I was reading about diagnostic tests for sepsis on www.pulmccm.org just now. Excellent site to keep yourself up-to-date on all matters Pulmonary and Critical Care, by the way. It's discussing the Septicyte Rapid and the Intellisep proprietary tests. See link above for the article. These tests are technology looking for an indication and cash flow, as unfortunately so many are. Let me tell you a little secret about the studies cited that are purported to support the diagnostic utility of these tests.
Ignore Any Report of +/- Predictive Value of a Diagnostic Test.
If you know that, and to look instead for the sensitivity and specificity of the test, you can just memorize my rule and move on to your next task of self-edification today. But if you want to understand why, read on.
The predictive value (+ or -) of a test depends on sensitivity and specificity of the test and the "prevalence" of the disease under consideration in the tested population. If you're trying to understand a test, you don't care about the prevalence of disease in that population, because it may not reflect the prevalence in your population of interest. Sensitivity and Specificity are the measures of the test itself, in isolation. So whenever you see positive and negative predictive value reported, you can bet your arse that it's because the either low or high prevalence of disease in the test population made the PPV (positive predictive value) and NPV (negative predictive value) look better than the sensitivity and specificity.
