VetSkill PCA Lab and Diagnostics Practice Test

Serum is obtained by letting blood clot and then removing the solid clot and cells; so you need a tube that does not prevent clotting. A plain red-top tube has no additive, which lets the blood clot naturally and, after centrifugation, yields the clear liquid serum. Tubes containing EDTA or heparin contain anticoagulants, which stop clotting and produce plasma instead of serum. A tube with a clot activator speeds up clotting but still ends up producing serum; however, for standard serum collection the plain red-top tube is the typical choice because it contains no additives to interfere with the clotting process.