Some phlebotomists may wonder why there are both SST™ tubes and PST™ tubes that are used for chemistry tests. It may be unclear as to why phlebotomists cannot use them interchangeably. While these tubes are used for many of the same tests, they do have their own unique qualities.
The PST™ tube is used for STAT general chemistry orders and the SST™ tube is used for more routine chemistry blood tests.
The blood sample in an SST™ tube has to clot before the serum can be used. This usually takes about 30 minutes.
The PST™ tube offers a whole blood specimen that can be used almost immediately, which is why it is used for STAT orders.
What is the Difference Between the Chemicals in the PST™ and SST™ Vacutainer® Blood Collection Tubes?
The Plasma Separator Tube, also referred to as PST™, contains lithium heparin and plasma separator gel; whereas, the Serum Separator Tube, also referred to as SST™, contains a clot activator and a serum separator gel.
The SST™ Tube
There are two kinds of SST™ tubes. One tube has a Gold stopper and the other has a Red-Gray Marble stopper. These tubes have a clot activator on the glass and a polymer gel as the separator. These tubes are used to separate the blood cells from the serum. The tube must be inverted five times following blood collection. This mixes the blood with the clot activator that lines the inside of the tube. The clot activator ensures that clotting occurs within 30 minutes after collection.
The PST™ Tube
There is only one kind of PST™ tube. It has a mint green stopper. This tube is only used on patients who are in the hospital. This tube contains lithium heparin to keep the blood from clotting and has a gel plasma separator. This tube is used to obtain whole blood, plasma. To ensure that the blood does not clot, the tube must be inverted eight times following blood collection. This tube is used for therapeutic drug monitoring and general chemistries. Because the PST™ tube contains lithium, it cannot be used to test a patient’s lithium level.