Serum-separating tube

Serum-separating tubes, also known as serum separator tubes or SSTs, are used in medical clinical chemistry tests requiring blood serum.

A large SST II vacutainer.

SSTs are sometimes called "marble-top tubes" or "yellow topped tubes", referring to the stoppers which are either gold or red-gray. Trademarked versions include Covidien "Corvac" tubes.

They contain a special gel that separates blood cells from serum, as well as particles to cause blood to clot quickly. The blood sample may then be centrifuged, allowing the clear serum to be removed for testing.

These tubes should be used with care when measuring therapeutic endocrine levels because the drug/hormone may diffuse from the serum into the gel, causing a reduction in measured drug level. The gel in SST II tubes (which appears slightly less opaque) is supposed to have less effect on drug levels in serum.

Further reading

SST Tubes are NOT known as Yellow Tops. Gold Top is acceptable, however SST is the only correct terminology. Yellow Tops are VERY different and the use of the term "Yellow Top" with an inexperienced Phlebotomist or Nurse could result in the sample being rejected by the lab for incorrect tube/sample as there are yellow top tubes which contain different additives from the SST. In addition, taking the order of draw into consideration, a yellow top tube used in confusion of terminology where an SST was required, when more than one kind of tube is being drawn, can and will result in sample cross contamination, making most, if not all tubes rejectable in the lab.

• Vacutainer
• Venipuncture