Customers often ask, “Should I use serum or plasma for ELISA blood samples?” Today, let’s explore how to choose based on the preparation and differences between serum and plasma.

1. The concept of serum and plasma and the difference between them

Blood drawn from humans or laboratory animals is called whole blood and contains plasma, platelets, and various types of cells such as red blood cells and white blood cells.
Serum is a yellowish transparent liquid precipitated by blood coagulation. If blood is drawn from a blood vessel and placed in a test tube without an anticoagulant, the coagulation reaction is activated and the blood rapidly coagulates to form a jelly-like clot. The clot shrinks, and the yellowish transparent liquid precipitated around it is serum, which can also be obtained by centrifugation after coagulation. In the process of coagulation, fibrinogen is transformed into fibrin clot, so there is no fibrinogen in serum, which is the biggest difference with plasma.
Plasma is to leave the blood vessels of whole blood after anticoagulation treatment (common anticoagulants such as EDTA, sodium citrate, heparin, etc.), through the centrifugation method, so as to obtain the upper layer of the liquid does not contain cellular components, plasma contains fibrinogen (fibrinogen can be converted into fibrin, with coagulation effect).
The coagulation process that produces serum is a process in which coagulation factors are activated in a certain order, eventually transforming fibrinogen into fibrin, fibrin monomers interconnecting to form insoluble fibrin multimers and interweaving with each other to create a net that encompasses the blood cells and ultimately forms a blood clot. Therefore, serum contains no blood cells, no fibrin, and only a few clotting factors (IX, X, Ⅺ, Ⅺ, Ⅺ).
Plasma is the liquid portion that prevents the clotting process from occurring and precipitates the cells by centrifugation, and contains fibrinogen and various clotting factors (normal human plasma contains at least 11 clotting factors in addition to coagulation factor III).
In addition, the concentration of calcium ions in serum is significantly lower than in plasma because calcium ions are also involved in the process of clotting in the body and are consumed during the clotting process.
Other components, such as albumin, globulin, sugars, lipids, vitamins, hormones, and inorganic salts other than calcium ions, are about the same in serum and plasma.
Therefore, when we decide whether to choose serum or plasma samples, it mainly depends on whether the indexes measured are coagulation indexes, and it is better to choose plasma samples if it is coagulation indexes. For other types of indicators, such as cytokines, hormones and other indicators, usually serum or plasma can be.

2. Preparation of serum and plasma prior to ELISA experiments

Serum samples: whole blood was collected in centrifuge tubes. Blood samples were agglutinated for 30 minutes, centrifuged at 1,000 × g for 10 minutes, supernatants were removed and the supernatants were fractionated and stored. -20°C for 1 month. -80°C, stored for 3 months.
Plasma samples: Whole blood was collected in EDTA, sodium citrate, or heparin anticoagulation tubes. 1,000 × g tubes were centrifuged for 30 minutes, supernatants were removed, and the supernatants were fractionated and stored. -20°C for 1 month. -80°C, store for 3 months.

3. Hemolysis of ELISA samples

In addition, we need to avoid hemolysis during ELISA blood sample preparation. Hemolysis, i.e., the rupture of red blood cells in the blood due to various internal and external reasons, the hemoglobin in the red blood cells escapes, resulting in the serum and plasma changing from light yellow to blood red.
During hemolysis, other components of the red blood cells also escape as well, which can have an effect on the levels of some of the test indicators, such as lactate dehydrogenase and creatine kinase, which can be significantly elevated.
In addition, it may be due to the non-specific adsorption of free hemoglobin in the sample onto the enzyme label plate. The ferrous hemoglobin in hemoglobin has peroxidase-like activity, which catalyzes the TMB, the substrate in the last step of the enzymatic reaction of the ELISA, causing false positives.
If hemolysis occurs during the experiment, recollect blood if possible. If it is not possible to recollect blood, only according to their own need to measure the indicators, hemolysis and non-hemolysis samples will be tested against each other to determine whether there is any effect, and whether the results are credible.
As mentioned above, the main difference between serum and plasma is the difference in fibrin and several clotting factors. Coagulation Factors In addition to the 12 major coagulation factors (coagulation factors I, II, III, IV, V, VI, VII, VIII, IX, X, Ⅺ, E.D., Xll. Factor VI is, in fact, an activated Factor V, and the nomenclature of Factor VI has been abolished). In addition, there are coagulation factors.

Mult Science has the following two coagulation factor-related ELISA kits :