Is sensitivity the proportion of individuals with disease who test positive (true‑positive rate) and specificity the proportion of individuals without disease who test negative (true‑negative rate)?

Understanding Sensitivity and Specificity

Yes, you are correct: sensitivity is the proportion of individuals with disease who test positive (true-positive rate), and specificity is the proportion of individuals without disease who test negative (true-negative rate). 1, 2

Core Definitions

Sensitivity measures how well a test catches disease when it is actually present:

• Calculated as True Positives / (True Positives + False Negatives) 2
• Represents the percentage of diseased patients correctly identified by the test 1, 2
• Answers the question: "Of all the people who actually have the disease, what percentage will test positive?" 1

Specificity measures how well a test correctly identifies those without disease:

• Calculated as True Negatives / (True Negatives + False Positives) 2
• Represents the percentage of disease-free patients correctly labeled as negative 1, 2
• Answers the question: "Of all the people who do not have the disease, what percentage will test negative?" 1

The Inverse Relationship

Sensitivity and specificity are inversely related—when one increases, the other decreases: 1

• As you adjust the diagnostic cutoff to catch more true cases (increasing sensitivity), you inevitably catch more false positives (decreasing specificity) 1
• All diagnostic tests have a range of inversely related sensitivities and specificities that can be selected by choosing different diagnostic cutoff points 1
• For example, exercise ECG testing using 1mm ST-segment depression demonstrates sensitivity of 68% and specificity of 77% for coronary artery disease, but these values would shift if a different cutoff were chosen 1

Factors That Influence These Metrics

Sensitivity is influenced by: 1

• Disease severity (tests perform better with more severe disease) 1
• Patient effort level during testing 1
• Use of anti-ischemic drugs or other medications 1

Specificity can be affected by: 1

• Medications such as digoxin 1
• Baseline electrocardiographic patterns 1
• Left ventricular hypertrophy 1

Critical Distinction from Predictive Values

Sensitivity and specificity are characteristics of the test itself, not measures of disease probability in individual patients: 2

• These metrics remain constant regardless of disease prevalence in the population 2
• In contrast, positive predictive value (PPV) and negative predictive value (NPV) tell you the probability that a patient actually has or doesn't have disease given their test result 2
• PPV and NPV vary dramatically with disease prevalence, while sensitivity and specificity do not 2