What are the normal urine albumin‑to‑creatinine ratio (UACR) values and the cut‑offs for micro‑ and macro‑albuminuria?

Normal UACR Values and Albuminuria Classification

Normal UACR is ≤30 mg albumin/g creatinine, microalbuminuria is 30-300 mg/g, and macroalbuminuria is >300 mg/g. 1

Standard Reference Ranges

• Normal (A1 category): UACR <30 mg/g creatinine 1, 2
• Microalbuminuria (A2 category - Moderately Increased): UACR 30-300 mg/g creatinine 1, 2
• Macroalbuminuria (A3 category - Severely Increased): UACR >300 mg/g creatinine 1, 2

Measurement Methodology

Use spot urine albumin-to-creatinine ratio rather than timed collections, as 24-hour urine collections are burdensome and add little to prediction accuracy. 1

• First-morning spot urine samples are preferred to minimize variability, particularly in children and adolescents to avoid orthostatic proteinuria effects 1
• Laboratories should report results as milligrams of albumin per gram of creatinine 1
• UACR is a continuous measurement where differences within normal and abnormal ranges correlate with renal and cardiovascular outcomes 1

Confirmation Requirements

Persistent albuminuria requires confirmation with 2 out of 3 elevated samples (>30 mg/g) collected over 3-6 months before initiating treatment. 1, 3, 2

Pre-collection Precautions:

• Patients should avoid vigorous exercise for 24 hours before sample collection 1
• False elevations can occur with hematuria, febrile illness, or recent vigorous exercise 2
• Single ACR measurements have 40-50% variability, making confirmation essential 2

Clinical Context for High-Normal Values

**Even UACR values within the "normal" range (<30 mg/g) carry prognostic significance.** Research demonstrates that UACR >8-10 mg/g in diabetic patients predicts CKD progression risk, though this is not yet incorporated into formal guideline definitions. 4

• In hypertensive non-diabetic patients, approximately 20% have high-normal UACR (20-30 mg/g), which is associated with increased cardiovascular risk 5
• UACR correlates with systolic/diastolic blood pressure, pulse pressure, and age as independent risk factors 5

Common Pitfalls

• Avoid measuring albumin alone without creatinine, as this is susceptible to false results due to hydration-related urine concentration variations 1
• Do not use 24-hour timed collections for routine screening, as spot UACR provides equivalent clinical information with better patient compliance 1
• Refrigerate samples for same-day or next-day assay; one freeze is acceptable if necessary, but avoid repeated freeze-thaw cycles 1