An Initiative of the EMRA Research Committee
Terms
Sensitivity: Ability of a test to detect a disease when it is present
Specificity: Ability of a test to detect the absence of a disease
| Disease Positive | Disease Negative | |
| Test Positive | A | B |
| Test Negative | C | D |
Sensitivity= A/(A+C) Specificity= D/(B+D)
Example: The NEXUS cervical spine rule has been shown to have a sensitivity of between 90-99% and a specificity of 36-38%, depending on the source.
What does this mean?
Sensitivity: The NEXUS criteria will be positive for 90-99% of patients who have a cervical spine injury. (Alternately, the NEXUS criteria will be negative for 1-10% of cervical spine injuries in patients who are injured.)
Specificity: The NEXUS criteria will be negative for 36-38% of patients who do not have a cervical spine fracture. (Alternately, the NEXUS criteria will be positive for 62-64% of patients without a cervical spine injury.)
Extra Point: Do NOT use sensitivity or specificity to predict presence or absence of disease. It should only be used to understand the test's characteristics.