With the advent of technology in immunoassays, the pathologist/transfusion medicine specialist is faced with a plethora of choices for his lab./blood bank. Here is a brief monologue on what to chose and what not to. Technologies like CLIA /IFA have an analytical sensitivity in the order IFA>CLIA>ELISA>Rapid tests. What is meant by having a greater analytical sensitivity) The number of positives (both true and false will increase).Paradoxically, this leads to a fall in PPV(TP/TP+FP) for the test.
A decreased PPV (especially in the setting of a diagnostic laboratory)test is of not much use to the clinician. With the existing ELISA, the PPV of a positive test(for HIV) is of the magnitude of 1in 10. Increased analytical sensitivity will lead to a further fall. The PPV of a positive test is calculated by experiments against a reference method or the GOLD STANDARD(in this case the Western…
