Final answer:
The NCCLS recommends separating serum or plasma from cells within 30 to 60 minutes of specimen collection. During this time, in the collection tube, clotting occurs to obtain serum, or if plasma is needed, centrifugation separates it from the cells.
Step-by-step explanation:
The NCCLS (National Committee for Clinical Laboratory Standards) recommends that serum or plasma should be separated from the cells within 30 to 60 minutes after blood specimen collection. Within the glass tube, blood must first clot to obtain serum, which typically takes about 30 minutes. The clot is formed by the coagulation process, where the plasma protein fibrinogen is converted into fibrin to trap blood cells. Serum, which is plasma without the coagulation factors, is left as the clear liquid after the cells are trapped in the clot or centrifuged to the bottom of the tube. When plasma is needed, an anticoagulant like EDTA or heparin is used to prevent clotting. The blood is then centrifuged, and the plasma is separated from the blood cells.