How to be sure that a Rapid Diagnostic Test is reliable?

Professional Rapid Diagnostic Test Chlamydia

Professional Rapid Diagnostic Tests (RDTs) are great tools to have when you need a fast and reliable diagnostic solution at the point-of-care.
To enable assessment of their reliability you need to have the sensitivity & specificity, which determine accuracy. Understanding some basic definitions can minimize being misled by false-negative or false-positive results. 1,2

SENSITIVITY (True positive rate): Proportion of people WITH condition that test POSITIVE. A test with 100% sensitivity means all individuals with the condition are correctly identified, i.e. there are no false negatives.
False negative = 100% – Sensitivity

SPECIFICITY (True negative rate): Proportion of people WITHOUT condition that test NEGATIVE. A test with 100% specificity means all healthy individuals are correctly identified as healthy, i.e. there are no false positives.
False positive = 100% – Specificity

Important to note: tests (RDTs or lab tests) are never 100% accurate (100% sensitivity & 100% specificity).
Therefore, looking at these main parameters when doing/requesting a diagnostic test is essential to understand its reliability.

Positive and Negative Predictive Values can also be evaluated if you know the prevalence of the condition in the population that is being tested.

How to Minimize False Results? 3,4

  • Use rapid diagnostic tests with high sensitivity and specificity (at least >90%)
  • Choose a test with false positive rate less than 10%
  • Follow manufacturer’s instructions to ensure correct collection of the specimen

 

Want to know more about the current range of Professional Rapid Diagnostic Tests available, CLICK HERE

References:

  1. Cochrane UK (https://uk.cochrane.org/news/sensitivity-and-specificity-explained-cochrane-uk-trainees-blog
  2. Abdul Ghaaliq Lalkhen, Anthony McCluskey, Clinical tests: sensitivity and specificity, Continuing Education in Anaesthesia Critical Care & Pain, Volume 8, Issue 6, December 2008, Pages 221–223. https://doi.org/10.1093/bjaceaccp/mkn041
  3. CDC, 2019, Information for Clinicians on Rapid Diagnostic Testing for Influenza. https://www.cdc.gov/flu/professionals/diagnosis/rapidclin.htm
  4. WHO, 2019, Rapid diagnostic tests, https://www.who.int/malaria/areas/diagnosis/rapid_diagnostic_tests/en/