4600 MPO AND PR3 DUAL POSITIVE ANCA AND ANA: A CASE REPORT

Abstract Background and Aims Anti-neutrophil cytoplasmic antibody (ANCA) vasculitis has been thought to be a relatively rare disease, although it has been increasing in incidence recently likely due to improved testing and recognition. One of two main antigens are targeted in this condition, either proteinase 3 (PR3) or myeloperoxidase (MPO). Uncommonly, both antigens can be targeted in specific situations such as during levisamole use, propylthiouracil use, hydralazine use or infections. Herein, we illustrate a case of a patient who presented with progressively worsening kidney function in the setting of recent COVID booster. Method A 79 year old female with a history of hypertension, hyperlipidemia, acid reflux and hypothyroidism was admitted to our facility from her outpatient nephrologist due to abnormal labs. This was the first time the patient had seen a nephrologist, although she was told that her serum creatinine (SCr) was elevated to ∼3 mg/dL three months earlier. At that time, she noted blood tinged urine as well as frothiness of urine that had since resolved. She also endorsed a raised erythematous rash that also resolved. She did mention that she had increasing fatigue over the past week prior to presentation along with weight loss over the past few months. She denied ear pain, sinus pain, epistaxis, hemoptysis or specific joint pain. She denied any kidney stones or NSAID use. She was a former smoker, having quit decades ago. She denied any current tobacco or illicit drug use, including cocaine as well as any herbal supplements or medications that were not otherwise prescribed to her by a medical provider. She did note recent COVID booster prior to being told of a SCr ∼3 mg/dL. She had a repeat kidney function test one month prior to presentation, at which time she was told her SCr was 5 mg/dL. In our Emergency Department, SCr was elevated to 8.45 mg/dL with a BUN of 68 mg/dL. Computed tomography of the abdomen and pelvis ruled out any hydronephrosis or kidney stones. Urinalysis was revealing for 509 RBCs, 39 WBCs, WBC casts as well as granular casts. Spot urine protein to creatinine ratio was found to be elevated at 6925 mg/g. Serologies were pertinent for a positive ANA as well as ANCA. Interestingly, both MPO and PR3 titres were elevated at 72 AU/mL and 391 AU/mL, respectively. Kidney biopsy was performed and revealed a pauci-immune glomerulonephritis with crescents along with mixed interstitial inflammatory infiltrate (Figure 1). The diagno