D3.09 - Cyto-LTT as a Diagnostic Tool in Acute Drug-Induced Interstitial Nephritis: A Case Report and Laboratory Case Series

Acute immuno-allergic interstitial nephropathies (AIN) are rare and their etiology (drug-induced, autoimmune or infections) is often difficult to determine. Detailed drug history is crucial yet identifying the culprit drug remains challenging. Systemic or local eosinophilia (blood, urine, biopsy) may support diagnosis but is inconsistently present, and cutaneous manifestations are frequently absent. We describe a case of cloxacillin-induced AIN supported by cyto-LTT findings, and evaluate the contribution of cyto-LTT in suspected drug-induced AIN through analysis of a laboratory case series.

Clinical history, chemistry, and renal biopsy findings were collected during the acute phase of AIN in an 81-year-old patient. Three years later, an allergy workup included skin tests and cyto-LTT. The ADR-AC laboratory cyto-LTT database was retrospectively analyzed for cases referred for suspected drug-induced nephritis between 2018 and 2024.

The patient was treated in December 2019 for cervical spondylodiscitis with cefotaxime and amoxicillin for 24 hours, followed by cloxacillin. On day 15, acute renal failure occurred (creatinine: 177 μmol/L, urea: 10.9 mmol/L, eosinophilia 0.61G/L) without skin manifestations. Cloxacillin was discontinued after negative infectious work-up. Renal biopsy showed interstitial oedema with diffuse infiltrates, mild eosinophilic infiltration, tubular lesions with numerous lymphocyte exocytosis, and no immunoglobulin deposits. Skin tests were negative at 20 minutes, 24 hours and 72 hours readings, but cyto-LTT showed high IL-5, IL-13, IFNγ and granzyme B secretion in response to cloxacillin, while not to amoxicillin or cefotaxime. Database analysis identified 83 cases with suspected drug-induced nephritis. Cyto-LTT was positive for at least one drug in 26 patients (31.3%), implicating 24 different substances, most frequently beta-lactams;. seven cyto-LTT positive patients did not present any skin manifestations.

This case highlights the diagnostic challenges of immuno-allergic AIN and shows cyto-LTT can identify the culprit drug even years after the acute reaction. Although limited by its retrospective and non-controlled nature, the laboratory case series supports the clinical value of cyto-LTT in suspected drug-inducednephritis, particularly when skin manifestations are absent.