Rapid tests are special because they are used on-site and don’t require complex equipment. The test is usually performed directly on the sample taken, without needing pretreatment. Using a rapid test consists of three steps: sample, analysis and display of results.

• Collection of the test sample: the test only requires a small sample. Depending on the type of test, the type of sample may vary. There are rapid blood tests, rapid urine tests, rapid saliva tests, etc.
• Analysis of the collected sample: the sample is brought into contact with the reagents contained in the test. The composition and mode of analysis of rapid tests vary according to the application and the marker sought.
• Display of results: after a few minutes, the test usually indicates whether the result is positive (the marker has been found in the sample) or negative.

Teco Diagnostics rapid syphilis test

Rapid tests have many applications in the medical, environmental, legal and food industries.

• The medical field: rapid tests are used for the diagnosis of various diseases, including rapid tests for infectious diseases. These tests are for specific markers whose presence in the sample confirms the existence of the disease. There are also tests to confirm a particular condition, such as pregnancy tests or ovulation tests.
• The environmental field: some rapid tests can be used to analyze the quality of water or air, for example, by means of samples collected at a given site.
• The legal field: many rapid tests are used to detect the presence of illegal substances in the body (rapid toxicology tests) or to measure blood alcohol levels.
• The food industry: in this field, rapid tests are used for product quality control. Rapid tests for food safety make it possible, for example, to identify counterfeit products or those likely to pose a danger to consumer health.

Operon rapid test for infectious diseases

There are several analysis methods that can be used to detect the presence of a specific marker in a sample. The main ones are immunological rapid tests, molecular tests and colorimetric rapid tests.

• Immunological rapid tests (immunoassays): these tests will determine the presence of a marker via a biochemical reaction involving immune proteins (antibodies or antigens). There are several types of immunoassays depending on the reaction performed:
  • Enzyme immunoassays
  • ELISA (Enzyme Linked ImmunoSorbent Assay)
  • Lateral flow tests (immunochromatographic).

• Molecular tests: in the case of a molecular test, the reaction is determined by the presence of genetic material specific to the marker sought. There are different types of molecular tests that differ in the technique used. The main ones are:
  • PCR tests
  • RT-PCR tests
  • QF-PCR tests

• Rapid colorimetric tests For colorimetric tests, the result of the reaction is determined by the color obtained. In general, a color is produced identically for a class of compounds. It should be noted, however, that colorimetric tests are an indication of the presence of a compound or class of compounds in a sample, but that they must be confirmed by more specific methods, particularly in the case of forensic medicine.

There are many rapid test brands on the market. Their respective performances are generally measured against a “gold standard” reference. The latter may be a reference standard examination or an expert opinion to categorize patients as “well” or “unwell”. The evaluation is based on two indicators: the test’s intrinsic and extrinsic validity.

• The test’s intrinsic validity: this is the ability of the test to estimate whether the disease is present. It is evaluated by:
  • Test sensitivity (true positive rate)
  • Test specificity (true negative rate)
• Extrinsic test validity: this is linked to the characteristics of the population tested. It is based on the prevalence of a given disease in a population group. Predictive validity is another factor. It is defined by the positive or negative predictive values of the test for a given population.

Even though rapid tests make it possible to avoid a number of factors that are often synonymous with errors (sample management, complex equipment, etc.), it is still important to take precautions. In the context of tests carried out by professionals, two essential precautions are staff training and personal protection.

• Staff training: staff must be trained in the sampling procedure (procedures to be carried out, equipment to be used, etc.) as well as in the interpretation of results. Depending on the type of test to be carried out and the test brand, the procedure and results reading method may vary, or even diverge.
• Staff personal protection: in the case of tests for contagious diseases, the personnel performing the sampling and testing must have adequate protective equipment (mask, gloves, etc.). This is essential not only to prevent the health care staff from being contaminated but also to prevent the sample itself from being contaminated.