Inclusion Criteria:  Clinical diagnosis of pneumonia (community acquired pneumonia, hospital acquired pneumonia or ventilator associated pneumonia); Voluntarily signed informed consent; ≥18 years old; Platelet count ≤75×109/L  Exclusion Criteria:  A history of hematopoietic stem cell transplantation or solid organ transplantation such as liver, kidney or lung; Hematological malignancy; Immune thrombocytopenia, such as SLE, ITP, TTP, etc. The length of stay in ICU is less than 24h; Pregnant or lactation patients;