Does a patient with a single kidney (unilateral kidney) experience polyuria or nocturia (nocturnal polyuria)?

Relationship Between Single Kidney and Polyuria/Nocturnal Polyuria

Patients with a single kidney are more likely to experience nocturnal polyuria due to altered renal salt and water handling mechanisms, though this is not universal for all patients with a unilateral kidney.

Pathophysiology of Polyuria in Single Kidney Patients

• Reduced renal function in patients with a single kidney can impair salt and water homeostasis, which may drive nocturnal or 24-hour polyuria 1
• The compensatory mechanisms in a single kidney can lead to altered natriuresis (sodium excretion), which is a primary driver of nocturnal polyuria rather than inability to concentrate urine 2
• As renal function deteriorates, nocturnal polyuria becomes more prominent due to osmotic diuresis mainly caused by increased nighttime sodium excretion 2

Diagnostic Considerations

• A frequency volume chart (FVC) for 3 days is essential to diagnose polyuria or nocturnal polyuria in patients with a single kidney 3
• 24-hour polyuria is defined as greater than 3L urine output in 24 hours 3
• Nocturnal polyuria is diagnosed when more than 33% of the 24-hour urine output occurs at night 3
• Patients with chronic kidney disease (CKD) or a single kidney should have the following assessed:
  • Thirst and fluid intake patterns 1
  • Medication review (diuretics, lithium, calcium channel blockers, NSAIDs) 1
  • Blood pressure and presence of edema 1
  • Urinalysis for hematuria and albumin/creatinine ratio 1
  • Blood tests (urea, creatinine, electrolytes, eGFR) 1

Clinical Implications

• Single kidney patients may experience increased nocturnal voiding frequency due to increased nocturnal urine output 4
• This can lead to sleep disturbance and daytime fatigue 4
• As renal function deteriorates in patients with a single kidney, there is a significant negative relationship between creatinine clearance and night/day ratio of urine volume 2

Management Approaches

• Treatment should focus on addressing the underlying mechanisms of nocturnal polyuria in single kidney patients:

  • Optimize blood pressure control 1
  • Dietary adjustment to reduce salt intake 1, 2
  • Regulation of fluid intake, especially in the evening 3, 1
  • Review and adjust timing of medications, particularly diuretics 3

• For persistent bothersome symptoms:

  • Antidiuretic treatment may be warranted for patients with nocturnal polyuria 5
  • Desmopressin (a synthetic analog of arginine vasopressin) can reduce nocturnal urine output in patients with nocturnal polyuria syndrome 4

Important Caveats

• Not all patients with a single kidney will develop polyuria or nocturnal polyuria - it depends on the compensatory function of the remaining kidney 2
• A link between single kidney status and nocturia should not be assumed without confirmation via frequency volume charts and appropriate testing 3
• Treatment of nocturnal polyuria in single kidney patients should prioritize addressing modifiable factors before considering pharmacological interventions 3, 1
• Careful monitoring of renal function is essential when using medications like desmopressin in patients with a single kidney 4