A nurse is caring for a client who reports to the clinic for laboratory tests. The client has an acute kidney injury caused by acute tubular necrosis and asks why their glomerular filtration rate (GFR) keeps decreasing. Which of the following pathophysiological changes occurring in the kidney should the nurse explain as the cause of the decrease?

The correct answer is choice C: "You will need to avoid rigorous exercise during the test."

Rationale:

• Choice A: The collection time for a 24-hour urine creatinine clearance test typically starts at a specific time, not necessarily with the first urine of the day.
• Choice B: A creatinine clearance test requires a 24-hour urine collection, not just 12 hours.
• Choice C: Avoiding rigorous exercise is important during the test as it can affect creatinine levels and impact the accuracy of the results.
• Choice D: Storing the urine container in a dark location is not necessary for a creatinine clearance test.

Choice A reason: In acute kidney injury (AKI), the blood urea nitrogen (BUN) level is expected to be elevated due to the kidneys' impaired ability to excrete urea, which is a waste product of protein metabolism. Normal BUN levels range from approximately 7 to 20 mg/dL.

Choice B reason: Hypercalcemia is not commonly associated with AKI. Instead, patients with AKI may experience hypocalcemia due to the kidneys' reduced ability to convert vitamin D to its active form, which is necessary for calcium absorption.

Choice C reason: Metabolic alkalosis is not a typical finding in AKI. More commonly, patients with AKI experience metabolic acidosis because the kidneys are unable to excrete acid effectively, leading to an accumulation of acid in the body.

Choice D reason: Hypokalemia is generally not expected in AKI. The condition is more often associated with hyperkalemia, as the impaired kidney function leads to a reduced excretion of potassium, which can accumulate to dangerous levels.