Which finding is characteristic of intrarenal (intrinsic) renal disease?

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Intrinsic renal disease damages the renal tubules so they can’t reabsorb properly, leading to tubular epithelial debris that forms casts in the urine. The most characteristic finding is granular (muddy brown) casts in the urine sediment, which reflect tubular injury such as acute tubular necrosis. This pattern is more specific for intrarenal pathology than other urine or blood test changes.

Elevated urine sodium (a high value) happens because damaged tubules lose their reabsorptive ability, but it isn’t as specific as the sediment finding. A low BUN to creatinine ratio (around 10:1) fits intrinsic injury because urea reabsorption is impaired, but again it’s less definitive than seeing the granular casts. Low specific gravity indicates an impaired ability to concentrate urine and can occur in intrinsic AKI, but it’s not as diagnostic as the presence of granular casts.