Understanding Albumin-to-Creatinine Ratio (ACR) of 30-300 mg/g
An albumin-to-creatinine ratio (ACR) of 30-300 mg/g creatinine indicates moderately increased albuminuria, also known as microalbuminuria, which represents an early marker of kidney damage and increased risk for cardiovascular disease and kidney disease progression. 1, 2
Classification and Clinical Significance
- ACR values are categorized by KDIGO guidelines into three levels: A1 (normal to mildly increased, <30 mg/g), A2 (moderately increased, 30-300 mg/g), and A3 (severely increased, >300 mg/g) 1, 2
- Moderately increased albuminuria (30-300 mg/g) represents an intermediate risk category for kidney disease progression and cardiovascular outcomes 2
- Microalbuminuria is an established risk factor for renal disease progression in type 1 diabetes and the earliest clinical sign of diabetic nephropathy 3
- It also signifies abnormal vascular permeability and is associated with higher risk for cardiovascular events in both diabetic and non-diabetic patients 3
Diagnostic Considerations
- Confirmation of elevated ACR requires repeat testing, with at least 2 of 3 specimens collected within a 3-6 month period showing abnormal results to establish persistent albuminuria 2
- Morning spot urine samples are preferred for ACR measurement to minimize variability 2
- Single ACR measurements can have up to 40-50% variability, making confirmation with repeat testing essential 2
- False elevations in ACR can occur with hematuria, febrile illness, or vigorous exercise within 24 hours of collection 2
Clinical Implications and Management
- Normotensive people with diabetes and microalbuminuria (ACR 30-300 mg/g) may be considered for treatment with an ACE inhibitor or ARB 1
- For patients with microalbuminuria, treatment with ACE inhibitors or ARBs can reduce albuminuria and slow CKD progression 1, 4
- The presence of microalbuminuria should trigger intensified modification of common risk factors for renal and cardiovascular disease: hyperglycemia, hypertension, dyslipidemia, and smoking 4
- Blood pressure targets should be maintained at <130/80 mmHg in patients with diabetes or kidney disease 3
- In diabetic patients, maintaining HbA1c <7% helps prevent progression of albuminuria 4
Measurement Considerations
- The albumin-to-creatinine ratio in a spot urine sample is the preferred screening method for albuminuria assessment 3
- When using ACR in early morning void instead of 24-hour urinary albumin excretion (UAE), about 88% of patients are classified in corresponding albuminuria categories 5
- Muscular mass can affect ACR interpretation, as urinary creatinine reflects muscle mass - patients with low muscle mass may have falsely elevated ACR values without true microalbuminuria 6
Monitoring Recommendations
- Annual ACR screening is recommended for patients with diabetes 7
- For patients with type 1 diabetes, screening should begin after 5 years of disease duration, while for type 2 diabetes, screening should start at diagnosis 7
- ACR should be checked every 6 months within the first year of treatment to assess the impact of antihypertensive therapy 3
Understanding the clinical significance of an ACR of 30-300 mg/g is crucial for early intervention to prevent progression to overt nephropathy and reduce cardiovascular risk.