Separation of Plasma and Serum from Whole Blood

Introduction

Blood is a vital fluid that circulates throughout the body, delivering oxygen and nutrients to cells and removing waste products. It consists of several components, including red blood cells, white blood cells, platelets, and plasma. Clinical diagnostics often require separating these components, particularly plasma and serum, which provide crucial information about a patient's health status. This page explores the methods and importance of separating plasma and serum from whole blood.

Understanding Whole Blood

Whole blood is the mixture of blood cells and plasma that flows through the circulatory system. It is composed of approximately:

• 55% plasma
• 45% cellular components (red blood cells, white blood cells, and platelets)

What is Plasma?

Plasma is the liquid portion of blood that remains after removing the cellular components by centrifugation in the presence of an anticoagulant. It is a yellowish fluid that contains:

• Water (90-92%)
• Proteins (albumin, globulins, fibrinogen)
• Electrolytes (sodium, potassium, chloride, bicarbonate)
• Nutrients (glucose, amino acids, lipids)
• Waste products (urea, creatinine)
• Hormones
• Clotting factors

What is Serum?

Serum is similar to plasma but differs in that it does not contain clotting factors because it is obtained after blood has been allowed to clot before centrifugation. Serum is essentially plasma without fibrinogen and other clotting factors that have been consumed during the clotting process.

Blood Collection for Plasma and Serum Separation

Proper blood collection is crucial for obtaining high-quality plasma or serum. The following guidelines should be observed:

• Use appropriate collection tubes (tubes containing anticoagulants for plasma, tubes without anticoagulants for serum)
• Ensure proper venipuncture technique to minimize hemolysis
• Gently invert tubes containing anticoagulants to mix the additive with blood
• Label all specimen tubes with patient identification
• Transport specimens to the laboratory promptly

Methods for Separating Plasma

Centrifugation Method

Select Anticoagulants for Plasma

Depending on the clinical test required, different anticoagulants may be preferred:

• EDTA (purple top): Used for hematology and most chemistry tests
• Heparin (green top): Suitable for electrolytes, enzymes, and emergency chemistry tests
• Sodium citrate (light blue top): Required for coagulation studies

Methods for Separating Serum

Standard Method with Clotting

Accelerated Clotting Methods

Several techniques can accelerate the clotting process:

• Using serum separator tubes containing clot activator substances
• Applying gentle heat during the clotting process (maintaining at 37C)
• Adding thrombin or other clotting accelerators in emergency situations

Clinical Applications of Plasma and Serum

Plasma Applications

• Coagulation studies (PT, aPTT, fibrinogen)
• Emergency chemistry tests
• Drug monitoring
• Hormone assays
• Therapeutic drug monitoring
• Blood banking and transfusion medicine

Serum Applications

• Biochemistry profiles (glucose, electrolytes, liver and kidney function tests)
• Serology tests (antibody detection)
• Hormone assays
• Tumor markers
• Cardiac markers (troponin, CK-MB)
• Enzyme assays

Handling and Storage Considerations

Common Interferences and Precautions

• Hemolysis (ruptured red blood cells) can interfere with many tests, particularly potassium and LDH
• Lipemia (high lipid content) can cause turbidity and interfere with spectrophotometric analysis
• Icterus (high bilirubin) can affect colorimetric assays
• Improper centrifugation can result in cellular contamination
• Delayed processing can lead to changes in glucose, potassium, and other unstable analytes

Conclusion

The separation of plasma and serum from whole blood is a fundamental process in clinical laboratories, providing essential diagnostic information. While both plasma and serum contain many of the same analytes, their preparation methods and specific applications differ significantly. Proper collection, handling, and processing of blood samples are critical to obtaining accurate laboratory results. Understanding the distinctions between plasma and serum helps healthcare providers select appropriate tests for patient diagnosis and monitoring.