From the Guidelines
The albumin to creatinine ratio (ACR) is the preferred test over the protein to creatinine ratio (PCR) for detecting and monitoring kidney disease, particularly in adults at increased risk for chronic kidney disease, as recommended by the National Kidney Foundation practice guidelines 1.
Key Differences Between ACR and PCR
- ACR specifically measures albumin, which is the predominant protein in early kidney damage, making it more sensitive for detecting the earliest stages of kidney disease.
- PCR measures all proteins in urine and becomes more useful in conditions with significant proteinuria or when non-albumin proteins are present.
- The normal ACR is less than 30 mg/g, with 30-300 mg/g indicating microalbuminuria and values above 300 mg/g representing macroalbuminuria, as opposed to PCR which is typically considered abnormal above 150-200 mg/g.
Clinical Implications
- Clinicians should use ACR for diabetes screening and early chronic kidney disease detection, while reserving PCR for established kidney disease with heavy proteinuria, as suggested by the guidelines 1.
- The difference between ACR and PCR matters because albumin leakage specifically indicates glomerular damage, while total protein elevation may reflect various types of kidney injury.
- Both tests require a spot urine sample rather than 24-hour collection, making them convenient for routine clinical practice, though results should be confirmed with repeat testing due to potential day-to-day variability.
Recommendations for Practice
- Adults at increased risk for chronic kidney disease, especially those with diabetes, should undergo testing with either an albumin-specific dipstick or an untimed urine measurement for the albumin–creatinine ratio, as recommended by the National Kidney Foundation practice guidelines 1.
- Monitoring proteinuria in adults with chronic kidney disease should use the albumin–creatinine ratio or total protein-creatinine ratio if the albumin–creatinine ratio is high (>500 to 1000 mg/g), according to the guidelines 1.
From the Research
Significance of Albumin to Creatinine Ratio versus Protein to Creatinine Ratio
- The albumin to creatinine ratio (ACR) and protein to creatinine ratio (PCR) are both important markers of kidney damage and are used for prognosis in persons with chronic kidney disease (CKD) 2.
- Studies have shown that ACR and PCR are relatively similar in their associations with common complications of CKD, such as serum hemoglobin, bicarbonate, parathyroid hormone, phosphorus, potassium, and albumin levels 2.
- The performance of calculated versus measured ACR in predicting kidney failure and death in people with CKD has been evaluated, with results suggesting that calculated ACR can be used for risk predictions when measured ACR is not available 3.
- PCR-calculated ACR may have superior performance to dipstick-calculated ACR, with closer agreement between predictions based on measured versus PCR-calculated ACR 3.
Comparison of ACR and PCR
- ACR and PCR have similar associations with CKD complications, with only small absolute differences in outcome measures 2.
- The use of ACR or PCR may depend on the specific clinical context and the availability of measurements 2.
- Equations have been developed to estimate ACR from PCR, which may be useful in situations where only PCR is available 4, 5.
- These equations have been validated using same-day measurements of ACR and PCR, with good concordance between measured and estimated ACR 4.
Clinical Implications
- Routine measurement of PCR may provide similar information as ACR in managing immediate complications of CKD 2.
- The use of ACR or PCR should be guided by clinical judgment and the specific needs of the patient 2.
- Further research is needed to fully understand the relationships between ACR, PCR, and CKD outcomes, and to develop more accurate equations for estimating ACR from PCR 3, 4, 5.