What is the primary purpose of performing a urinalysis in suspected renal disease?

• A. To interpret BUN and creatinine levels via Urine Specific Gravity (USG)
• B. To measure serum creatinine
• C. To interpret hydration status using serum osmolality
• D. To assess liver enzymes

Answer: (C)

The key idea is that a urinalysis helps assess the kidney’s ability to concentrate urine, which reflects hydration status and renal function. By measuring how concentrated the urine is (urine specific gravity, and if available urine osmolality), you learn whether the kidneys are effectively concentrating urine or if there’s an abnormal dilution. Serum osmolality, on the other hand, is a blood test and isn’t obtained from a urinalysis, so using it to judge hydration from a UA isn’t appropriate. In addition to concentrating ability, a urinalysis can reveal other signs of renal disease, such as protein, blood, crystals, casts, and infection markers, all of which provide important clues about renal pathology.