From the Guidelines
The main difference between UPCR (Urine Protein-to-Creatinine Ratio) and ACR (Albumin-to-Creatinine Ratio) is what they measure and their clinical applications, with ACR being more sensitive for detecting early kidney damage and preferred for screening and monitoring diabetic kidney disease, as recommended by the National Kidney Foundation guidelines 1.
Key Differences
- UPCR measures the ratio of total protein to creatinine in urine, detecting all types of protein.
- ACR specifically measures albumin, which is the predominant protein in glomerular diseases.
Clinical Applications
- ACR is more sensitive for detecting early kidney damage, particularly in conditions like diabetic nephropathy.
- UPCR is better for conditions where non-albumin proteins may be present, such as multiple myeloma or tubular disorders.
Testing and Interpretation
- Both tests are performed on spot urine samples, eliminating the need for 24-hour collections.
- Both are expressed as mg/g or mg/mmol.
- Normal ACR is <30 mg/g, while normal UPCR is <150 mg/g.
Guideline Recommendations
- The National Kidney Foundation guidelines recommend using the albumin-to-creatinine ratio or total protein-to-creatinine ratio to detect and monitor proteinuria 1.
- The guidelines suggest that ACR is a more sensitive marker for chronic kidney disease due to diabetes, glomerular disease, and hypertension.
Choice of Test
- The choice between UPCR and ACR depends on the suspected kidney condition, with ACR being more specific for glomerular damage and UPCR providing a broader assessment of protein excretion.
From the Research
Difference between Urine Protein-to-Creatinine Ratio (UPCR) and Albumin-to-Creatinine Ratio (ACR)
- UPCR measures the total amount of protein in the urine, including both albumin and non-albumin proteins, whereas ACR specifically measures the amount of albumin in the urine 2, 3, 4.
- UPCR has been shown to have a superior performance to ACR in predicting 24-hour total proteinuria, which is the measurement on which the evidence for interventions in chronic kidney disease is based 2.
- ACR is measured using an immunoassay, which may be technically superior but is not without shortcomings, such as antigen excess, and is 2-10 times more expensive than UPCR 2.
- Both UPCR and ACR are effective in predicting renal outcomes and mortality in patients with chronic kidney disease (CKD), with similar adjusted hazard ratios for death, start of renal replacement therapy, and doubling of serum creatinine level 3, 4.
- UPCR takes into account non-albumin proteinuria, which has been shown to have prognostic significance, whereas ACR only measures albuminuria 2, 5.
- The association between UPCR and ACR with common complications of CKD, such as serum hemoglobin, bicarbonate, parathyroid hormone, phosphorus, potassium, and albumin levels, is similar, with only small absolute differences in the outcome measure 4.
- Measuring UPCR and ACR in spot urine is a reliable and convenient alternative to 24-hour urine collection, especially in children with podocytopathies such as Alport syndrome 5.