What Is the Difference Between Plasma and Serum?

Updated on August 1, 2020
Sherry H profile image

Sherry Haynes is currently pursuing a PharmD degree and has experience in both the clinical and management sides of pharmacy.

Plasma vs Serum
Plasma vs Serum

Blood is not always used directly for testing in a lab; rather it is the plasma or serum portion of the blood.

When the blood is left in a test tube with an anticoagulant, it sediments. The blood cells having a higher density occupy the lower portion of the test tube and the lighter part that is the plasma occupies the upper portion.

Therefore, one can say that the blood plasma = whole blood - blood cells.

Similarly, when the blood is left undisturbed in a test tube (without an anticoagulant), it clots. Within a few minutes after the clot is formed, it begins to contract and ooze out most of the fluid within 30-45 minutes. The fluid oozed out is called serum.

The blood clot consists of all the blood cells, fibrinogen, and a few other clotting factors. The remaining portion in the test tube is the serum.

Accordingly, serum = whole blood - (blood cells + fibrinogen and clotting factors II, V, VIII)

Summary of the Differences Between Serum and Plasma

  1. Plasma is blood without cells whereas serum is the remaining plasma after coagulation.
  2. Anticoagulant is needed for the seperation of plasma, while no anticoagulant are required for the seperation of serum.
  3. Plasma contains coagulation factors II, V, and VIII and fibrinogen while serum lacks these factors.
  4. Plasma has comparatively higher concentration of proteins than serum.
  5. Plasma is obtained within a shorter period of time as the clotting time is eliminated whereas a waiting time of 35-45 minutes before centrifugation is necessary to obtain serum.
  6. 15-20% more yield of plasma is obtained compared to serum.
  7. There is a lower risk of haemolysis and thrombolysis in plasma compared to serum.
  8. Post-centrifugation coagulation can occur in serum whereas it does not occur in plasma.

Apart from these, the two specimens also differ in their usefulness as well as the alnalyte composition. (Refer table 1 and 2 in this article).

Concept

Plasma = whole blood - blood cells

Plasma = whole blood - (red blood cells + white blood cells + platelets)

Serum = whole blood - (blood cells + clotting factors)

Serum = whole blood - (red blood cells + white blood cells + platelets + fibrinogen, clotting factors II, V, VIII)

Serum = Plasma - (Fibrinogen + Clotting factors II, V, VIII)

The Coagulation Process Makes Serum Different From Plasma

To understand the differences, you must be aware of how the plasma and serum are seperated from whole blood. The following steps explain what laboratories do to get these specimens.

1. Blood is drawn from the patient.

Blood samples for lab testing may be obtained in several ways. The most common procedure is venipuncture, withdrawal of blood from a vein using a needle and a collecting tube, which contains various additives.

A tourniquet is wrapped around the arm above the venipuncture site, which causes blood to accumulate in the vein. This increased blood volume makes the vein stand out, making venipuncture more successful.

To ensure that there is no confusion on the part of the phlebotomist in identifying the proper tube, the stoppers and closures of collecting tubes are colour-coded. For example, the stopper of collecting tube containing the additive EDTA (an anticoagulant) is lavender. This tube is used when you want to mix the blood with the anticoagulant EDTA to get plasma.

Conversely, if you want to obtain serum you need to have the blood clot so you don't want to use the tube with an anticoagulant. Therefore, the collecting tube to get serum is plain, colour-coded red. Similarly, there are various colour-codes for anticoagulant as well as other additives such as a preservative.

Blood drawn from a patient.
Blood drawn from a patient. | Source

2. The collecting tubes are centrifuged.

The tube with anticoagulants can be spun immediately to obtain plasma. Whereas, the tube for serum must be stored for 30-45 minutes undisturbed, and, preferably, in the dark before centrifugation.

Separation mechanism

Whole blood in a collecting tube with anticoagulants get you plasma after centrifugation. This is because the coagulability of the blood is inhibited by the addition of anticoagulants.

The heavier portion of the whole blood, the red blood cells settle at the bottom of the test tube. Then, the next layer is the buffy coat consisting of white blood cells and platelets. Plasma is virtually the remaining cell-free supernatant.

