ELISA Assay Sample Selection: Serum or Plasma?
When conducting ELISA experiments, many researchers face a dilemma: whether to use serum samples or plasma samples for detecting indicators? In fact, the answer to this question is closely related to the type of indicator being tested.
In general, plasma is the best choice for detecting coagulation-related indicators, while serum is preferable for detecting immune-related indicators. For other types of indicators, including changes in cytokines, both serum and plasma can usually be used. Let's delve into the reasons behind this.
Differences Between Serum and Plasma
Serum and plasma differ in composition, and these differences determine their applicability in various detection scenarios.
· Serum contains no fibrinogen, certain coagulation factors, or plasma proteins involved in coagulation, but it does contain some substances released by platelets during the coagulation process.
· Plasma contains fibrinogen (which can be converted into fibrin and has a coagulative effect) and coagulation factors, but lacks the substances released by platelets during coagulation.
Tips: Plasma can be converted into serum by removing fibrinogen and other coagulation factors.
Based on these compositional differences, their application scenarios are also distinct:
· Serum is mostly used in blood biochemistry, immunology, and other related detections;
· Plasma is mostly used in coagulation and other related detections;
· Whole blood is mostly used in blood cell, blood routine, erythrocyte sedimentation rate, and other related detections.
Serum and Its Main Components
Serum refers to the pale yellow transparent liquid separated from plasma components after blood coagulation, excluding fibrinogen, certain coagulation factors, and does not contain blood cells (including platelets) and other components.
Its main components include:
· Serum proteins: total protein, albumin, α1, α2, β, γ-globulins, etc.;
· Carbohydrates: glucose, fructose, galactose, mannose;
· Lipids: total cholesterol, triglycerides, β-lipoprotein, HDL cholesterol;
· Serum enzymes: GOT, GPT, γ-GTP, LDH (lactate dehydrogenase), amylase, alkaline phosphatase, acid phosphatase, cholinesterase, aldolase;
· Hormones: thyroid-stimulating hormone, thyroid hormones;
· Pigments: bilirubin, indocyanine green (ICG), sulfobromophthalein sodium (BSP);
· Organic salts: creatinine, urea nitrogen, uric acid, creatinine clearance;
· Electrolytes: sodium (Na), potassium (K), calcium (Ca), chlorine (Cl).
Plasma and Its Main Components
Plasma is an important component of blood. It is the pale yellow transparent liquid obtained by separating all blood cells (including platelets) from whole blood after anticoagulation treatment via centrifugation.
Its main components include:
· Plasma proteins: which can be divided into albumin, globulin, fibrinogen, etc.;
· Non-protein nitrogen: urea, uric acid, creatinine, amino acids, polypeptides, ammonia, bilirubin, etc.;
· Inorganic salts: most of the inorganic substances in plasma exist in ionic form, such as: Na+, K+, Ca2+, Mg2+, Cl-, HCO3-, HPO42-, SO42-, etc.
Advantages and Disadvantages of Serum and Plasma in Pharmacokinetic Research
In pharmacokinetic research, serum and plasma each have their own advantages and disadvantages:
· Plasma contains anticoagulants (EDTA or heparin), which may interfere with the binding or detection of compounds, while serum does not have this problem;
· Plasma preparation is rapid, as it can be separated directly after low-temperature centrifugation, whereas serum preparation takes longer. This has a significant impact on pharmacokinetic tests because blood sampling points are usually 密集 within 4 hours after administration;
· The coagulation process of serum may cause adsorption with drugs, thereby reducing the drug content in serum and leading to experimental errors.
Preparation Methods of Serum and Plasma
Preparation of Serum Samples
· Collect blood samples using pyrogen-free and endotoxin-free test tubes or centrifuge tubes. Place the test tubes or centrifuge tubes at room temperature for 1 hour or at 2-8°C overnight to allow blood coagulation and separate serum;
· Centrifuge at 1000×g for 20 minutes at 2-8°C, and carefully collect the upper serum.
Preparation of Plasma Samples
· Collect blood samples using blood collection tubes or centrifuge tubes containing anticoagulants. Within 30 minutes after collection, centrifuge at 1000×g for 15 minutes at 2-8°C, and carefully collect the upper plasma;
· Common anticoagulants include EDTA sodium salt, heparin sodium, sodium citrate, etc. In ELISA experiments, EDTA salts (EDTA-Na2 or EDTA-K2) are usually recommended as anticoagulants.
