This study investigated the diagnostic performance of point-of-care ultrasound (POCUS) for acute kidney injury (AKI) etiological subgroups in emergency department (ED) patients. Multi-organ POCUS including kidney, bladder, inferior vena cava (IVC), lung and cardiac examinations were used to identify five AKI subgroups: hypovolemia, reduced cardiac output, systemic vasodilatation and renal vasomodulation, renal and post-renal. One hundred sixty-five AKI patients were included in the study. The most diagnostic parameter in the post-renal group was the presence of any hydronephrosis, with a sensitivity of 93.3% (95% confidence interval [CI]: 68.1-99.8) and specificity of 85.9% (95% CI: 79.3-91.1). For the reduced cardiac output group, the most diagnostic parameter was IVC maximum diameter >17 mm with a sensitivity of 100% (95% CI: 83.2-100) and specificity of 70.2% (95% CI: 61.6-77.7). For the hypovolemia group, the most diagnostic parameter was IVC maximum diameter ≤17.9 mm with a sensitivity of 81.2% (95% CI: 71.2-88.8) and specificity of 56.5% (95% CI: 44-68.4). For the systemic vasodilatation and renal vasomodulation group, the most diagnostic parameter was diffuse ascites with a sensitivity of 56.3% (95% CI: 29.9-80.2) and specificity of 89.9% (95% CI: 83.8-94.2). None of the parameters were significant for the renal group. We concluded that multi-organ POCUS is of diagnostic value for AKI subgroups.