It found to be the same for dogs blood,

Bennett, Mary A. "A COMPARISON OF THE pH OF SERUM AND PLASMA OF DOG BLOOD." Journal of Biological Chemistry 69.2 (1926): 693-696.‏

APA

I am not sure if that applies to humans,

Dear Elodie,

I hope that following publication (in human) will be helpful.

http://www.clinchem.org/content/35/8/1722.full.pdf

 Thanks for your helpful answers

Plasma is a colloidal fluid of complex composition containing numerous components. It covers 55% of blood volume. It consists of 91.5% water and numerous inorganic and organic substances (solutes plasma). .The PH of the plasma is close to 7.40. The serum is mostly water, of a yellowish color as it dissolves proteins, hormones, minerals and carbon dioxide and is also a very important source of electrolytes. The normal human serum is governed by four isoelectric points: 1-alpha located isoelectric point pH: 5.5 isoelectric point gamma 2- situated pH 9 and pH 12.5 betta 3- Isoelectric point located below pH 4 and 4- delta isoelectric point located above 12.5.In the blood serum they are not simultaneously represented four isoelectric points .The serum isoelectric point is located next .to pH 8

Just simply: serum is very slightly more acidic than plasma. The change may be due to the addition of anticoagulant (you would have to say which one), and/or loss of the coagulant protein buffers. My rough average estimate would be 0.07 more acidic for the serum.

This article shows the effects of adding an anticoagulant on the pH, it makes it more acidic in proportion to the amount of anticoagulant (in this case heparin for an ABG) As this is unclotted, it is called plasma. A lot of heparin can make it quite acidotic, so advised to use a very small amount.

Effect of heparin on arterial blood gases

• March 1985
• Annals of Emergency Medicine 14(3):233-8
• DOI:
• 10.1016/S0196-0644(85)80446-7
• Source
• PubMed
• Project:
• Medical Toxicology: General
• 📷Gary Joseph Ordog
• 📷Jonathan Wasserberger
• S Balasubramaniam