What is serum separation tubes with gold/yellow top?

Serum separation tubes, also known as gel clot activator tubes or SST blood collection tubes, are used in medical clinical chemistry tests requiring blood serum.

SST tubes are sometimes called "yellow-top tubes", or "gold-top tubes", referring to the stoppers which are either yellow or gold. The SST blood tube contain particles to hasten blood clotting as well as a special gel that separates blood cells from serum. The clear serum can then be extracted from the blood sample and used for testing by centrifuging it.

The drug or hormone may diffuse from the serum into the gel and produce a drop in the recorded level, hence serum separator tubes should be handled carefully when determining drug or hormone levels. It is thought that the gel in SST tubes, which has a somewhat less opaque appearance, has less of an impact on the serum drug levels.

What is the substance called inside a serum separation tube?

Spray-coated silica and a polymer gel are both included in SST blood collection tubes to separate serum. People use STT tubes for serum analyses in chemistry, serology, immunology, and HIV assays. The gel at the serum separation tube's bottom known as the serum separator serves as a durable chemical and physical barrier between the serum and the blood clot.

What is the gel and what does the gel do in the serum separating tube?

Separation gel is frequently used in various blood collection tubes, following centrifugation, it creates a temporary barrier between blood cells and the serum/plasma layer. If the transfer of the serum or plasma is delayed or the blood collection tube is unintentionally pushed over after centrifuging, this helps avoid the layers from becoming mixed up again. The gel barrier also makes it possible to pour off the serum/plasma layer rather than pipet it. In rare circumstances, tests can be run directly from the primary tube without the requirement for transfer. Another advantage is that the gel helps to stop or delay glycolysis as well as other negative consequences that could happen if the serum or plasma is in touch with the red blood cells for an extended period of time.

Although blood clotting can be accelerated without the use of a separator gel in procoagulant blood collection tubes, clots and serum can be separated by prolonged contact. Furthermore, blood cells are fragile and can easily hemolise and interfere with the serum sample, which can be solved by using a separator gel to separate the compartments.

The serum/plasma layer should, whenever possible, be transferred a few hours after centrifugation because the separation gel does not provide benefits for permanent separation. The majority of routine clinical chemistry studies are unaffected by the separation gel, although some drug/hormone assays may be negatively impacted.

How to centrifuge the serum separator tube( Yellow/Gold-top tube)?

When using a serum separator tube, collect the specimen using the standard venipuncture technique. Gently invert the tube five times to mix the clot activator with the blood. Avoid vigorous agitation of collected specimens. Allow the tube to clot for 20-30 minutes in a vertical position. Do not centrifuge immediately after drawing the blood. Do not allow the blood to clot with the tube in a horizontal position. Do not allow the SST tubes to stand more than one hour before centrifuging.

Centrifuge the tube for 10-15 minutes at about 1300-1800 xg. The centrifuge RPMs will differ depending on the centrifuge and rotor used. The gel barrier will develop, keeping the serum and clot apart. The gel must remain intact and the cells and serum must be thoroughly separated after centrifugation. If the barrier is not complete, do not centrifuge the tube again.

Reference:

https://en.m.wikipedia.org/wiki/Serum-separating_tube

https://teacherscollegesj.org/what-is-the-gel-in-sst-tube/

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