Direct comparison
Serum vs Plasma: Clot, Anticoagulant, Tube Types
Serum vs plasma: clotted blood without anticoagulant vs anticoagulated blood, with the tube types, handling steps and sources for each.
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How do Serum, Plasma compare side by side?
The table below compares Serum, Plasma across 10 procurement-relevant dimensions, from how the sample is obtained through source.
Side-by-side comparison
| Dimension | Serum | Plasma |
|---|---|---|
| How the sample is obtained | From clotted blood that has not been mixed with an anticoagulant; the clot is removed by centrifugation (Labcorp; Vignoli et al. 2022). | From blood mixed with an anticoagulant in the collection tube; the liquid is separated from the cells by centrifugation (Labcorp; StatPearls). |
| Fibrinogen and clotting factors | Fibrinogen is removed, and most clotting factors are consumed during clot formation (Labcorp; StatPearls). | Plasma retains fibrinogen, the clotting component, and contains clotting factors; anticoagulants block their activity in the tube (Labcorp; StatPearls). |
| Tube additive | Red-top: no anticoagulant or preservative. Gel-barrier tubes (mottled red/gray, gold, cherry red-top): clot activator and separator gel, but no anticoagulant (Labcorp). | Green-top: sodium or lithium heparin. Lavender-top: K2 EDTA. Blue-top: sodium citrate, used only as 3.2% citrate tubes (Labcorp). |
| Before centrifugation | Labcorp says to let the blood clot at room temperature for 30 to 60 minutes first. Spinning before clotting is complete lets a fibrin clot form on top of the cells. | No clotting wait: Labcorp says to centrifuge immediately, for as long as 10 minutes or as the tube manufacturer specifies. |
| After centrifugation | Labcorp: separate serum from cells within 45 minutes to two hours, depending on the test. Do not spin more than 10 minutes unless otherwise specified. | Handled as the tube manufacturer and the test requirements specify (Labcorp). |
| What the fluid is made of | The fluid remaining after blood coagulation; it resembles plasma but lacks fibrinogen and most clotting factors (StatPearls). | About 90-92% water, with proteins (albumin, globulins, fibrinogen), electrolytes, nutrients, hormones, dissolved gases and waste products; about 55% of total blood volume (StatPearls). |
| Gel-barrier caveat | Labcorp: do not use gel-barrier tubes for therapeutic drug monitoring, and check the test description to see whether a gel-barrier tube is acceptable. | Not applicable to the anticoagulant tubes listed above; the test description still decides which tube is acceptable (Labcorp). |
| Are the two interchangeable? | No. In a 1H NMR metabolomics comparison, serum showed higher lactate and lower pyruvate than both EDTA and citrate plasma (Vignoli et al. 2022). | No. Citrate plasma showed lower GlycA/GlycB and generally lower lipoproteins than EDTA plasma and serum; tube gel, clot activator and additives can add their own signals (Vignoli et al. 2022). |
| When to pick each | Pick serum when the test description calls for a serum specimen, using the clot-activator, gel-barrier or plain red-top tube it specifies. | Pick plasma when the test description calls for a plasma specimen, using the heparin, EDTA or citrate tube it names. Do not mix tube types within one study (Vignoli et al. 2022). |
| Source | Labcorp, Blood Specimens: Chemistry and Hematology (labcorp.com/test-menu/resources/blood-specimens-chemistry-and-hematology), read 2026-10-30. | StatPearls, Physiology, Blood Plasma (NBK531504, PubMed 30285399) and Vignoli et al., J Proteome Res 2022;21(4):1061-1072, doi:10.1021/acs.jproteome.1c00935, read 2026-10-30. |
Common questions
Common questions about Serum vs Plasma
What is serum sample type?
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Serum is the fluid left after blood has clotted and the clot has been removed by centrifugation. It comes from blood collected without an anticoagulant, in a plain red-top tube or a clot-activator gel-barrier tube (Labcorp). It lacks fibrinogen and most clotting factors (StatPearls).
What is found in plasma but not in serum?
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Fibrinogen. Labcorp states that the essential difference is that plasma retains fibrinogen, which is removed from serum. Most clotting factors are likewise consumed when blood clots, so they are largely absent from serum (StatPearls).
Does plasma contain clotting factors?
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Yes. Plasma contains fibrinogen and clotting factors such as factor VIII and factor IX. In a collection tube, anticoagulants (heparin, EDTA or citrate) interfere with the activity of those factors so the sample does not clot (Labcorp).
What is plasma made of?
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About 90-92% water, plus proteins (albumin, globulins, fibrinogen), electrolytes, nutrients, hormones, dissolved gases and metabolic waste products. It makes up about 55% of total blood volume (StatPearls, Physiology, Blood Plasma, 2026).
Which collection tubes give serum and which give plasma?
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Per Labcorp: red-top and gel-barrier tubes (mottled red/gray, gold, cherry red-top) have no anticoagulant and give serum. Green-top (sodium or lithium heparin), lavender-top (K2 EDTA) and blue-top (sodium citrate) tubes contain anticoagulants and give plasma. Follow the test description for the tube it requires.
Going deeper
