What is the Urine Albumin-to-Creatinine Ratio (UACR)?

What is UACR (Urine Albumin-to-Creatinine Ratio)?

UACR is a laboratory test that measures the ratio of albumin (a protein) to creatinine in a random spot urine sample, expressed as mg of albumin per gram of creatinine (mg/g), and serves as the preferred screening method for detecting kidney damage in patients with diabetes and other at-risk populations. 1

Why Creatinine is Used in the Ratio

• Creatinine normalizes albumin excretion for variations in urine concentration, eliminating the need for inconvenient 24-hour urine collections that are more burdensome and add little to prediction accuracy. 1, 2
• The ratio provides an accurate estimate of albumin excretion rate without requiring timed collections, making it practical for routine clinical use. 2
• Measuring albumin alone without simultaneously measuring creatinine is susceptible to false-negative and false-positive results due to variations in urine concentration from hydration status. 1, 2

Normal Values and Categories

The current classification system (adopted from KDIGO guidelines) divides UACR into three categories: 1

• A1 (Normal to Mildly Increased): <30 mg/g (<3 mg/mmol)
• A2 (Moderately Increased): 30-299 mg/g (3-29 mg/mmol)
• A3 (Severely Increased): ≥300 mg/g (≥30 mg/mmol)

UACR is a continuous measurement, and differences within both normal and abnormal ranges are associated with renal and cardiovascular outcomes. 1 Even values consistently above 30 mg/g within the "normal" range carry increased cardiovascular event risk. 1

Clinical Significance

• At any level of kidney function (eGFR), increased UACR is associated with higher risk for adverse outcomes including CKD progression, cardiovascular events, and mortality. 1, 2
• UACR is the best method to predict renal events in people with type 2 diabetes. 2
• The test identifies diabetic kidney disease, which occurs in 20-40% of patients with diabetes. 1

How the Test is Performed

• Use a random spot urine collection, preferably first morning void, which has the lowest coefficient of variation (31%) compared to other collection methods. 1, 2
• Collections should ideally be at the same time of day, with no food ingestion for at least 2 hours prior to minimize variability. 2
• The test requires simultaneous measurement of both albumin and creatinine from the same urine sample. 1

Factors That Can Falsely Elevate UACR

Several conditions may elevate UACR independently of kidney damage: 2, 3

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

Confirmation Requirements

Due to high biological variability in urinary albumin excretion, two of three specimens collected within a 3-6 month period should be abnormal before diagnosing persistent albuminuria. 1, 2 Recent research confirms this high variability, showing a repeated UACR can be as high as 3.78 times or as low as 0.26 times the first measurement. 4

When to Screen

• Type 1 diabetes: Begin screening 5 years after diagnosis (albuminuria rarely occurs before this or before puberty). 1, 2
• Type 2 diabetes: Begin screening at the time of diagnosis due to difficulty precisely dating disease onset. 1, 2
• Annual screening is recommended for all adults with diabetes using morning spot urine samples. 2, 3

Monitoring Frequency After Diagnosis

• Normal UACR (<30 mg/g): Repeat annually. 3
• Elevated UACR (≥30 mg/g) or eGFR <60 mL/min/1.73 m²: Repeat every 6 months. 2, 3
• Confirmed albuminuria on treatment: Recheck within 6 months after starting treatment to assess response, then annually if successful. 5

Treatment Implications

• For patients with UACR 30-299 mg/g (moderately increased albuminuria): ACE inhibitors or ARBs are recommended, with target blood pressure <130/80 mmHg. 1, 5
• For patients with UACR ≥300 mg/g (severely increased albuminuria): ACE inhibitors or ARBs are strongly recommended. 1

When to Refer to Nephrology

Consider nephrology referral for: 1, 5, 3

• eGFR <30 mL/min/1.73 m² (immediate referral required)
• eGFR <45 mL/min/1.73 m² or ACR consistently >300 mg/g
• Rapidly increasing albuminuria or rapid decline in kidney function
• Presence of blood or white blood cells in urine
• Uncertainty about the cause of kidney disease