What is the difference between Albumin (Albumin) to Creatinine (Creatinine) ratio and Protein (Protein) to Creatinine (Creatinine) ratio?

From the Guidelines

Albumin-to-creatinine ratio (ACR) is the preferred method for detecting and monitoring proteinuria in patients with chronic kidney disease, as it is more sensitive for early kidney damage compared to protein-to-creatinine ratio (PCR) 1. When it comes to screening and monitoring early kidney disease, particularly diabetic nephropathy, ACR is the better choice. This is because ACR detects smaller amounts of albumin, also known as microalbuminuria, making it more sensitive for early kidney damage when intervention is most effective.

Key Differences Between ACR and PCR

• ACR detects microalbuminuria, which is an early sign of kidney damage, whereas PCR measures all proteins in urine and becomes more useful when significant proteinuria is present.
• The normal ACR is <30 mg/g, with 30-300 mg/g indicating microalbuminuria and >300 mg/g suggesting macroalbuminuria.
• PCR is typically considered abnormal above 150-200 mg/g.

Clinical Context

The choice between ACR and PCR depends on the clinical context:

• ACR is preferred for early detection and monitoring of diabetic and hypertensive kidney disease.
• PCR provides better assessment of total protein loss in established kidney disease or when non-albumin proteinuria is suspected, such as in multiple myeloma or certain tubular disorders, as stated in the guidelines for chronic kidney disease evaluation, classification, and stratification 1. Both tests require only a spot urine sample rather than 24-hour collection, improving patient compliance.

Important Considerations

• The guidelines reference a large number of articles, with 367 original articles tabulated and graded according to four dimensions: study size, applicability, and other factors 1.
• The ratio of concentration of albumin to creatinine in untimed urine samples should be used to detect and monitor proteinuria, as recommended by the national kidney foundation practice guidelines for chronic kidney disease 1.

From the Research

Comparison of Albumin Creatinine and Protein Creatinine Ratios

• The albumin creatinine ratio (ACR) and protein creatinine ratio (PCR) are both used to measure kidney damage and predict complications in patients with chronic kidney disease (CKD) 2, 3, 4, 5, 6.
• Studies have shown that ACR and PCR are correlated, but the relationship between them is non-linear 4, 5.
• ACR and PCR have similar associations with common complications of CKD, such as lower serum hemoglobin, bicarbonate, and albumin levels, and higher parathyroid hormone, phosphorus, and potassium levels 2.
• PCR may be a more sensitive screening test than ACR for predicting clinically relevant proteinuria, especially in certain patient populations such as older adults and females 5.
• Equations have been developed to estimate ACR from PCR, which may be useful in situations where only PCR is available, such as in retrospective clinical or research applications 4, 6.
• These equations have been validated in various populations and have shown good concordance between measured and estimated ACR values 6.

Clinical Implications

• The choice between ACR and PCR may depend on the specific clinical context and patient population 2, 3, 5.
• Clinicians should be aware of the potential differences in performance between ACR and PCR in different patient groups, such as those with diabetes or non-diabetic CKD 5.
• The use of equations to estimate ACR from PCR may be a useful tool in certain situations, but should be interpreted with caution and in the context of other clinical factors 4, 6.

Associations with CKD Complications

• Both ACR and PCR are associated with common complications of CKD, including cardiovascular disease and end-stage kidney disease 2, 5.
• The associations between ACR and PCR with these complications are similar, but may vary depending on the specific patient population and clinical context 2, 3, 5.