Processing omics samples may be new for many lab technologists. So it important that you know, understand and follow the protocol. Plasma is the straw coloured liquid portion of the blood that remains after cellular components are removed. It contains mainly water, salts, enzymes, antibodies and proteins. The buffy coat is the thin layer between the straw coloured plasma and the fluid containing the red cells that becomes visible after spinning. The buffy coat contains most of the white blood cells and the platelets.
PST tubes contain a special gel to aid separation and this prevents the buffy coat from forming. However, if using an EDTA tube for plasma preparation, take care not to include any cells from this layer when aliquoting the plasma. Serum is the liquid fraction of whole blood that is collected after the blood has been allowed to clot. The clot is removed by centrifugation and the supernatant fluid, the serum, is carefully removed with a Pasteur pipette.
Using your GMC’s standard operating procedure for preparing plasma and serum, select the correct blood tubes from your rack. That’s the green PST tubes for plasma or the gold SST tube for serum or another approved container. Place the tube in the centrifuge in a sealed bucket to prevent aerosols from being formed. Delaying spinning could lead to haemolysis, resulting in the presence of haemoglobin in the supernatant. For this reason, plasma should be prepared within six hours of the blood being taken.
Make sure your centrifuge is properly balanced and leave the brake off. Spin the blood at 1,300 to 2,000 G for up to 15 minutes, depending on which type of rota you are using. Allow the centrifuge to come to rest naturally and then carefully remove the tubes and place them in your rack. Then, using a clean Pasteur pipette carefully decant aliquots of supernatant into barcoded FluidX tubes and freeze immediately at -80° Celsius. For cancer referrals, you will also be required to collect 10 millilitres of blood in EDTA or Streck tubes for circulating tumour DNA. This needs to be spun and separated in a specialised manner, so please refer to the latest NHS England protocols.
RNA, or ribonucleic acid, is a single-stranded molecule, whose many functions in the body include the transcribing of genetic code from DNA in order to make proteins. Your package of samples should hold a PAXgene blood RNA collection tube containing a sample of blood from the patient. PAXgene tubes enable blood to be stabilised for long periods of time so that high-quality RNA can be extracted in the future. After aliquoting, store at -80° Celsius immediately.