At AAV diagnosis, AIP was found to be positively correlated with ESR (r = 0.171, P = 0.028), CRP (r = 0.169, P = 0.030), and blood urea nitrogen (r = 0.187, P = 0.016) and negatively correlated with total serum protein and serum albumin (r = − 0.201, P = 0.010 and r = − 0.209, P = 0.007). Here, CRP is linked to anti-neutrophil cytoplasmic antibody-associated vasculitis.