What is a UACR (Urine Albumin-to-Creatinine Ratio) test?

What is a UACR Urine Test?

The UACR (Urine Albumin-to-Creatinine Ratio) test is a screening tool that measures the amount of albumin (a protein) relative to creatinine in a random spot urine sample to detect kidney damage, particularly in patients with diabetes, hypertension, or cardiovascular disease. 1

How the Test Works

The UACR test normalizes albumin excretion for variations in urine concentration by measuring both albumin and creatinine simultaneously in a single urine sample. 2 This approach eliminates the need for burdensome 24-hour urine collections while providing accurate results. 1

• The test is performed on a random spot urine sample, ideally a first morning void, which has the lowest coefficient of variation (31%) compared to other collection methods. 2
• Measuring albumin alone without creatinine is less expensive but susceptible to false-negative and false-positive results due to variations in urine concentration from hydration status. 1
• The UACR correlates well with timed excretion measurements and is the best method to predict kidney-related events in people with type 2 diabetes. 2

Interpreting UACR Results

Normal UACR is defined as <30 mg/g creatinine, while values ≥30 mg/g indicate increased urinary albumin excretion. 1, 2

The results are categorized as follows:

• Normal to mildly increased: <30 mg/g 1, 2
• Moderately increased albuminuria (formerly "microalbuminuria"): 30-299 mg/g 1, 2
• Severely increased albuminuria (formerly "macroalbuminuria"): ≥300 mg/g 1, 2

UACR is a continuous measurement, meaning that differences within both normal and abnormal ranges are associated with kidney and cardiovascular outcomes. 1, 2 Even values within the "normal" range carry prognostic significance for future risk.

Clinical Applications

The UACR test is primarily used to screen for and monitor chronic kidney disease (CKD), particularly diabetic kidney disease, which occurs in 20-40% of patients with diabetes. 1

Screening Recommendations:

• Type 1 diabetes: Begin screening 5 years after diagnosis 2
• Type 2 diabetes: Begin screening at the time of diagnosis 2
• Annual screening is recommended for adults with diabetes using morning spot urine samples 2

Monitoring Frequency:

• If eGFR is <60 mL/min/1.73 m² and/or albuminuria is ≥30 mg/g, repeat UACR every 6 months to assess disease progression. 2
• For patients with moderately increased albuminuria (30-299 mg/g), monitor UACR and eGFR at least annually. 2

Important Clinical Caveats

Due to high biological variability in urinary albumin excretion (>20%), two of three abnormal specimens collected within a 3-6 month period should be confirmed before diagnosing albuminuria. 1, 2, 3

Factors That Can Falsely Elevate UACR:

• Exercise within 24 hours 2, 3
• Infection or fever 2, 3
• Congestive heart failure 2, 3
• Marked hyperglycemia 2, 3
• Menstruation 2, 3
• Marked hypertension 2, 3

These transient elevations can lead to false-positive results, which is why confirmation testing is essential. 2, 3

Advantages Over Alternative Methods

UACR demonstrates stronger associations with kidney failure compared to urine protein-to-creatinine ratio (UPCR), particularly in patients with higher levels of albuminuria. 4 In a meta-analysis of 148,994 participants, UACR showed an adjusted hazard ratio of 2.55 per standard deviation increment for kidney failure, compared to 2.40 for UPCR (P<0.001). 4

• Timed or 24-hour urine collections are more burdensome and add little to prediction or accuracy compared to spot UACR testing. 1, 2
• Point-of-care UACR strip tests are available with sensitivities ranging from 80-96% and specificities of 84-94%, making them useful for screening in primary care settings. 5, 6, 7