From the Guidelines
The microalbumin-to-creatinine ratio is a critical measure to detect early kidney damage, with a normal ratio being less than 30 mg/g, microalbuminuria between 30-300 mg/g, and macroalbuminuria above 300 mg/g, as defined in the most recent guidelines 1.
Importance of Microalbumin-to-Creatinine Ratio
The microalbumin-to-creatinine ratio is a laboratory test that measures the amount of albumin (a protein) in urine compared to creatinine, helping to detect early kidney damage. This test is primarily used to screen for and monitor diabetic nephropathy, but it's also valuable for assessing kidney function in people with hypertension or other conditions that may affect the kidneys.
Definitions and Interpretations
- Normal: Less than 30 mg/g
- Microalbuminuria (Early Kidney Damage): 30-300 mg/g
- Macroalbuminuria (More Advanced Kidney Damage): Above 300 mg/g
Testing Recommendations
For accurate results, a random spot urine sample is typically sufficient, though first-morning samples may be preferred. Regular testing is recommended annually for diabetic patients and those with hypertension to detect kidney problems early when treatment can be most effective in preventing progression to kidney failure, as emphasized in recent care standards 1.
Clinical Application
The test works by comparing albumin to creatinine to account for urine concentration variations, providing a more reliable measure than albumin alone. At least two of three tests measured within a specific period should show elevated levels before a patient is designated as having microalbuminuria, considering factors like exercise, infection, and marked hyperglycemia that may temporarily elevate urinary albumin excretion 1.
From the Research
Microalbumin to Creatinine Ratio
The microalbumin to creatinine ratio is a measure used to detect microalbuminuria, which is defined as a persistent elevation of albumin in the urine of 30-300 mg/day (20-200 microg/min) 2, 3. This ratio is calculated by measuring the amount of albumin and creatinine in a spot morning urine sample.
Normal and Abnormal Values
A value above 0.03 mg/mg suggests that albumin excretion is above 30 mg/day and therefore microalbuminuria is present 2. However, some studies suggest that even lower levels of albuminuria, below 30 mg/g, can be associated with increased risk of incident hypertension and cardiovascular disease mortality 4, 5.
Measurement and Interpretation
The albumin-to-creatinine ratio is recommended as the preferred screening strategy for all diabetic patients and patients with hypertension 2, 3. The ratio is typically measured in spot morning urine obtained from the patient in the office and sent for measurement of both albumin and creatinine.
Key Findings
- Microalbuminuria is an established risk factor for renal disease progression in type 1 diabetes and its presence is the earliest clinical sign of diabetic nephropathy 2.
- The presence of microalbuminuria is a marker of endothelial dysfunction and a predictor of increased cardiovascular risk 2, 3.
- Microalbuminuria can be reduced, and progression to overt proteinuria prevented, by aggressive blood pressure reduction, especially with a regimen based on medications that block the renin-angiotensin-aldosterone system, and control of diabetes 2, 3.
- A cutoff UACR value of >10 mg/g could significantly predict the cumulative incidence and progression of CKD in patients with T2DM 4.
- Low levels of albuminuria, UACR below 30 mg/g, are associated with increased risk of incident hypertension and CVD mortality at follow-up, but are not associated with increased risk of incident diabetes mellitus 5.