AKI can be classified by prerenal, intrarenal and postrenal. Prerenal causes of AKI are factors external to the kidneys. These functions reduce systemic circulation, causing a reduction in renal blood flow and lead to decreased glomerular perfusion and filtration. For example, hypovolemia, decreased cardiac output, decreased peripheral vascular resistance and vascular obstruction decrease the effective circulative blood volume. Other prerenal causes are burns, bilateral renal vein thrombosis, heart failure, etc. Intrarenal causes include conditions that cause direct damage to renal tissue (parenchyma), resulting in impaired nephron function. Some common causes are severe crush injury, malignant hypertension, nephrotoxic injury, hemolytic blood transfusion reaction, etc. Finally, postrenal AKI involve mechanical obstruction of urinary outflow. The most common causes are benign prostatic hyperplasia, prostate cancer, calculi, trauma and extrarenal tumours.