Serum-separating tube

SSTs are sometimes called "gold-topped tubes", "tiger-tops", or "marble-top tubes", referring to the stoppers which are either gold, red with a gold ring on top, or marbled red and grey.

Trademarked versions of the SST include Covidien "Corvac" tubes.

[3]  This is used in the tubes so the blood adheres to the surface of the tiny silica particles and begins to clot.

The gel in SST II tubes (which appears slightly less opaque) is supposed [weasel words] to have less effect on drug levels in serum.

[citation needed] Blood samples should be allowed time to form a clot at room temperature for 30–60 min.