What does Albumin-to-Creatinine Ratio (ACR) measure?

From the Guidelines

ACR, or albumin-to-creatinine ratio, measures the amount of albumin (a protein) in urine relative to creatinine, and is primarily used to detect and monitor kidney damage, especially in conditions like diabetes and hypertension. The test specifically identifies microalbuminuria, which is an early sign of kidney disease before symptoms appear. A normal ACR is less than 30 mg/g, while values between 30-300 mg/g indicate microalbuminuria, and over 300 mg/g suggests macroalbuminuria (significant kidney damage) 1.

Key Points

• ACR is preferred over a simple urine albumin test because it accounts for urine concentration variations 1.
• The test requires only a single urine sample, making it convenient for routine monitoring.
• Regular ACR testing is recommended for diabetic patients and those with hypertension to catch kidney disease early when treatment is most effective 1.
• Factors such as exercise, infection, fever, congestive heart failure, marked hyperglycemia, menstruation, and marked hypertension may elevate ACR independently of kidney damage 1.
• ACR is a continuous measurement, and differences within the normal and abnormal ranges are associated with renal and cardiovascular outcomes 1.

Interpretation of ACR Results

• ACR < 30 mg/g: normal
• ACR 30-300 mg/g: microalbuminuria
• ACR > 300 mg/g: macroalbuminuria (significant kidney damage) 1

Clinical Recommendations

• Use urine ACR as the initial test for albuminuria, with a first void in the morning midstream sample preferred in adults and children 1.
• Confirm reagent strip positive albuminuria and/or proteinuria by quantitative laboratory measurement and express as a ratio to urine creatinine wherever possible 1.

From the Research

What ACR Measures

• The Albumin to Creatinine Ratio (ACR) is a measure used to assess kidney function and detect kidney damage 2, 3, 4.
• ACR measures the amount of albumin (a protein) in the urine compared to the amount of creatinine (a waste product) 2, 3, 4.
• It is used as a screening test for microalbuminuria, which is a sign of early kidney damage 4.
• ACR is also used to monitor protein excretion in patients with chronic kidney disease (CKD) 2.

Factors Affecting ACR

• Urine creatinine concentration can affect the ACR measurement, with lower concentrations leading to higher ACR values 3.
• Age and sex can also affect ACR values, with older adults and women tend to have higher ACR values 4.
• Muscle mass and body weight can also influence ACR measurements, with lower muscle mass and body weight leading to lower urine creatinine concentrations and higher ACR values 3.

Clinical Significance of ACR

• ACR is associated with an increased risk of cardiovascular disease (CVD) events, particularly in individuals with low body weight 3.
• ACR is also used to monitor the progression of kidney disease and the effectiveness of treatments such as angiotensin-converting enzyme inhibitors (ACEi) and angiotensin receptor blockers (ARB) 5, 6.