How do I evaluate urine microalbumin results?

Evaluating Urine Microalbumin Results

Microalbuminuria is defined as urinary albumin excretion of 30-299 mg/g creatinine on a random spot urine sample, and diagnosis requires confirmation with 2 out of 3 abnormal specimens collected within a 3-6 month period due to significant day-to-day variability in urinary albumin excretion. 1, 2

Definitions and Reference Ranges

• Normal albumin excretion is ≤30 mg albumin/g creatinine 3
• Microalbuminuria is defined as >30 to 300 mg albumin/g creatinine 3, 1
• Macroalbuminuria (overt proteinuria) is >300 mg albumin/g creatinine 3

Proper Collection and Testing Protocol

• Confirm microalbuminuria with 2 out of 3 abnormal specimens collected within a 3-6 month period 1, 4
• Patients should refrain from vigorous exercise for 24 hours before sample collection 3, 4
• First morning void samples are preferred to minimize effects of orthostatic proteinuria 1, 4
• Refrigerate urine samples for assay the same or next day; one freeze is acceptable if necessary 3
• Standard dipstick tests are inadequate for microalbuminuria detection; specific assays for microalbumin are required 1
• Always adjust for creatinine to account for variations in urine concentration 1

Factors That Can Cause Transient Microalbuminuria

• Exercise within 24 hours of urine collection 1, 4
• Acute infections and fever 1, 4
• Marked hyperglycemia, even without established diabetic nephropathy 1, 2
• Marked hypertension 1, 4
• Urinary tract infections, hematuria, and menstruation 1, 4
• Congestive heart failure 1

Clinical Significance

• Microalbuminuria is an early marker of diabetic nephropathy and predicts progression to overt proteinuria 2, 5
• It serves as an independent marker of increased cardiovascular risk and mortality 1, 5
• Indicates possible underlying vascular dysfunction and endothelial damage 1, 5
• In patients with type 1 diabetes, GFR is stable at low-level microalbuminuria but decreases at 1-4 mL/min/year as albumin excretion increases 2

Follow-up and Management

• For confirmed persistent microalbuminuria, treatment with an ACE inhibitor or ARB should be initiated even if blood pressure is normal 2, 4
• Monitor microalbumin excretion every 3-6 months to assess response to therapy 4
• A reduction in albuminuria of ≥30% is considered a positive response to therapy 4
• Measure serum creatinine at least annually to estimate GFR and stage CKD if present 4
• Monitor serum creatinine and potassium levels when using ACE inhibitors or ARBs 2, 4

Screening Recommendations

• Populations at increased risk for CKD (diabetes, hypertension, family history of CKD) should be screened for microalbuminuria at least annually 3, 1
• Individuals with documented persistent microalbuminuria who are undergoing treatment should be retested within 6 months to determine if treatment goals and reduction in microalbuminuria have been achieved 3

Common Pitfalls to Avoid

• Relying on a single measurement can be misleading; confirmation requires multiple samples 1, 4
• Using standard dipstick tests instead of specific microalbumin assays 1
• Not adjusting for creatinine, which can lead to errors from variations in urine concentration 1
• Failing to account for sex differences in creatinine excretion (consider multiplying concentration in men by 0.68) 3, 1
• Not ruling out transient causes of microalbuminuria before confirming diagnosis 1, 4