In general, plasma is the best choice for detecting coagulation-related indicators, while serum is preferable for detecting immune-related indicators. For other types of indicators, including changes in cytokines, both serum and plasma can usually be used. Let's delve into the reasons behind this.
Differences Between Serum and Plasma
Serum and plasma differ in composition, and these differences determine their applicability in various detection scenarios.
· Serum contains no fibrinogen, certain coagulation factors, or plasma proteins involved in coagulation, but it does contain some substances released by platelets during the coagulation process.
· Plasma contains fibrinogen (which can be converted into fibrin and has a coagulative effect) and coagulation factors, but lacks the substances released by platelets during coagulation.
Tips: Plasma can be converted into serum by removing fibrinogen and other coagulation factors.
Based on these compositional differences, their application scenarios are also distinct:
· Serum is mostly used in blood biochemistry, immunology, and other related detections;
· Plasma is mostly used in coagulation and other related detections;
· Whole blood is mostly used in blood cell, blood routine, erythrocyte sedimentation rate, and other related detections.
Serum and Its Main Components
Serum refers to the pale yellow transparent liquid separated from plasma components after blood coagulation, excluding fibrinogen, certain coagulation factors, and does not contain blood cells (including platelets) and other components.
Its main components include:
· Serum proteins: total protein, albumin, α1, α2, β, γ-globulins, etc.;
· Carbohydrates: glucose, fructose, galactose, mannose;
· Lipids: total cholesterol, triglycerides, β-lipoprotein, HDL cholesterol;
· Serum enzymes: GOT, GPT, γ-GTP, LDH (lactate dehydrogenase), amylase, alkaline phosphatase, acid phosphatase, cholinesterase, aldolase;
· Hormones: thyroid-stimulating hormone, thyroid hormones;
· Pigments: bilirubin, indocyanine green (ICG), sulfobromophthalein sodium (BSP);
· Organic salts: creatinine, urea nitrogen, uric acid, creatinine clearance;
· Electrolytes: sodium (Na), potassium (K), calcium (Ca), chlorine (Cl).
Plasma and Its Main Components
Plasma is an important component of blood. It is the pale yellow transparent liquid obtained by separating all blood cells (including platelets) from whole blood after anticoagulation treatment via centrifugation.
Its main components include:
· Plasma proteins: which can be divided into albumin, globulin, fibrinogen, etc.;
· Non-protein nitrogen: urea, uric acid, creatinine, amino acids, polypeptides, ammonia, bilirubin, etc.;
· Inorganic salts: most of the inorganic substances in plasma exist in ionic form, such as: Na+, K+, Ca2+, Mg2+, Cl-, HCO3-, HPO42-, SO42-, etc.
Advantages and Disadvantages of Serum and Plasma in Pharmacokinetic Research
In pharmacokinetic research, serum and plasma each have their own advantages and disadvantages:
· Plasma contains anticoagulants (EDTA or heparin), which may interfere with the binding or detection of compounds, while serum does not have this problem;
· Plasma preparation is rapid, as it can be separated directly after low-temperature centrifugation, whereas serum preparation takes longer. This has a significant impact on pharmacokinetic tests because blood sampling points are usually 密集 within 4 hours after administration;
· The coagulation process of serum may cause adsorption with drugs, thereby reducing the drug content in serum and leading to experimental errors.
Preparation Methods of Serum and Plasma
Preparation of Serum Samples
· Collect blood samples using pyrogen-free and endotoxin-free test tubes or centrifuge tubes. Place the test tubes or centrifuge tubes at room temperature for 1 hour or at 2-8°C overnight to allow blood coagulation and separate serum;
· Centrifuge at 1000×g for 20 minutes at 2-8°C, and carefully collect the upper serum.
Preparation of Plasma Samples
· Collect blood samples using blood collection tubes or centrifuge tubes containing anticoagulants. Within 30 minutes after collection, centrifuge at 1000×g for 15 minutes at 2-8°C, and carefully collect the upper plasma;
· Common anticoagulants include EDTA sodium salt, heparin sodium, sodium citrate, etc. In ELISA experiments, EDTA salts (EDTA-Na2 or EDTA-K2) are usually recommended as anticoagulants.
