CRP and hemophagocytic syndrome: When a patient with HLH has a fever or suspected infection, in addition to routine blood analysis, biochemical indicators such as C-reactive protein (CRP) and calcitoninogen (PCT) to assess the patient’s inflammatory status, tests such as pathogenic culture and antigen detection are performed on samples of the patient’s blood, urine, stool, anal swabs, sputum, bronchoscopic lavage, and other possible sources of infection to look for pathogens.