Question

In a patient with AKI, which laboratory urinalysis result indicates tubular damage?

a. Hematuria
b. Specific gravity fixed at 1.010
c. Urine sodium of 12 mEq/L (12 mmol/L)
d. Osmolality of 1000 mOsm/kg (1000 mmol/kg)

Answer 1

A specific gravity fixed at
`1.010` indicates tubular damage in a patient with AKI. This is because normally functioning kidneys can vary urine concentration, whereas tubular damage prevents the kidney from properly concentrating or diluting urine.

Step-by-step explanation:

In a patient with acute kidney injury (AKI), laboratory urinalysis results can indicate the presence of tubular damage. One such indicator is the specific gravity of the urine. Specific gravity fixed at
`1.010` suggests that the tubules are damaged and cannot concentrate or dilute the urine properly. This is contrary to normal circumstances, where specific gravity varies depending on the hydration status of the individual. Normal functioning kidneys can produce urine with a wide range of specific gravity, from about
`1.002` to
`1.035`, suggesting the ability to concentrate or dilute urine as needed.

Other potential indicators of tubular damage on urinalysis could include the presence of cellular casts or elevated levels of certain substances that the healthy kidney would typically reabsorb, but they are not part of the provided options. Hematuria could be indicative of various conditions, including injuries outside of the tubules. A low urine sodium (such as urine sodium of
`12 mEq/L`) can be associated with prerenal causes of AKI, while a high level might suggest tubular damage, but this alone is not sufficient for a diagnosis. Lastly, osmolality of
`12 mEq/L` would typically be observed in a highly concentrated urine and, although it suggests good concentrating ability, it is not a specific indicator of tubular damage without additional context.