Brewing Trouble: Tea Consumption and AKI in a Patient on Immune Checkpoint InhibitorTherapy

Introduction: Acute interstitial nephritis (AIN) is a well-recognized immune related adverse effect (irAE) of immune checkpoint inhibitors (ICIs). AIN can also be secondary to other drugs such as proton pump inhibitors (PPIs), and less commonly, hyperoxaluria – which may result from malabsorption or excessive dietary intake of oxalate-rich foods. Thus, AIN poses a diagnostic challenge in patients with multiple risk factors, often necessitating a kidney biopsy to identify the underlying cause. Case Description: A 70-year-old female with chronic kidney disease, gastric bypass, and lung adenocarcinoma on immunotherapy was evaluated for acute kidney injury (AKI). The patient had recently started ICI and PPI therapies and had an increase in serum creatinine from a baseline of 1.7 mg/dL to 2.9 mg/dL seven days post-initiation of ICI therapy. Urinalysis was negative for hematuria and proteinuria. ICI-induced nephritis was considered unlikely due to the timing of AKI onset and absence of other irAEs. The patient reported substantial tea consumption preceding the AKI. A kidney biopsy revealed AIN with scattered tubulointerstitial calcium oxalate crystal deposition (Fig 1). Discontinuation of her tea and initiation of a prolonged steroid taper led to a return of renal function to baseline. Discussion: This case highlights the diagnostic challenge of AKI in the context of multiple potential AIN culprits, including ICI therapy in CKD, PPI use, and dietary consumption of tea in gastric bypass patients. AKI in patients on ICI therapy warrants a broad differential diagnosis, including a full assessment of irAEs, past medical and surgical history and dietary habits. This case highlights the value of kidney biopsy in distinguishing between potential etiologies and guiding appropriate management without interrupting lifesaving cancer treatment.Figure 1: Kidney biopsy. (A) Medullary tubulointerstitial inflammation with eosinophils (arrows). Scatted medullary (B) and cortical (C) calcium oxalate crystals under polarized light.