Difference Between Blood Plasma & Blood Serum


Human blood is comprised of many elements, and over half the blood in the body is comprised of liquid plasma or serum. These substances are similar and collected using the same method, but specimens are separated utilizing specially designed collection tubes that extract only serum or plasma. Samples may be used for specific medical testing and to identify medical abnormalities. The physical appearance of a specimen can also indicate potential health problems, even prior to testing.


Collection is performed using specialized plasma separator, plasma preparation and serum separator tubes. A centrifuge is used to separate the plasma or serum from the whole blood components, including red and white blood cells. After centrifugation is completed, the heavier whole blood cells settle to the bottom of the specimen tube, with the plasma or serum at the top. The required sample is pipetted or poured off into additional tubes for testing.

Blood Plasma

Healthy plasma appears as a light yellow, translucent liquid. Human blood is composed of approximately 55% plasma, and plasma is composed of 90% water. The remaining 10% contains minerals, hormones, electrolytes, waste products and nutrients to provide energy for the body. Also, it transports essential gasses throughout the body, including oxygen, carbon dioxide, and nitrogen.

Blood Serum

Normal serum is identical in appearance and composition to plasma, containing the same levels of minerals and water. The difference is a clotting factor called fibrinogen, which is lacking in a serum sample. Abnormal serum samples may appear milky, cloudy or deep yellow in color indicating potential health problems, such as high cholesterol and jaundice.


Only found in blood plasma, fibrinogen is a critical element required for the body to begin the clotting process. Without this element the body has no ability to contain bleeding and abnormal levels can result in clotting disorders, with the most commonly associated medical condition being hemophilia. Disorders of this nature are often treated by plasma donations and medical treatment can vary based on condition and severity.

Testing Blood Plasma and Serum

Some medical testing is specific to serum or plasma, while other testing can be performed on either specimen. Coagulation or clotting tests, ammonia and potassium testing can only be performed on plasma due to the presence of fibrinogen, or the clotting process.