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
medical lab professional here
some tests are done on serum, some plasma, some whole blood that has been prevented from clotting.
The different coloured tubes contain different chemicals. Most of them are to prevent clotting. If I were testing you for a CBC (complete blood count), it would include things like the number of white blood cells per litre of blood. We would not be able to count them if the white cells were trapped in a blood clot (like a net). Also, sucking up small bits of clot might clog up my analyzer and cause it to go down.
One easy-to-understand example of having to have the right tube to have the right sample for a particular test is: grey top is potassium oxalate anticoagulant. How could I tell how much potassium is in your blood, if there is potassium (ox) in the tube before your blood even goes in?
Some tests also require very strict standards regarding the ratio of blood to anticoagulant in the tube (chemical to stop clotting). If you were on coumadin (blood thinner) and I was testing your INR to ensure the amount of coumadin you were taking was keeping you in the INR’s therapeutic range, then the tube would need to be at minimum 95% full of blood. Any less than that and I have to reject the sample. Similarly if the collection was difficult, or performed poorly, and the blood cells lyse (break apart), then the contents of the blood cells will change the amount of different substances in your serum or plasma. For example, red blood cells contain a lot of potassium. If the red blood cells were lysed, they’d release their potassium (etc.) into the serum or plasma making it impossible to tell how much potassium is in your serum or plasma. Imagine an icecube made of orange juice that you put in a glass of water. I’m comparing the icecube to the red blood cells – as the ice melts, or the red cells lyse, they release their contents into the surrounding fluid.
Medical lab professionals study long and hard to know how to get physicians accurate results. Most of the time, nurses and physicians do not have the same specialized knowledge as we do. Sometimes they pressure us to run an inadequate sample. However, a wrong result can be very harmful.
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