From the Guidelines
An elevated albumin to creatinine ratio (ACR) in urine indicates the presence of albuminuria, which is an early sign of kidney damage. This finding suggests that the kidneys' filtering system is allowing abnormal amounts of albumin (a protein) to leak into the urine. According to the most recent guidelines 1, normal ACR values are generally below 30 mg/g, with 30-300 mg/g considered moderately elevated (microalbuminuria) and above 300 mg/g considered severely elevated (macroalbuminuria).
Key Points to Consider
- The ACR is a continuous measurement, and differences within the normal and abnormal ranges are associated with renal and cardiovascular outcomes 1.
- Two of three specimens of UACR collected within a 3- to 6-month period should be abnormal before considering a patient to have high or very high albuminuria 1.
- Factors such as exercise, infection, fever, congestive heart failure, marked hyperglycemia, menstruation, and marked hypertension may elevate UACR independently of kidney damage 1.
- The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation is preferred for calculating eGFR 1.
Implications of Elevated ACR
- An eGFR persistently <60 mL/min/1.73 m2 in concert with a urine albumin value of >30 mg/g creatinine is considered abnormal 1.
- The albumin-to-creatinine ratio 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.
Recommendations
- Prompt referral to a nephrologist is recommended for uncertainty about the etiology of kidney disease, difficult management issues, and rapidly progressing kidney disease 1.
- Treatment typically focuses on controlling blood pressure (often with ACE inhibitors or ARBs), optimizing blood glucose in diabetic patients, reducing dietary protein and sodium intake, and addressing other modifiable risk factors.
- Regular monitoring of ACR is important for tracking kidney function over time and evaluating response to treatment.
From the Research
Elevated Albumin to Creatinine Ratio in Urine
An elevated albumin (Alb) to creatinine (Cr) ratio (ACR) in urine is a significant indicator of kidney damage and disease progression. The following points summarize the implications of an elevated ACR:
- Definition and Threshold: A urinary albumin/creatinine ratio (UACR) <30 mg/g is considered normal, while a ratio >30 mg/g indicates an increased risk of incident hypertension and cardiovascular disease mortality 2.
- Chronic Kidney Disease (CKD) Progression: An elevated UACR is associated with the risk of developing CKD, even at levels considered within the normal range (<30 mg/g) 2. A cutoff UACR value of >10 mg/g could significantly predict the cumulative incidence and progression of CKD in patients with type 2 diabetes mellitus.
- Cardiorenal Risk: Albuminuria is a major risk factor for cardiovascular and renal disease, starting from levels not yet considered in the definition of CKD 3. An elevated ACR is a known early predictor of future cardiovascular events.
- Comparison with Protein-Creatinine Ratio (PCR): Both ACR and PCR are important markers of kidney damage, and their associations with clinical outcomes are similar 4. Routine measurement of PCR may provide similar information as ACR in managing immediate complications of CKD.
- Therapeutic Target: Albuminuria is an appropriate therapeutic target in patients with CKD, as reducing albuminuria is associated with a decrease in the rate of renal function loss 5.
- Diagnostic Accuracy: Point-of-care testing devices, such as the CLINITEK Microalbumin and DCA 2000+, can be used to rule out increased urinary albumin excretion, with high negative likelihood ratios above the 24-hour urinary albumin excretion rate of 30 mg/24 h 6.
Key findings from the studies suggest that an elevated ACR is a significant indicator of kidney damage and disease progression, and reducing albuminuria is a crucial therapeutic target in patients with CKD.