Inflammation is the body's defense response to irritation, manifested as redness, swelling, heat, pain, and dysfunction, and includes both infectious and non-infectious inflammation.

Any factor that can cause tissue damage can be a reason of inflammation, which can be broadly divided into the following categories: Biological factors (bacteria, viruses, Rickettsiae, mycoplasma, fungi, spirochete and parasites, etc.), physical factors (high temperature, low temperature, radioactive substances, ultraviolet light and mechanical damage, etc.), chemical factors (strong acids, alkalis, turpentine, mustard gas, etc.). Decomposition products of necrotic tissue, metabolites accumulated in the body under pathological conditions such as urea, etc.), foreign bodies (various metals, wood debris, dust particles and surgical sutures, etc.), necrotic tissue, allergic reactions.

Interleukin-6 (IL-6), procalcitonin (PCT), and C-reactive protein (CRP) are all included in the Expert Consensus on the Interpretation of Clinical Significance of Infection-related Biomarkers, which can be used to distinguish infection from non-infection.

The Expert Consensus on the Clinical Use of Serum amyloid A in Infectious Diseases proposed that when the serum level of amyloid protease A (SAA) is less than 10mg/L, the risk of infection is not high; serum levels of SAA ≥10mg/L indicate an increased risk of infection events.