What the Microalbumin Test Measures
The microalbumin test measures small amounts of the protein albumin in urine, specifically detecting levels between 30-300 mg/24 hours (or 30-299 mg/g creatinine on a spot urine sample), which are too low to be detected by standard urine dipstick tests. 1
Clinical Significance
The test serves two critical purposes:
Early Detection of Kidney Disease
- Microalbuminuria represents the earliest clinical evidence of diabetic nephropathy and indicates damage to the glomerular filtration barrier 1, 2
- In type 1 diabetes, 80% of patients with sustained microalbuminuria will progress to overt nephropathy (≥300 mg/24h) within 10-15 years without intervention 1
- In type 2 diabetes, 20-40% with microalbuminuria progress to renal failure without treatment 1
Cardiovascular Risk Marker
- Microalbuminuria is a powerful marker of greatly increased cardiovascular morbidity and mortality in both diabetic and non-diabetic patients 1, 3
- The finding should trigger aggressive cardiovascular risk reduction including LDL cholesterol lowering, antihypertensive therapy, smoking cessation, and exercise 1
Diagnostic Thresholds
The test categorizes albumin excretion as 1, 2:
- Normal: <30 mg/g creatinine
- Microalbuminuria: 30-299 mg/g creatinine
- Clinical albuminuria (overt proteinuria): ≥300 mg/g creatinine
Testing Methodology
The preferred method is measuring the albumin-to-creatinine ratio in a random spot urine collection, ideally first-void or morning specimen due to diurnal variation in albumin excretion 1. This method is easiest to perform in office settings and provides accurate information.
Important Testing Caveats
Two of three specimens collected within a 3-6 month period must be abnormal before diagnosing microalbuminuria due to marked day-to-day variability 1.
Transient elevations can occur with 1:
- Exercise within 24 hours
- Infection or fever
- Congestive heart failure
- Marked hyperglycemia or hypertension
- Urinary tract infection
- Hematuria or pyuria
Screening Recommendations
For type 2 diabetes: Screen at diagnosis, then annually 1, 4
For type 1 diabetes: Begin screening after 5 years of disease duration, then annually 2
For hypertensive patients: The 2007 ESH/ESC guidelines recommend screening all hypertensive patients for microalbuminuria, as it predicts cardiovascular events even in non-diabetic patients 3
Standard hospital laboratory protein assays are not sufficiently sensitive to detect microalbuminuria—specific immunoassays are required 1.