What is the normal value for urinary albumin-to-creatinine ratio (ACR)?

Normal Urinary Albumin-to-Creatinine Ratio (ACR)

The normal value for urinary albumin-to-creatinine ratio is less than 30 mg/g creatinine (or <3 mg/mmol), which is classified as "normal to mildly increased albuminuria" (category A1) and represents the lowest risk for chronic kidney disease progression and cardiovascular events. 1

Standard Reference Ranges

The current classification system divides ACR into three categories 1:

• A1 (Normal to Mildly Increased): <30 mg/g (<3 mg/mmol)

  • Equivalent to 24-hour albumin excretion rate <30 mg/day 1
  • Equivalent to urine protein-to-creatinine ratio <150 mg/g 1

• A2 (Moderately Increased Albuminuria): 30-299 mg/g (3-29 mg/mmol)

  • Previously termed "microalbuminuria" 1
  • Equivalent to 24-hour albumin excretion 30-299 mg/day 1

• A3 (Severely Increased Albuminuria): ≥300 mg/g (≥30 mg/mmol)

  • Previously termed "macroalbuminuria" 1
  • Equivalent to 24-hour albumin excretion ≥300 mg/day 1

Clinical Significance Within Normal Range

Even within the "normal" range of <30 mg/g, ACR functions as a continuous risk marker, with higher values within this range associated with increased cardiovascular and renal risk. 1

• Values between 10-30 mg/g (high-normal range) carry higher risk than values <10 mg/g 2, 3
• Research suggests ACR cutoff values >8-10 mg/g may predict chronic kidney disease progression in patients with type 2 diabetes, even though this falls within the "normal" range 2
• Community-based studies demonstrate that high-normal UACR (10-30 mg/g) is associated with increased all-cause mortality compared to low-normal values (<10 mg/g) 3

Important Testing Considerations

To confirm abnormal albuminuria, two of three specimens collected within a 3-6 month period should be elevated, due to high biological variability exceeding 20% between measurements. 1

Several factors can falsely elevate ACR independently of kidney damage 1, 4:

• Exercise within 24 hours
• Active infection or fever
• Congestive heart failure
• Marked hyperglycemia
• Menstruation
• Marked hypertension

First morning void urine samples provide the most reliable results with the lowest coefficient of variation (31%) and should be used for ACR measurement. 4

Management for Normal ACR

For patients with ACR <30 mg/g and normal blood pressure 1, 5:

• ACE inhibitors or ARBs are not recommended for primary prevention
• Annual monitoring is appropriate for patients with diabetes or kidney disease risk factors 5
• Focus on optimizing glycemic control and maintaining blood pressure at target levels 5