Reference Range for Albumin-Creatinine Ratio
The normal albumin-to-creatinine ratio (ACR) is ≤30 mg/g creatinine, with values >30 mg/g indicating abnormal albuminuria that warrants further evaluation. 1
Standard Reference Ranges
The albumin-creatinine ratio should be reported and interpreted using the following thresholds 1:
- Normal to mildly increased (A1): <30 mg/g creatinine (<3 mg/mmol)
- Moderately increased albuminuria (A2): 30-299 mg/g creatinine (3-29 mg/mmol) - formerly called "microalbuminuria"
- Severely increased albuminuria (A3): ≥300 mg/g creatinine (≥30 mg/mmol) - formerly called "macroalbuminuria"
Measurement Methodology
Use spot urine albumin-to-creatinine ratio rather than timed collections, as this method is more convenient, eliminates collection errors, and correlates well with 24-hour measurements. 1
- First morning void is preferred for children and adolescents to avoid orthostatic proteinuria, though random specimens are acceptable for adults. 1
- Laboratories should report results as milligrams of albumin per gram of creatinine (mg/g). 1
- Alternative units include mg/mmol (multiply mg/g by 0.113) or mg/mg (divide mg/g by 1000). 2
Confirmation Requirements
A single elevated value should not be considered diagnostic - persistent albuminuria must be confirmed before making treatment decisions. 1
- Confirm values >30 mg/g with 2 of 3 positive samples collected over 3-6 months, particularly in patients with diabetes. 1
- Patients should avoid vigorous exercise for 24 hours before collection, as physical activity causes transient elevation. 1, 2
- Exclude transient causes including urinary tract infection, menstrual contamination, marked hyperglycemia, uncontrolled hypertension, and heart failure before confirming persistent albuminuria. 2
Important Caveats
While the traditional cutoff of 30 mg/g defines "normal," emerging evidence suggests that higher values within the normal range may still carry prognostic significance. Research demonstrates that ACR values >10 mg/g in diabetic patients predict CKD progression, and values in the upper normal range (>5-10 mg/g) are associated with increased cardiovascular risk. 3, 4 However, the established clinical threshold of 30 mg/g remains the standard for defining abnormal albuminuria and triggering intervention. 1
For patients with very high proteinuria (spot urine protein-to-creatinine ratio 500-1,000 mg/g or higher), measurement of total protein instead of albumin is acceptable, with a normal range <200 mg/g. 1
Screening Recommendations
- Annual screening is recommended for all adults with diabetes, hypertension, or family history of chronic kidney disease. 1
- Testing should begin at diagnosis for type 2 diabetes, but can be delayed until 5 years after diagnosis for type 1 diabetes (unless poor control or family history warrant earlier testing). 1
- If ACR is >30 mg/g or eGFR <60 mL/min/1.73 m², repeat testing every 6 months to assess progression and treatment response. 1