From the Guidelines
Normal albuminuria is typically less than 30 mg/g, which is equivalent to a 24-h albumin excretion rate (AER) <30 mg/day. This level indicates healthy kidney function where the glomerular filtration barrier is working properly to prevent albumin, a protein normally found in blood, from leaking into the urine in significant amounts 1. Some laboratories may report normal values as less than 20 mg/g, while others use cutoffs of 15-30 mg/g. Values between 30-300 mg/g indicate microalbuminuria, an early sign of kidney damage, while levels above 300 mg/g represent macroalbuminuria or clinical proteinuria, suggesting more significant kidney dysfunction.
Key Points to Consider
- The albumin-to-creatinine ratio (uACR) is a continuous marker for cardiovascular event risk at all levels of kidney function, and the risk starts at values that are consistently above 30 mg/g 1.
- Conventional qualitative tests (chemical strips or “dipsticks”) for proteinuria do not detect small increases in urine albumin excretion, and tests to detect low concentrations of albumin are used instead 1.
- Albumin levels in urine are important markers for monitoring kidney health, particularly in conditions like diabetes and hypertension where early detection of kidney damage can lead to interventions that slow disease progression 1.
- Regular testing is recommended for at-risk individuals to detect changes before significant kidney damage occurs, with a goal of achieving a uACR of <30 mg/g and reducing the risk of kidney disease progression 1.
Clinical Implications
- The duration of diabetes prior to puberty was reported to be an important risk factor in adolescents with type 1 diabetes and could be used to support testing prior to puberty in some individuals 1.
- A >30% sustained reduction in albuminuria is accepted as a surrogate marker of slowed progression of kidney disease at the group level, e.g., in a clinical trial 1.
- Uncommonly, an individual can have as much as 40% to 50% variability in albumin excretion, thus the focus in an individual is not only the baseline value, but the goal should be to drop uACR by at least 30% to 50% and ideally try to achieve a uACR of <30 mg/g 1.
From the Research
Definition of Normal Albuminuria
- Normal albuminuria is typically defined as a urinary albumin-creatinine ratio (UACR) less than 30 mg/g (3.4 mg/mmol) 2
- However, some studies suggest that even levels below this threshold may be associated with an increased risk of cardiovascular disease and death 3, 2
Albuminuria Levels in mg/L
- To convert UACR from mg/g to mg/L, we need to know that a normal creatinine level is around 1 g/L
- Assuming a creatinine level of 1 g/L, a UACR of 30 mg/g would be equivalent to 30 mg/L
- However, the exact conversion may vary depending on the individual's creatinine level
Risk of Cardiovascular Disease and Death
- Studies have shown that albuminuria levels within the "normal" range (< 30 mg/g) may still be associated with an increased risk of cardiovascular disease and death 3, 2
- In particular, a study found that participants with a UACR in the third and fourth quartiles (> 5.4 to < 10.2 mg/g and > 10.2 to < 30 mg/g, respectively) had a significantly higher risk of cardiovascular events and mortality compared to those in the lowest quartile (< 2.7 mg/g) 2
Clinical Implications
- These findings suggest that the traditional cutoff value for normal albuminuria (UACR < 30 mg/g) may need to be reevaluated 2
- Clinicians should be aware of the potential risks associated with albuminuria levels within the "normal" range and consider more aggressive monitoring and treatment strategies for patients with cardiovascular risk factors 3, 4