SAA is similar to CRP and is used to evaluate the acute reaction process. SAA is a sensitive parameter. It begins to increase after about 8 hours of inflammatory reaction, and the time to exceed the upper limit of the reference range is earlier than that of CRP. However, the difference between the median value of CRP in normal people and the upper limit of the reference range is about 10 times. In SAA, it is only 5 times. For mild infections, for example, many viral infections, elevated SAA is more common than CRP. In infectious diseases, the absolute increase of SAA is higher than that of CRP, so the determination of SAA, especially for "normal" and minor acute reactions, should provide better differentiation. SAA is usually elevated in patients with a cold about 2pm 3, but CRP is also elevated in patients with less than 1pm 2. In viral infection cases, elevated concentrations of SAA and CRP were found in patients with adenovirus infection. The response patterns of SAA and CRP are parallel in the recovery phase of acute infection, which is suitable for both bacterial and viral infections. SAA was not elevated in lupus erythematosus and ulcerative colitis. The increase of SAA in the stage of malignant tumor metastasis is usually higher than that in the organ stage of the tumor. SAA detection is a very sensitive index for transplant rejection. In a study of kidney transplant recipients, 97% of the tests for rejection were based on elevated SAA. In the detection of irreversible transplant rejection, the average concentration was 690 ±29mg/L, while the correlation level in patients with reversible rejection was 271 ±31mg/L. A chronic increase in SAA concentration in patients with rheumatoid arthritis, tuberculosis or leprosy is a prerequisite for the synthesis of AA- starch fibers, which is also used to diagnose secondary amyloidosis.