Serum is the supernatant fluid when clotted blood has been centrifuged. It is the best specimen for most clinical chemistry laboratory tests because of its specific characteristics. Here are the reasons why serum is the best specimen.
*Serum has less protein
When blood clots, one of the proteins - fibrinogen - takes part in the clotting process; thereby removing it from the serum. The absence of fibrinogen would make the supernatant clearer, while in plasma, since the blood does not clot, the fibrinogen remains in the supernatant and could add to the turbidity of the plasma.
*Serum has no anticoagulant
Since serum does not have an anticoagulant, there are no other substances that could interact with your test. There are potential interferences coming from anticoagulants with certain tests. One example is the interference of the anticoagulant ethylene diaminetetraacetic acid (EDTA) in the laboratory determination of calcium ions. EDTA chelates calcium; hence, decreasing inaccurately the concentration of calcium in the sample.
The presence of an anticoagulant could also dilute the specimen and unreliably lower the concentration of the substance being analyzed.
*Most reagents are more compatible with serum
The optimum reaction of the reagent with the substance in the blood is very important to produce reliable results; results that are precise and accurate simultaneously. When a result is precise, it means that you get almost the same results repeatedly. Accuracy on the other hand, means obtaining values close to the “true value.” When a result or method is reliable, then you are certain of the results because you know they could be depended on.
Laboratory results are the data that doctors could base their diagnosis on. Together with the history of the patient, the other diagnostic results, doctors could now come up with a conclusive diagnosis.
*Serum can be more stable than plasma with certain substances
Some research like the study done by O'Keane and Cunningham proved that serum is more stable for other substances than plasma. This is most especially for serum extracted with a separator gel. Gel tubes proved to be stable for creatinine, potassium, and urea than in plasma. This would specify that gel tubes are more stable that plain serum tubes.
These are the reasons why serum is considered the best specimen. This does not indicate though, that the other blood specimens could not be used. There are certain tests, which require, specifically a plasma sample or a whole blood sample. Knowing what these tests are would help a lot in coming up with reliable results and a correct diagnosis by the doctor.