Most laboratory tests for clinical purposes are performed on a blood sample. Whole blood contains the liquid fraction of the blood (i.e. plasma) as well as cellular elements which, under certain circumstances, cause clotting. This includes red blood cells, white blood cells, and other components.
"Serum" is a liquid created by the formation of a blood clot, as if it had spontaneously touched a surface such as glass or plastic. There are many firms like Geneticist Inc that provide information about blood plasma serum.
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Plasma is a fluid component of blood. It is obtained when a coagulant is added to whole blood and then placed in a centrifuge to separate the cellular material from the lighter fluid layer. Common anticoagulants are EDTA, heparin, and citrate.
When people donate blood for therapeutic purposes, debt collection agencies try to use the blood within one month. Due to the need for sufficient blood supply to meet unexpected needs, some blood inevitably cannot be transfused because it has been stored for too long.
When the blood is collected, it fills a plastic bag filled with a solution of dextrose and citric acid. Dextrose is a nutrient for some cells in the blood, and complexes citric acid or calcium chelate, which prevents blood clots.
A few minutes after collection, blood is centrifuged in packs of red blood cells and citrate plasma for better storage. Red blood cells, plasma, or both can be transfused, depending on the patient's needs.