Lower Serum Chloride at ICU Admission Is Associated With Acute Kidney Injury in Critically Ill Solid Tumour Patients: A Retrospective Cohort Study

Background Acute kidney injury (AKI) is common in cancer intensive care units (ICUs) and is associated with high mortality. Although chloride plays a key role in renal haemodynamics, its clinical significance is often underemphasised. However, the relationship between serum chloride and AKI in oncological critical care remains unexplored in observational studies. Methods We analysed 846 consecutive solid tumour ICU admissions (≥3 days, 2018-2024) without AKI within 48 hours of admission. Hypochloraemia was defined as serum chloride <96 mmol/L. AKI was adjudicated using KDIGO creatinine criteria. Multivariable logistic regression and ROC analyses were performed. Results AKI developed in 416 patients (49.2%). Admission chloride was lower in those who developed AKI (97.0 ± 11.3 vs 104.0 ± 12.5 mmol/L, P < 0.001). After adjustment for illness severity (APACHE II score) and baseline renal function (eGFR), among other confounders, patients with hypochloraemia had 87% higher odds of AKI than those with normochloraemia (OR 1.87, 95% CI 1.14-2.60). Furthermore, each 1 SD decrement (11.5 mmol/L) in serum chloride raised the AKI risk by 46.5% (OR 1.465, 95% CI 1.134-1.792). Discriminative AUCs were 0.751 for any AKI and 0.819 for stage 3 AKI; optimal cut-offs (97 mmol/L and 92 mmol/L, respectively) lay at or below the reference range. Associations remained consistent across baseline estimated glomerular filtration rate strata. Conclusions Lower serum chloride is a readily identifiable and potentially modifiable predictor of AKI in critically ill solid tumour patients. The potential of real-time chloride monitoring and early repletion as low-cost AKI prevention strategies warrants prospective evaluation.