Certified Nephrology Nurse Certification (CNN) Practice Exam 2025 – Comprehensive All-in-One Study Guide for Exam Success!

The correct answer highlights the inability to concentrate urine, which leads to polyuria and salt wasting. This is characteristic of medullary cystic kidney disease, a disorder that affects the kidneys' ability to concentrate urine due to cyst formation in the renal medulla. The resulting polyuria means that patients may produce a larger volume of dilute urine, losing significant amounts of electrolytes, particularly sodium.

In this condition, the kidneys' structural changes impede their normal concentrating ability, leading to symptoms associated with fluid and electrolyte imbalances. The consequence of this also includes a compensatory increase in fluid intake, which may arise from dehydration symptoms.

On the other hand, the other choices reflect conditions not typically associated with medullary cystic kidney disease. Oliguria with fluid retention generally points to an acute or chronic injury state rather than the cystic condition. Hematuria after exercise indicates possible trauma or nephron strain rather than a structural kidney disease like the one described. Lastly, proteinuria with nephrotic syndrome suggests glomerular aetiologies, which are distinct from the tubular dysfunction seen in medullary cystic kidney disease.

Overall, the focus on urine concentration issues makes the selected answer the most relevant indicator of this specific renal condition.