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 two main considerations here and thats volume required for analysers and how the analysers detect analytes.
Most medical tests are done using spectrophotography which involves firing a beam of light through a sample that’s been mixed with a reagent and measuring the change in wavelength of the light through the sample over time. The reagent used typically binds to whatever analyte your looking at measuring, for example CRP, so you’ll need to use a different analyte and a different sample for every individual test you want to do.
Analysers have different methods of doing this off a single sample, the one I used to work on had a carousel, your sample would sit in the back of the machine on a belt and a little pipette on an automated arm would suck up the tiny amount of sample and deposit in a bit of the carousel. It would do the reaction in there and measure it and clean it out. This process doesn’t really need much sample however the arm that takes those little samples uses fluid measurement to know how far to go down into the tube. What this means is you need a “dead volume” which is the minimum the arm can detect. If your blood bottle has only a tiny amount the arm will hit the bottom of the tube and break. For this reason, if there’s lots of tests being done we need multiple bottles.
If your talking about the different colour bottles that’s a whole different thing. Most biochemistry and serology analytes are done using serum (normally a gold coloured top in the UK), this is when you take blood then spin it down to remove all the red blood cells after they have been allowed to clot. We do this because red blood cells and big and get in the way of that spectrophotography j mentioned earlier and unless we are measuring them directly there’s no need to have them in there. Many of the tests on your form will be done using serum or plasma, which is the same as serum in its spun down but anticoagulant is added first as whatever we are measuring gets gunked up in the clot otherwise.
Then you’ll have tubes like EDTA (purple top in the UK) these contain an anticoagulant to stop clotting and stablise the red blood cells. This is used for blood counts which are vitally important and are measured usually through a different mechanism, the way we used to do it was flow cytometry which is firing a sample through a water pistol with a nozzle so thin only one cell can fit through at a time and firing lasers at it.
There are other less used tubes then but it’s all about the stability of the sample and if you can allow the sample to clot without losing whatever analyte your looking for. Also it depends on the mechanism used to measure it, although spectrophotometry is common for alot there are other methods that require different stabilisers and anticoagulants.
Latest Answers