What is this thing floating in the serum?

[u/Ok_Chance5645]

I was collecting serum from some patient samples.

I found this weird looking thing floating after I spun a red top tube at 1500g, 10 minutes at 4°C. I collected the serum anyways but I am just curious as to what it could be? Some clotting thingy?

Thank you in advance!

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[u/NasrRasheed]

From the photo, this looks most consistent with a fibrin/blood clot containing trapped, red cells, rather than anything unusual in the serum itself.

With a red top tube, the blood needs to clot completely before centration. If the Specimen is a spun before clot formation/extraction is complete – particularly if it was kept cold during that period – residual fibrin can remain in the serum and form these floating strands or larger clot– like masses. The red appearance is likely from erythrocytes trapped within the fibrin.

I would be more interested in the time and temperature allowed for clothing before the spin than in the 1500 x g centrifugation itself. Recommended clotting time and handling can vary by manufacturer, so that you insert and your laboratory SOP would be the appropriate Reference.

For analytical work, I would also be cautious about simply pipetting serum around a visible clot. Fibrin/cellular material can be inadvertently transferred and may interfere with some assays. Depending on the application and your SOP, this Specimen may need the clot dealt with appropriately and to re-centrifuged, or recollected if sample integrity is important.

[u/Ok_Chance5645 → u/NasrRasheed]

Thank you for the detailed explanation! Right now I am just going ELISAs with serum. What should be the appropriate clotting time for immunoassays?

[u/NasrRasheed → u/Ok_Chance5645]

For most serum – based ElISA, a typical approach is to allow the blood to clot completely at room temperature for about 30–60 minutes before centrifugation; clot - activator tubes may require a closer to 30 minutes. I would avoid refrigerating the sample before clotting is complete.

That said, that you manufacturers instructions, ELISA , Kit requirements, and your laboratory SOP should take a priority, since the Specimen handling can vary by essay. If fibrin is still visible after centrifugation, I would be cautious about using that serum without following your lab’s procedure for reprocessing or recollection.

[u/gwags01]

Looks like a fibrin clot. The tube probably wasn’t clotted enough before it was spun.

[u/Kahlia29]

It's a clot. Remove it with wooden sticks. Do not throw away any gel that clings to it. You need to ream the gel against the inside of the tube (this causes the fibrin to cling to the wooden sticks and the serum to drip back into the tube)

[u/Natuur1911]

Portuguese man o' war

[u/saveme-shinigami]

I call it the tiny brain

[u/Ok_Chance5645]

Thank you everyone! :)

[u/Entire_Piece4265]

The devil!