Acute Dialysis Quality Initiative (ADQI) group, aid in assessment of the severity of a person's acute kidney injury. The acronym RIFLE is used to define the spectrum of progressive kidney injury seen in AKI: Risk: 1.5-fold increase in the serum creatinine, or glomerular filtration rate (GFR) decrease by 25 percent, or urine output <0.5 mL/kg per hour for six hours. Injury: Two-fold increase in the serum creatinine, or GFR decrease by 50 percent, or urine output <0.5 mL/kg per hour for 12 hours. Failure: Three-fold increase in the serum creatinine, or GFR decrease by 75 percent, or urine output of <0.3 mL/kg per hour for 24 hours, or no urine output (anuria) for 12 hours. Loss: Complete loss of kidney function (e.g., need for renal replacement therapy) for more than four weeks. End-stage kidney disease: Complete loss of kidney function (e.g., need for renal replacement therapy) for more than three months. Evaluation The deterioration of kidney function may be signaled by a measurable decrease in urine output. Often, it is diagnosed on the basis of blood tests for substances normally eliminated by the kidney: urea and creatinine. Additionally, the ratio of BUN to creatinine is used to evaluate kidney injury. Both tests have their disadvantages. For instance, it takes about 24 hours for the creatinine level to rise, even if both kidneys have ceased to function. A number of alternative markers have been proposed (such as NGAL, KIM-1, IL18 and cystatin C), but none of them are established enough as of 2018 to replace creatinine as a marker of kidney function. Once the diagnosis of AKI is made, further testing is often required to determine the underlying cause. It is useful to perform a bladder scan or a post void residual to rule out urinary retention. In post void residual, a catheter is inserted into the urinary tract immediately after urinating to measure fluid still in the bladder. 50–100 mL suggests neurogenic bladder dysfunction. These may include urine sediment analysis, renal ultrasound and/or kidney biopsy. Indications for kidney biopsy in the setting of AKI include the following: Unexplained AKI, in a patient with two non-obstructed normal sized kidneys. AKI in the presence of the nephritic syndrome. Systemic disease associated with AKI. Kidney transplant dysfunction. In medical imaging, the acute changes in the kidney are often examined with renal ultrasonography as the first-line modality, where CT scan and magnetic resonance imaging