When to use urine albumin (Albumin-to-Creatinine Ratio) versus urine protein (Protein-to-Creatinine Ratio)?

From the Guidelines

Urine albumin-to-creatinine ratio (UACR) should be used for screening and monitoring diabetic kidney disease and early detection of kidney damage, while urine protein-to-creatinine ratio (UPCR) is preferred for evaluating non-diabetic kidney diseases, nephrotic syndrome, and more advanced kidney damage. This recommendation is based on the most recent guidelines from the Diabetes Care journal, which suggest that UACR is more sensitive for detecting small amounts of albumin (microalbuminuria of 30-300 mg/g), making it ideal for early kidney disease detection, particularly in diabetes where glomerular damage initially causes albumin leakage 1. The guidelines also recommend annual measurement of UACR in adults with diabetes, and more frequent measurement (every 6 months) in patients with estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2 and/or albuminuria >30 mg/g creatinine in a spot urine sample 1. In contrast, UPCR measures all proteins in urine and is better for conditions where proteins other than albumin are excreted or when protein excretion is higher (>500 mg/day) 1. For practical application, order UACR for diabetic patients, hypertensive patients for early detection, and those at risk for early kidney disease. Order UPCR for patients with suspected glomerulonephritis, nephrotic syndrome, multiple myeloma, or established kidney disease. Key points to consider when choosing between UACR and UPCR include:

• The type of kidney disease being evaluated (diabetic vs non-diabetic)
• The stage of kidney disease (early vs advanced)
• The presence of other conditions that may affect protein excretion (e.g. hypertension, glomerulonephritis)
• The need for sensitive detection of small amounts of albumin (microalbuminuria) vs measurement of total protein excretion.

From the Research

Urine Albumin (Albumin-to-Creatinine Ratio) vs Urine Protein (Protein-to-Creatinine Ratio)

• Urine albumin-to-creatinine ratio (UACR) is a sensitive and early indicator of kidney damage, which should be used routinely to accurately assess CKD stage and monitor kidney health 2.
• Measuring albuminuria is the preferred method for defining and staging chronic kidney disease (CKD), but total urine protein or dipstick protein is often measured instead 3.
• Equations to convert urine protein-creatinine ratio (PCR) and dipstick protein to urine albumin-creatinine ratio (ACR) have been developed and tested for purposes of CKD screening and staging 3.
• The association between PCR and ACR is inconsistent for PCR values less than 50 mg/g, but for higher PCR values, the PCR conversion equations demonstrate moderate sensitivity and specificity for screening and classification into stages A2 and A3 3.
• In persons with CKD, ACR and PCR are relatively similar in their associations with common complications of CKD, suggesting that routine measurement of PCR may provide similar information as ACR in managing immediate complications of CKD 4.
• Current guidelines recommend the use of the albumin/creatinine ratio (ACR) as a surrogate for the error-prone collection of timed urine samples, but there are considerable intermethod differences for both albumin and creatinine measurement 5, 6.
• Clinical needs have been identified for standardization of urine collection methods, urine albumin and creatinine measurements, reporting of test results, and reference intervals for the ACR 5, 6.

Choosing Between UACR and PCR

• UACR is the preferred measure of albuminuria, but if ACR is not available, predicted ACR from PCR or urine dipstick protein may help in CKD screening, staging, and prognosis 3.
• The choice between UACR and PCR may depend on the specific clinical context and the availability of testing methods, but both measures can provide valuable information for managing CKD 2, 4.

Limitations and Future Directions

• The chemistry of albumin in urine is incompletely understood, and there are no reference measurement procedures for albumin and no reference materials for either analyte in urine 5, 6.
• Further research is needed to standardize urine collection methods, urine albumin and creatinine measurements, and reporting of test results to improve the accuracy and reliability of UACR and PCR measurements 5, 6.