There are two kinds of sensitivities: analytical sensitivity, and clinical sensitivity.
Analytical sensitivity is all about copy numbers: How many copies would your test need to give a positive result? The more sensitive an assay is, the less copy it will require to yield a positive result.
Clinical sensitivity is all about the patient: when a patient is sick with a disease, how often could your assay give an answer?
People often get these two kinds of sensitivity mixed up. They would say, “when I compare a multiplexed assay, its sensitivity is not as good as a regular real-time PCR.” That maybe true when we talking about analytical sensitivity, but certainly not true when we talking about clinical sensitivity.
Analytical sensitivity is asking the question “if a sample contain a certain molecular target, can your assay detect it?”
Clinical sensitivity is asking the question “if a patient is sick with a disease, can your assay diagnose it?”
Patients do not walk into a clinic with a sticker on the forehead saying “I am sick from the H1N1 influenza virus”, they come in with a group of nonspecific symptoms. The same respiratory symptoms, for example, can be shared by many different infections. A real-time PCR assay, which usually detecting one pathogen at a time, may have 100% analytical sensitivity, but it may totally missed the diagnosis because the target it designed to detect was not the one causing the patient’s illness. In this case, a greater analytical sensitivity does not really help getting an answer.
A multiplex assay may have a lower analytical sensitivity related to a particular target, but the overall clinical sensitivity will be greater because the assay detects more pathogens and gives more answers.
Using regular real-time PCR assays, in order to achieve equal or better clinical sensitivity, the lab would need to run many tests on the same clinical sample to cover as many pathogens as they could. That would cost more and may take longer.
Multiplex assay is desired not only because it save time, but because it may save lives by getting the right diagnosis the first time. When talking about clinical impact, we should put more weight on clinical sensitivity.
* Disclaimer*
Although we may use the words “Diagnosis” or “Diagnostics” in this blog, our products are NOT FDA approved for such uses. We are developing technologies that may eventually have clinical applications, but for now, all our products are for research use only.