From the Guidelines
Protein/creatinine and albumin/creatinine ratios are crucial for assessing kidney function, with normal values being less than 0.2 mg/mg for PCR and less than 30 mg/g for ACR, according to the most recent guidelines 1.
Interpretation of Ratios
To interpret these ratios, it's essential to understand that they measure the amount of protein or albumin in urine relative to creatinine, which helps standardize for urine concentration.
- For protein/creatinine ratio (PCR), values above 0.2 mg/mg suggest proteinuria.
- For albumin/creatinine ratio (ACR), values between 30-300 mg/g indicate microalbuminuria, and over 300 mg/g represent macroalbuminuria or clinical proteinuria.
Clinical Utility
These ratios are particularly useful in monitoring kidney disease progression in conditions like diabetes and hypertension.
- When interpreting results, consider that transient elevations can occur with fever, exercise, or urinary tract infections, so confirmation with repeat testing is often necessary.
- The advantage of these spot urine tests is they eliminate the need for 24-hour urine collections while providing reliable estimates of protein excretion.
Prognostic Value
Higher ratios correlate with greater kidney damage and worse prognosis, making them important markers for both diagnosis and monitoring treatment effectiveness in kidney disease, as emphasized by the KDIGO guidelines 1.
- The relationships between albumin excretion rate (AER), protein excretion rate (PER), ACR, and PCR are approximate due to variations in creatinine excretion with age, sex, race, and diet.
- ACR < 10 mg/g is considered normal, while ACR 10–29 mg/g is considered ‘high normal.’
Recommendations
In clinical practice, using the albumin/creatinine ratio or total protein/creatinine ratio is recommended for monitoring proteinuria in adults with chronic kidney disease, especially when the albumin/creatinine ratio is high (>500 to 1000 mg/g) 1.
- The KDIGO guidelines provide a comprehensive framework for the evaluation and management of chronic kidney disease, including the use of protein/creatinine and albumin/creatinine ratios 1.
From the Research
Interpretation of Protein-to-Creatinine (P/C) Ratio and Albumin-to-Creatinine (A/C) Ratio
The protein-to-creatinine (P/C) ratio and albumin-to-creatinine (A/C) ratio in urine are important markers of kidney damage and are used for prognosis in persons with chronic kidney disease (CKD) 2.
- The P/C ratio and A/C ratio are relatively similar in their associations with common complications of CKD, such as lower serum hemoglobin, bicarbonate, and albumin levels and higher parathyroid hormone, phosphorus, and potassium levels 2.
- A study found that a positive semi-quantitative test for proteinuria could accurately substitute for a quantitative test to evaluate renal disease, with a positive predictive value of 91% for a test result of more than or equal to 1+ for protein 3.
- Both P/C ratio and A/C ratio are useful in evaluating proteinuria, but estimated protein excretion rate (ePER) and estimated albumin excretion rate (eAER) may be superior to A/C ratio and P/C ratio in quantifying daily proteinuria and albuminuria 4.
- Random urine P/C ratio and A/C ratio can accurately predict 24-hour protein and albumin loss in patients with kidney disease, with areas under the curve (AUC) of 0.90-0.92 for P/C ratio and 0.98-0.99 for A/C ratio 5.
- A study found that P/C ratio is a more sensitive screening test than A/C ratio to predict clinically relevant proteinuria, with a higher sensitivity (94% vs 79%) but lower specificity (88% vs 95%) than A/C ratio 6.
Comparison of P/C Ratio and A/C Ratio
- The relationship between A/C ratio and P/C ratio is non-linear, and P/C ratio is highly correlated with 24-hour urine protein (Spearman's rho = 0.91), though A/C ratio also performs well (rho = 0.84) 6.
- P/C ratio outperforms A/C ratio at predicting 0.5 g/day (AUC 0.967 vs 0.951, P < 0.001) and 1 g/day of proteinuria (AUC 0.968 vs 0.947, P = 0.004) 6.
- The diagnostic performance of both P/C ratio and A/C ratio varies substantially with age and gender, and should be taken into consideration when interpreting results 6.