In an adult with autosomal‑dominant polycystic kidney disease, which urine parameters should be evaluated to detect early renal injury, infection, and other complications?

Urine Testing in Autosomal Dominant Polycystic Kidney Disease

Measure albumin-to-creatinine ratio (ACR) in a laboratory setting rather than using dipstick testing, as albuminuria is typically mild in ADPKD and requires sensitive detection methods. 1

Essential Urine Parameters to Monitor

Albuminuria/Proteinuria Assessment

• Laboratory ACR measurement is mandatory because dipstick testing lacks the sensitivity and specificity needed to detect the mild albuminuria characteristic of ADPKD (median ACR 3.2 mg/mmol in adults, with 49% having moderate albuminuria ≥3 mg/mmol and only 3.4% having severe albuminuria ≥30 mg/mmol). 1
• Proteinuria serves as both a marker of chronic kidney disease progression and a cause of further tubulointerstitial damage and glomerular hypertrophy, making its detection and control critical for renal survival. 1
• Regular monitoring of proteinuria should be considered standard care for all ADPKD patients regardless of age. 1

Urinary Sodium Excretion

• Measure 24-hour urinary sodium as it correlates directly with kidney growth and disease progression. 1
• Higher urinary sodium levels (surrogate for dietary sodium intake) increase the risk of a composite endpoint including 50% reduction in eGFR, end-stage renal disease, or death in later-stage ADPKD. 1
• Target dietary sodium intake should not exceed 2000 mg/day, which may require dietician assistance to achieve. 1, 2

Infection Detection Parameters

For Suspected Urinary Tract Infection

• Obtain both urine and blood cultures before initiating antibiotics in any febrile ADPKD patient, as this distinction is critical for appropriate treatment duration. 1, 3
• Standard urinalysis showing pyuria and positive urine culture confirms uncomplicated UTI, which occurs in 15-25% of children and 21-75% of adults with ADPKD. 1, 3, 4
• Apply standard pediatric or adult UTI diagnostic protocols, as no evidence suggests increased incidence of complicated infections in ADPKD patients. 1, 3, 4

For Suspected Cyst Infection (Distinct from UTI)

• Cyst infections do NOT cause typical UTIs because infected cysts are isolated from the urinary tract and do not communicate with the collecting system. 3
• When fever >38°C occurs with acute flank/abdominal pain and localized tenderness, measure inflammatory markers: C-reactive protein ≥50 mg/L OR white blood cell count >11 × 10⁹/L suggests cyst infection rather than simple UTI. 3
• Blood cultures are essential as bacteremia occurs in approximately 60% of cyst infections. 3
• Urine cultures may be negative in cyst infections since the infection is confined to cyst fluid. 3

Hematuria Evaluation

• Document presence of microscopic or macroscopic hematuria, which occurs in 5-15% of children and 64% of adults with ADPKD. 1, 4, 5
• Gross hematuria before age 30-35 years is associated with worse renal survival in adults, making early identification prognostically important. 1, 4
• Hematuria itself bears no direct relationship to the rate of renal function decline, so its presence should not alter management beyond investigation for other causes. 5

Urine Osmolality

• Assess urine concentrating ability as ADPKD patients have both central (blunted vasopressin release) and nephrogenic defects in osmoregulation even with normal renal function. 6
• Patients with ADPKD are more sensitive to water deprivation and produce higher levels of endogenous vasopressin to reach similar urine osmolality levels compared to healthy individuals. 1, 6
• Dehydration should be avoided; encourage adequate hydration (>2.5 L daily) to satisfy thirst. 1, 2

Common Pitfalls to Avoid

• Never rely on dipstick testing alone for proteinuria assessment in ADPKD, as it will miss the mild but clinically significant albuminuria that requires treatment with ACE inhibitors or ARBs. 1
• Do not assume positive urine culture equals simple UTI in febrile ADPKD patients—always obtain blood cultures and measure inflammatory markers to distinguish cyst infection (requiring 4-6 weeks of lipid-soluble antibiotics) from uncomplicated UTI (requiring ≤7 days of standard therapy). 3
• Avoid treating asymptomatic bacteriuria, as it does not require intervention in ADPKD patients. 3
• Do not perform urinary tract instrumentation unnecessarily, as it precipitates infection in 43% of cases with considerable morbidity and mortality. 5