What is microalbuminuria?

What is Microalbuminuria

Microalbuminuria is defined as urinary albumin excretion of 30-299 mg/24 hours, 30-299 mg/g creatinine on a spot urine sample, or 20-199 μg/min on a timed collection. 1

Diagnostic Criteria and Measurement

• Diagnosis requires 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
• The preferred screening method is the urine albumin-to-creatinine ratio (UACR) on a spot morning urine sample, which adjusts for variations in urine concentration 1, 3
• Standard urine dipstick tests are inadequate for detection, as they only become positive when protein excretion exceeds 300-500 mg/day 3
• First morning void samples are preferred to minimize effects of orthostatic proteinuria 2

Clinical Significance

Microalbuminuria represents far more than just early kidney damage—it is a marker of generalized vascular dysfunction and endothelial damage throughout the body. 4, 5

In Diabetic Patients

• Microalbuminuria is the earliest clinical sign of diabetic nephropathy, appearing before overt kidney disease develops 1, 6
• In type 1 diabetes, 80% of patients with sustained microalbuminuria will progress to overt nephropathy (≥300 mg/24h) over 10-15 years without intervention 1
• In type 2 diabetes, 20-40% of patients with microalbuminuria develop renal failure without specific interventions 1

Cardiovascular Risk Marker

• Microalbuminuria predicts 2-4 fold increases in cardiovascular events and all-cause mortality, independent of other risk factors 4, 7
• It is present in 5-19% of the general population, up to 23% of hypertensive patients, and up to 40% of diabetic patients 7
• The finding indicates the need for aggressive screening for vascular disease and intervention to reduce all cardiovascular risk factors 1

Pathophysiology

• Microalbuminuria reflects abnormal vascular permeability and the presence of atherosclerosis 3
• It correlates strongly with elevated C-reactive protein levels and abnormal vascular responsiveness to vasodilating stimuli 2
• The condition is associated with failure of nocturnal blood pressure drops, insulin resistance, and generalized endothelial dysfunction 2

Transient Causes to Exclude

Before confirming persistent microalbuminuria, rule out these temporary elevations:

• Exercise within 24 hours of urine collection 2
• Acute infections and fever 2
• Congestive heart failure due to increased venous pressure 2
• Marked hyperglycemia even without established nephropathy 2
• Marked hypertension causing pressure-related albumin leakage 2
• Urinary tract infections with associated inflammation 2
• Hematuria and pyuria causing false elevations 2

Screening Recommendations

• Type 1 diabetes: Begin annual screening after 5 years of diabetes duration 1, 4
• Type 2 diabetes: Begin annual screening at diagnosis 1, 4
• Hypertensive patients: Screen with spot urine albumin-to-creatinine ratio 4

Common Pitfalls

• Single measurements are misleading—always confirm with multiple samples over 3-6 months 2, 8
• Do not confuse urine creatinine with serum creatinine—urine creatinine on an ACR test is merely a normalizing factor, not an assessment of kidney function 2
• Sex-specific considerations matter—men typically have higher urine creatinine excretion due to greater muscle mass 2
• Failure to use specific microalbumin assays rather than standard dipstick tests leads to missed diagnoses 2

Terminology Update

The American Diabetes Association no longer uses the terms "microalbuminuria" and "macroalbuminuria" since albuminuria occurs on a continuum, now simply defining albuminuria as UACR ≥30 mg/g. 1