When to Order Albumin-to-Creatinine Ratio (ACR) Testing
The ACR test should be ordered annually in all adults with type 2 diabetes regardless of treatment duration, and in those with type 1 diabetes with duration of ≥5 years, using a morning spot urine sample. 1
Primary Indications for ACR Testing
Diabetes Screening
- Type 1 Diabetes: Begin screening 5 years after diagnosis 1
- Type 2 Diabetes: Begin screening at diagnosis 1
- Frequency: Annual screening for all diabetic patients with normal results 1
- More Frequent Testing: Every 6 months if:
- eGFR <60 mL/min/1.73 m²
- Previous ACR >30 mg/g creatinine
- Hypertension present 1
High-Risk Populations
- Patients with hypertension
- Family history of kidney disease
- History of cardiovascular disease
- Obesity
- Smoking history 2
Confirming Abnormal Results
- An elevated ACR should be confirmed with 2 additional tests over the next 3-6 months 1
- First-void morning urine samples are preferred for confirmation testing to reduce variability 1
- Rule out transient causes of elevated ACR before confirming diagnosis:
- Exercise
- Urinary tract infection
- Marked hyperglycemia
- Marked hypertension
- Congestive heart failure
- Pyuria
- Hematuria 2
Interpreting ACR Results
Classification of Albuminuria
| Category | ACR Range (mg/g creatinine) |
|---|---|
| Normal to mildly increased | <30 |
| Moderately increased (microalbuminuria) | 30-299 |
| Severely increased (macroalbuminuria) | ≥300 |
| [1] |
Clinical Significance
- ACR ≥30 mg/g indicates increased risk for CKD progression and cardiovascular events 2
- ACR is superior to urine dipstick testing for detecting albuminuria:
Monitoring Response to Treatment
- After initiating treatment (ACE inhibitors/ARBs), monitor ACR every 3-6 months 2
- A >30% sustained reduction in albuminuria is considered a surrogate marker of slowed kidney disease progression 1
- Goal: Reduce ACR by at least 30-50% and ideally achieve ACR <30 mg/g 1
Practical Considerations
- Sample Collection: First-void morning urine sample is preferred; random spot urine is acceptable when first-void is not practical 4
- Point-of-Care Testing: While convenient, has lower sensitivity (83.2%) and positive predictive value (51.2%) compared to laboratory testing 5
- Correlation with Total Protein: ACR correlates well with protein-to-creatinine ratio (PCR), but correlation is weaker in patients with low protein excretion or low urinary creatinine concentration 6
When to Refer to Nephrology
- Uncertain etiology of kidney disease
- Presence of hematuria with albuminuria
- eGFR <60 mL/min/1.73m² with ACR >30 mg/g
- Rapidly progressing kidney disease
- Urgent referral if eGFR <30 mL/min/1.73m² 2
Common Pitfalls to Avoid
- Relying solely on dipstick testing: Dipstick tests have poor sensitivity for detecting microalbuminuria compared to ACR 3
- Not confirming abnormal results: Single elevated ACR may be transient; confirm with 2 additional tests 1
- Ignoring urinary creatinine levels: Low urinary creatinine (<60 mg/dL) may affect the reliability of ACR results 6
- Not considering transient causes: Exercise, infection, and acute hyperglycemia can temporarily increase albumin excretion 2
ACR testing is a critical component of kidney disease screening and management, particularly in diabetic patients, and should be incorporated into routine care to identify early kidney damage and guide treatment decisions.