Why can’t a single blood test show you all the information you need instead of having to take multiple tests for different markers?
In: Biology
There are quite a few reasons why you don’t test for every marker on every patient, and if the question is why there is no “universal test”, it gets even trickier.
***Cost:*** for each marker you want to test for, you need a specific reagent that reacts with the components of your blood in a very specific way. If you tested for literally everything on everyone every time, the sheer amount of reagents used would counter any proposed benefit in simplicity. Testing for syphilis on literally every patient would be extremely wasteful, and even more so if you did it every day on every patient who ever had prolonged hospital stay.
***Overlap in reading areas (wavelengths):*** If what you’re asking for is why there is no “universal analysis” that just reads every substance at the same time, there are many reasons. One of which is that a lot of tests are interpreted based on how the sample interacts with light. You add a reagent, which leads to the formation of a compound which reacts in a special and predictable way with light at a certain wavelength. Some other substances are part of reaction chains that are read at the same wavelength, so if you then had a signal spike, it’d be impossible to know which of those substances were the cause. All you’d be able to say is that the concentration of A and B combined is X, but that would be of no use. That is one of the reasons why analyses have to be separated into specific tests for specific substances, so that there is no interference from the other tests being done simultaneously. It’d be a very unfortunate situation to be in to have to say “your rash is either because of allergies or syphilis. We’re not exactly sure which, because we ran the tests at the same time”.
***Tube additives:*** the tests used for analysis have special additives that, among other things, affect how blood coagulates. Some analyses, like cell counts, require a sample that has not been coagulated at all so you can count and differentiate the cells. Other tests need all cells removed, because the presence of cells can over time contaminate a sample (the concentration of potassium inside of cells is 30 times higher than the concentration outside of them). When you have different tests that simultaneously require the removal of- and the inclusion of cells, it gets hard to have one universal tube, let alone an universal test.
There are a ton of other good reasons, but the response is already longer than I wanted. A comprehensive list or explanation for why would just be too dang long to write or read.
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