Baseline systemic inflammatory indices and clinicopathological features to predict the outcome of acute tubulointerstitial nephritis : A single-center retrospective study.

Background: Acute tubulointerstitial nephritis (AIN) is an immune-mediated disorder that can cause acute kidney injury (AKI). We aimed to investigate the characteristics of patients with AIN and predictive factors for treatment response.

Material and methods: In this study, thirty-one patients diagnosed with AIN on kidney biopsy between 2006 and 2021 were included. Baseline clinical, histopathological, and laboratory findings, including complete blood count (CBC), creatinine, erythrocyte sedimentation rate, C‑reactive protein, C3, C4, systemic immune inflammation index (SII), neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and urinalysis were evaluated. Treatment response, mortality, and creatinine levels at the time of last follow-up were also noted.

Results: The median age was 46 years and 80.6% were female. Median baseline creatinine and proteinuria levels were 4.1 mg/dL and 0.84 gram/day. The median follow-up period was 14 months and 93.5% received immunosuppressives. End-stage kidney disease (ESKD) developed in five patients (16.1%). Renal recovery (creatinine < 1.4 mg/dL) was observed in 17 patients (54.8%). Higher degrees of interstitial fibrosis, tubular atrophy, granuloma formation, global glomerulosclerosis, and higher baseline hemoglobin levels, in addition to a longer interval between first symptom to initiation of immunosuppressives were associated with renal nonrecovery, statistically. Also, patients who progressed to ESKD had higher baseline hemoglobin (p = 0.033) and lymphocyte (p = 0.044) and lower PLR levels (p = 0.016), as well as higher degrees of global glomerulosclerosis (p = 0.014), interstitial fibrosis (p = 0.042), and tubular atrophy (p = 0.030).

Conclusion: Treatment response rates are low for AIN, which may lead to ESKD. Besides chronicity in histopathology specimens, higher baseline hemoglobin levels and lower platelet-to-lymphocyte ratio might be prognostic. Further studies should be conducted on new markers for AIN.