How often should the urine Albumin to Creatinine Ratio (ACR) test be repeated?

When to Repeat Urine Albumin-to-Creatinine Ratio (ACR)

For patients with normal ACR (<30 mg/g), repeat testing annually; for those with elevated ACR (≥30 mg/g) or eGFR <60 mL/min/1.73 m², repeat every 6 months. 1

Initial Confirmation of Abnormal Results

When you first detect an elevated ACR, the high day-to-day biological variability demands confirmation before making clinical decisions:

• Confirm any initial elevated ACR with 2 additional tests over the subsequent 3-6 months before diagnosing persistent albuminuria 2, 3
• Use first morning void samples for all confirmatory testing to minimize variability (coefficient of variation 31% vs higher with random samples) 1, 3
• Avoid testing during urinary tract infections, menstruation, marked hyperglycemia, fever, or within 24 hours of exercise, as these cause false elevations 3

Important caveat: While guidelines traditionally recommend confirming with multiple tests, recent evidence in type 2 diabetes shows that a single abnormal ACR (2-20 mg/mmol or approximately 18-177 mg/g) has a 96.8% positive predictive value for persistent albuminuria 4. However, given the treatment implications and guideline recommendations, confirmation remains the standard of care 1, 2.

Routine Monitoring Frequency by Risk Category

For Patients with Normal ACR (<30 mg/g)

• Test annually in all patients with diabetes (starting 5 years after type 1 diabetes diagnosis or at type 2 diabetes diagnosis) 1
• Test annually in patients with hypertension 1
• Consider biennial testing (every 2 years) for low-risk type 1 diabetes patients with ACR ≤10 mg/24 h (approximately ≤14 mg/g) AND HbA1c ≤8% 5

For Patients with Moderately Elevated ACR (30-299 mg/g)

• Test every 6-12 months to monitor progression 1
• Test every 6 months if concurrent eGFR <60 mL/min/1.73 m² 1
• Consider 6-month intervals for high-risk patients (ACR 21-30 mg/24 h or HbA1c ≥9%) 5

For Patients with Severely Elevated ACR (≥300 mg/g)

• Test every 6 months (twice yearly) 1, 2
• Test every 6 months if eGFR <45 mL/min/1.73 m² regardless of ACR level 2

When to Increase Monitoring Frequency

Beyond the baseline schedule, increase testing frequency when:

• Starting or adjusting ACE inhibitors, ARBs, or SGLT2 inhibitors to assess treatment response 2
• Clinical status changes (new cardiovascular events, acute kidney injury, worsening glycemic control) 2
• eGFR declining even with normal ACR 6
• Poor blood pressure or glycemic control in patients with diabetes or hypertension 6

Risk-Stratified Monitoring Algorithm

The KDIGO guidelines provide a color-coded grid for monitoring frequency based on both GFR category and albuminuria category 1:

• Green zone (eGFR ≥60 + ACR <30): Monitor annually
• Yellow zone (eGFR 45-59 or ACR 30-299): Monitor 1-2 times per year
• Orange zone (eGFR 30-44 or ACR ≥300): Monitor 2-3 times per year
• Red zone (eGFR <30): Monitor 3-4 times per year and ensure nephrology referral 1

Critical Pitfalls to Avoid

Don't over-interpret small changes: Due to substantial day-to-day variability, only large changes indicate true progression. For patients with microalbuminuria (ACR 30-300 mg/g), a change of ±170% is needed to represent significant change with 95% certainty 7. For macroalbuminuria (ACR >300 mg/g), ±83% change is required 7.

Don't rely on a single test for major decisions: The biological variability means that 25% or more change in eGFR category should be confirmed before declaring progression 1.

Don't forget to test ACR at all: While eGFR testing rates exceed 89% in diabetes patients, ACR testing rates are only 52-73%, leading to missed CKD diagnoses 8. The prevalence of detected elevated albuminuria increases linearly with testing frequency 8.

Referral Timing

• Consider nephrology referral when eGFR <45 mL/min/1.73 m² or ACR consistently >300 mg/g 2
• Immediate nephrology referral when eGFR <30 mL/min/1.73 m² 2
• Consider referral for uncertainty about kidney disease etiology or difficult management issues 1