Are there any contraindications for measuring the urine albumin-to-creatinine ratio (UACR)?

Contraindications for Urine Albumin-to-Creatinine Ratio Testing

There are no specific contraindications for measuring the urine albumin-to-creatinine ratio (UACR). However, there are several factors that can affect the accuracy of results and should be considered when interpreting UACR values.

Factors Affecting UACR Measurement Accuracy

• Exercise within 24 hours, infection, fever, congestive heart failure, marked hyperglycemia, menstruation, and marked hypertension may elevate UACR independently of kidney damage, potentially leading to false-positive results 1
• High biological variability of urinary albumin excretion necessitates confirmation of elevated values with 2-3 specimens collected over a 3-6 month period before diagnosing albuminuria 1
• First morning void urine samples are preferred for measurement to minimize variability 1, 2
• Collections should be at the same time of day, and the person should not have ingested food for at least 2 hours prior to collection to further minimize variability 2

When to Perform UACR Testing

• For type 1 diabetes: Begin screening 5 years after diagnosis 1
• For type 2 diabetes: Begin screening at the time of diagnosis due to difficulty in precisely dating disease onset 1
• Annual screening is recommended for adults with diabetes using morning spot urine samples 1
• If eGFR is <60 mL/min/1.73 m² and/or albuminuria is >30 mg/g creatinine, UACR should be repeated every 6 months to assess changes 1

Interpretation of Results

• Normal UACR is defined as <30 mg/g creatinine 1
• Moderately increased albuminuria (formerly microalbuminuria): 30-299 mg/g creatinine 1
• Severely increased albuminuria: ≥300 mg/g creatinine 1
• Some studies suggest sex-specific cutoff values for ACR (>17 mg/g in men or >25 mg/g in women) due to differences in creatinine excretion 2

Clinical Pearls

• UACR is a continuous measurement, and differences within both normal and abnormal ranges are associated with renal and cardiovascular outcomes 1
• Spot urine samples for albumin-to-creatinine ratio are preferred over timed or 24-hour collections, which are more burdensome and add little to prediction or accuracy 1
• Measurement of spot urine for albumin alone without simultaneously measuring creatinine is less expensive but susceptible to false-negative and false-positive results due to variations in urine concentration 1
• The high day-to-day variability of UACR (coefficient of variation of approximately 49%) means that a repeated measurement could be as low as 0.26 times or as high as 3.78 times the first measurement 3
• Multiple urine collections may improve the capacity to monitor changes over time but may not be necessary for the initial diagnosis of albuminuria 3

Limitations of Point-of-Care Testing

• Point-of-care UACR tests show lower sensitivity (83.2%) compared to laboratory-based measurements, making them better for ruling out albuminuria (negative predictive value 95.0%) than ruling it in (positive predictive value 51.2%) 4
• When using point-of-care testing, consider confirmation with laboratory testing for positive results 4