Can help diagnose the underlying cause in acute kidney injury
- 10:1–20:1 can be normal or may indicate a postrenal cause.
- ≥ 20:1 indicates prerenal cause: Urea reabsorption is increased, which is typical in patients with dehydration or hypoperfusion.
- Because increased urea reabsorption is mediated by ADH, in order to build medullary concentration gradient. See Renal physiology > Collecting duct
- ≤ 15:1 indicates intrarenal cause: Renal damage causes decreased urea reabsorption.