From the Guidelines
The protein-to-creatinine (P/C) ratio in urine is a crucial diagnostic tool for detecting kidney damage or disease, with a normal range of less than 200 mg/g, as indicated by the ratio of concentrations of total urine protein to urine creatinine 1. The P/C ratio is significant because it measures the amount of protein relative to creatinine in a urine sample, helping to identify abnormal protein excretion. This test is particularly useful for monitoring conditions like diabetic nephropathy, preeclampsia during pregnancy, and chronic kidney disease.
- The ratio works because creatinine is excreted at a relatively constant rate, so comparing protein to creatinine helps account for variations in urine concentration.
- This makes it more reliable than measuring protein alone and more convenient than a 24-hour urine collection.
- Elevated ratios may indicate glomerular damage, allowing protein to leak into urine, while very high ratios suggest significant kidney damage. Key points to consider when interpreting the P/C ratio include:
- At very high levels of proteinuria (spot urine total protein to creatinine ratio 500 to 1,000 mg/g), measurement of total protein, instead of albumin, on a spot urine sample is acceptable, as reported by the National Kidney Foundation (NKF) and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) 1. Regular monitoring of this ratio helps healthcare providers track kidney function over time and adjust treatment plans accordingly, ultimately impacting morbidity, mortality, and quality of life.
From the Research
Definition and Purpose of Protein-to-Creatinine (P/C) Ratio
- The protein-to-creatinine (P/C) ratio in urine is a measure used to quantify proteinuria, which is the presence of excess proteins in the urine 2.
- This ratio is calculated by dividing the amount of protein in a urine sample by the amount of creatinine in the same sample 3.
- The P/C ratio is used as a predictor of quantitation of proteinuria and is commonly used in the diagnosis of kidney diseases, detection of treatment effects, and evaluation of prognosis 2.
Clinical Significance and Interpretation
- A persistently increased protein excretion is usually a marker of kidney damage 2.
- The correlation between P/C ratio in spot urine specimens and urinary protein excretion in 24-hour collections is highly significant for patients with creatinine clearance (Ccr) greater than 10 ml/min 2.
- The P/C ratio can be used as an alternative to urine protein excretion in 24-hour collections in patients with Ccr > 10 ml/min 2.
- The cutoff values of P/C ratio for screening urinary protein excretion of 1 and 3 g in 24-hour collections were determined by receiver operating characteristics (ROC) curve analysis [(2,3)].
Comparison with Other Measures
- The P/C ratio is highly correlated with 24-hour urine protein, and it outperforms albumin-to-creatinine ratio (ACR) at predicting 0.5 g/day and 1 g/day of proteinuria 4.
- A study found that the semi-quantitative urine P/C ratio had the best sensitivity and specificity, as well as the lowest underestimation rate, compared to other laboratory methods 5.
- Equations have been developed to estimate ACR from P/C ratio, allowing for the use of P/C ratio in situations where ACR is not available 6.