Value of serum amyloid A plus procalcitonin in differential diagnosis of ANCA-associated vasculitis pulmonary involvement and pulmonary bacterial infection

Objective To evaluate the value of serum amyloid A protein (SAA) plus procalcitonin (PCT) in the differential diagnosis of ANCA-associated vasculitis (AAV) pulmonary involvement and pulmonary bacterial infection.Methods From January 2016 to January 2021,AAV patients with pulmonary injury were recruited and divided into two groups of pulmonary involvement and pulmonary bacterial infection.Clinical characteristics,imaging features and laboratory parameters were retrospectively analyzed.Values of the above parameters in differential diagnosis of pulmonary involvement and pulmonary infection were evaluated by receiver operating characteristic (ROC) curve.Results A total of 82 AAV patients complicated with pulmonary lesions were included.There were 43 females and 39 males with a median age of 64(18-86) years.Age and Birmingham Disease Activity Score (BVAS) of pulmonary infection group were higher than those of uninfected group (P>0.05).Serum levels of procalcitonin (PCT),C-reactive protein (CRP),SAA,white blood cell (WBC) and neutrophil (Neu) were significantly higher in pulmonary bacterial infection group than those in non-pulmonary infection group (P<0.05).The area under the ROC curve (AUC=0.899) of PCT plus SAA for differential diagnosis of pulmonary infection was higher than that of PCT,CRP,SAA,WBC and Neu in AAV patients.The optimal cut-off values of serum PCT/SAA for differentiating pulmonary bacterial infection from AAV active pulmonary injury were 0.61 ng/mL and 142.6 mg/l respectively.Conclusion The serum level of PCT/SAA is significantly higher in AAV patients with pulmonary bacterial infection group than those with pulmonary involvement.SAA may be employed as a new parameter for distinguishing AAV patients with pulmonary involvement and pulmonary infection.PCT plus SAA can improve the value of differential diagnosis of AAV pulmonary involvement and pulmonary bacterial infection.