From the Guidelines
Normal albuminuria is defined as a urinary albumin-to-creatinine ratio (UACR) of less than 30 mg/g creatinine. This definition is based on the most recent and highest quality study available, which emphasizes the importance of using UACR to assess albuminuria 1. The normal range for albumin excretion in urine is less than 30 mg per day or less than 20 micrograms per minute. This small amount of albumin in the urine is considered physiological and not indicative of kidney disease.
Key Points
- The kidneys filter blood and normally prevent large proteins like albumin from passing into the urine, but tiny amounts can still be excreted.
- Regular screening for albuminuria is important, especially for individuals with risk factors for kidney disease such as diabetes or hypertension.
- When albumin levels exceed the normal range (microalbuminuria at 30-300 mg/day or macroalbuminuria at >300 mg/day), it suggests kidney damage and requires medical attention.
- The presence of normal levels of albumin in urine reflects proper kidney function and intact glomerular filtration barriers that effectively prevent excessive protein leakage.
Albuminuria Categories
The American Diabetes Association (ADA) defines albuminuria categories as follows:
- Normal to mildly increased: UACR < 30 mg/g
- Moderately increased albuminuria: UACR 30-299 mg/g
- Severely increased albuminuria: UACR ≥ 300 mg/g 1
Clinical Implications
The assessment of albuminuria is crucial in the diagnosis and management of kidney disease, particularly in patients with diabetes or hypertension. Annual measurement of albuminuria is useful to assess risk and treatment 1. A sustained reduction in albuminuria of at least 30% to 50% is considered a surrogate marker of slowed progression of kidney disease.
From the Research
Definition of Normal Albuminuria
- Albuminuria is defined as the presence of albumin in the urine, which is an important risk marker for adverse cardiovascular and renal outcomes and mortality 2.
- The relationship between albuminuria and risk is continuous and linear, like that of blood pressure and cardiovascular risk 2.
- Normal albuminuria is typically defined as a urinary albumin-to-creatinine ratio (UACR) of less than 30 mg/g 3.
Measurement of Albuminuria
- Albuminuria can be measured using microalbumin-specific dipsticks or urinary albumin-to-creatinine ratio determination from a spot urine sample 2.
- The use of UACR instead of 24-hour urinary albumin excretion (UAE) for staging albuminuria has been advocated, with high agreement between the two methods 3.
- However, there may be some misclassification when using UACR instead of UAE, particularly in patients with interindividual differences in urinary creatinine excretion 3.
Comparison with Proteinuria
- Proteinuria and albuminuria are both important disease markers of chronic kidney disease (CKD) 4, 5.
- While dip-stick proteinuria correlates poorly with albumin-to-creatinine ratio (ACR), random urine protein-to-creatinine ratio (PCR) correlates reasonably well with ACR 5.
- Both proteinuria and albuminuria are good biomarkers for cardiovascular events, renal events, or mortality, but there are limitations in their use as surrogate end-points in clinical trials 5.
Clinical Significance
- The presence of albuminuria is associated with an increased risk of cardiovascular and renal outcomes, and mortality 2, 3.
- The treatment of albuminuria includes risk factor management, ongoing monitoring, and the use of renin-angiotensin-aldosterone system (RAAS)-blocking agents in patients with hypertension, chronic kidney disease, or diabetes 2.