In routine biochemical testing, yellow tubes with blood clot activator and serum separation gel or red tubes with activator but no gel are commonly used. Fibrin formation can be unstable if the activator's amount or concentration is improper, leading to jelly-like serum. Centrifugation time also matters; if blood is centrifuged too soon, red blood cells and platelets detach from the fibrin network, causing jelly-like serum. Physiological and pathological factors, like myocardial infarction or heparin treatment, can also cause jelly-like serum. In such cases, stirring the clot and aspirating the serum without it can help. The jelly-like appearance may result from tube type, collection technique, or sample abnormalities, requiring attention to ensure test accuracy.

Blood is composed of blood cells and plasma. Centrifugation can use the density difference between blood cells and plasma (or serum) to make them layer under the centrifugal force by high-speed rotation. In this way, the upper-layer serum or plasma can be conveniently obtained for various testing items, such as detecting biochemical indicators like blood glucose, blood lipids, liver and kidney functions. Most of these tests require pure serum or plasma to ensure the accuracy of the results.