Sensitivity vs. Specificity
Whats the difference and why do we care?
Interpreting lab values can seem complex. You may notice a value is high or low, but what does that mean to you clinically? Just how accurate is the test, and can a positive or negative result mean more than one thing? When interpreting lab values its important to remember all tests can be evaluated in terms of Specificity and Sensitivity.
Sensitivity measures how likely the test will produce a false positive or false negative. If a test has a high likelihood of reporting a false positive or negative it has a low sensitivity.
Specificity, on the other hand, measures how likely the finding of the test relates to the specific condition you’re testing for (for example a high ALT is highly specific for liver damage. It will be raised for almost no other reason vs. Troponin which will be elevated in cases of an acute MI but also elevated due to other non-cardiac related conditions, such as renal failure).
Understanding false positives, false negatives, and the likelihood of each will help you better interpret the significance of lab values.