Whole blood in a plain collecting tube will give you serum after centrifugation is done 30-40 minutes post-blood collection. The standing time of 40 minutes is given to allow the blood to clot. This clot then contracts to ooze out the serum. Initially, the clot is the whole blood then after some time, it starts to release the fluid portion of it which is plasma except fibrinogen. There is no fibrinogen in the serum because it is converted into fibrin during the formation of the clot.

Laboratories use gel separators to improve the yield of specimens. The gel in a separator tube is a liquid polymer along with an organic or inorganic filler added to achieve the appropriate density of the gel.

Serum separated from blood by a gel layer. The red appearance in the first tube is because of a bad draw. The second tube shows normal serum after a perfect draw. The brownish yellow appearance in third tube shows liver issues.
Serum separated from blood by a gel layer. The red appearance in the first tube is because of a bad draw. The second tube shows normal serum after a perfect draw. The brownish yellow appearance in third tube shows liver issues. | Source
Plasma seperated after centrifugation. On seeing closely, you can observe a layer in the middle called buffy coat. It consists of white blood cells and platelets.
Plasma seperated after centrifugation. On seeing closely, you can observe a layer in the middle called buffy coat. It consists of white blood cells and platelets.
Serum immediately after centrifugation. In this, gel separator is not used hence you don't see a gel layer in the middle.
Serum immediately after centrifugation. In this, gel separator is not used hence you don't see a gel layer in the middle. | Source

3. The specimen is separated for analysis.

Next step after centrifugation is to transfer the samples (plasma or serum) directly to the analyzer. Ideally, the analyzer need does this job by piercing the closed stopper and collecting thereby.

Manually, the plasma or serum is recollected using a transfer pipette. It is done carefully without disturbing the other layers into another labelled tube.

Analytes Concentration in Serum Compared with Plasma

Analyte
Concentration in serum compared to plasma
Reason for the change
Fibrinogen, platelets and glucose
Low
These analytes are consumed during clotting in the serum.
Potassium, phosphate, ammonia, lactate dehydrogenase
High
These analytes are released from cells during clotting.
Total protein
Low
Removal of a large portion of the fibrinogen content of plasma in the form of fibrin clot results in this.
Table 1

Blood Tests and Specimen Used

Serum
Plasma
Whole Blood
Alanine amino transferase (ALT) and aspartate amino transferase (AST)
Ammonia
Carbondioxide content
Bilirubin
Cholesterol (total, HDL, LDL)
Hemoglobin
Blood urea nitrogen
Electrolytes
Platelet count
Creatine
Glucose
RBC count
Creatinine
 
WBC count
Creatinine Phosphokinase (CPK)
 
 
Iron
 
 
Lactate dehydogenase
 
 
Lipids (total, triglycerides)
 
 
Proteins (total, albumin, globulin)
 
 
Uric acid
 
 
Table 2: In addition to these tests, serum is useful for testing hormones, in enzyme assays, and blood grouping. Plasma is useful in transfusion and plasma therapy.

Misconceptions About Serum vs Plasma

1. The serum does not contain clotting factors.

This is false since clotting factors IX, X, XI, and VII/VIIa are found in serum.

2. Plasma is liquid and serum is fluid.

This statement can be true if you are talking about serum as it oozes from the clot. But, to say that the plasma is liquid and serum is fluid is technically wrong considering the definition of fluid and liquid.

References

  1. Guder, W. G., Narayanan, S., Wisser, H., & Zawta, B. (2008). Samples: from the patient to the laboratory: the impact of preanalytical variables on the quality of laboratory results. John Wiley & Sons.
  2. Tortora, G. J., & Derrickson, B. H. (2018). Principles of anatomy and physiology. John Wiley & Sons.
  3. Issaq, H. J., Xiao, Z., & Veenstra, T. D. (2007). Serum and plasma proteomics. Chemical reviews, 107(8), 3601-3620.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2020 Sherry Haynes

Comments

    0 of 8192 characters used
    Post Comment
    • Miebakagh57 profile image

      Miebakagh Fiberesima 

      7 weeks ago from Port Harcourt, Rivers State, NIGERIA.

      So do I.

    • Eurofile profile image

      Liz Westwood 

      7 weeks ago from UK

      This is an interesting and well-explained article. I have learnt a lot from it.

    working

    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, owlcation.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://maven.io/company/pages/privacy

    Show Details
    Necessary
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
    Features
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Marketing
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Statistics
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)
    ClickscoThis is a data management platform studying reader behavior (Privacy Policy)