Urine findings that support glomerulonephritis in AKI include which of the following?

• A. Eosinophils in urine
• B. FeNa <15% or urine Na <10 with RBC casts and proteinuria
• C. Muddy brown casts
• D. FeNa >2% with bland urine

Answer: (B)

In AKI attributable to glomerular disease, the urine often shows red blood cell (RBC) casts and proteinuria because the glomerular basement membrane is damaged and leaks protein while blood cells escape into the filtrate and form casts in the tubules. The fractional excretion of sodium (FeNa) helps separate prerenal azotemia from intrinsic renal injury, but in glomerulonephritis the tubules can still reabsorb sodium well, so FeNa may remain relatively low (less than about 15%). Therefore, a finding of RBC casts and proteinuria with a FeNa under 15% supports glomerulonephritis as the cause of AKI.

By contrast, eosinophils in urine point toward acute interstitial nephritis; muddy brown casts point to acute tubular necrosis; and a high FeNa with bland urine is typical of ATN rather than GN.