Normal Urine Albumin-to-Creatinine Ratio (ACR)
The normal urine ACR is less than 30 mg/g creatinine, with the reference value in healthy young adults being approximately 10 mg/g. 1
Standard Reference Values
ACR <30 mg/g is classified as normal (Category A1) according to KDIGO guidelines, representing the lowest risk for chronic kidney disease progression and cardiovascular events 1, 2
The baseline reference value in healthy young adult men and women is approximately 10 mg/g, meaning an ACR of 30 mg/g represents more than 3 times the normal value 1
Some sources suggest even more refined thresholds within the "normal" range: ACR <10 mg/g is considered truly normal, while ACR 10-29 mg/g is considered "high normal" 1
Clinical Categories Beyond Normal
The KDIGO classification system divides ACR into three main categories 1, 2:
- A1 (Normal to Mildly Increased): <30 mg/g creatinine
- A2 (Moderately Increased Albuminuria): 30-300 mg/g creatinine
- A3 (Severely Increased Albuminuria): >300 mg/g creatinine
Important Clinical Considerations
ACR Functions as a Continuous Risk Marker
Even within the "normal" range of <30 mg/g, higher values are associated with increased cardiovascular and renal risk 2
Research demonstrates that ACR values >10 mg/g in patients with type 2 diabetes can predict CKD progression, suggesting the lower threshold may be clinically relevant 3
Confirmation Requirements
Due to high biological variability (exceeding 20% between measurements), two of three specimens collected within a 3-6 month period should be elevated to confirm abnormal albuminuria 2
Day-to-day variability is substantial: for patients with normoalbuminuria (ACR <27 mg/g), a change greater than ±467% is required to indicate a significant change with 95% certainty 4
Optimal Specimen Collection
First morning void urine samples provide the most reliable results with the lowest coefficient of variation (31%) 2, 5
Collections should ideally be at the same time of day, with no food ingestion for at least 2 hours prior 5
Factors That Can Falsely Elevate ACR
The following conditions may elevate ACR independently of kidney damage 2, 5:
- Exercise within 24 hours
- Active infection or fever
- Congestive heart failure
- Marked hyperglycemia
- Menstruation
- Marked hypertension
Special Population Considerations
Some studies suggest sex-specific cutoff values may be more appropriate: >17 mg/g in men or >25 mg/g in women, due to differences in creatinine excretion 5
In individuals with obesity, the standard 30 mg/g threshold may have decreased performance due to biases related to urinary creatinine excretion, potentially leading to underdiagnosis of albuminuria 6