From the Guidelines
The normal urine protein-to-creatinine ratio (UPCR) is less than 0.2 mg/mg (or less than 20 mg/mmol if using SI units). This ratio is an important clinical measurement used to assess kidney function and detect proteinuria without requiring a 24-hour urine collection. Values above 0.2 mg/mg indicate abnormal protein excretion, with ratios between 0.2-0.5 mg/mg suggesting mild proteinuria, 0.5-3.0 mg/mg indicating moderate proteinuria, and values above 3.0 mg/mg representing severe proteinuria or nephrotic-range proteinuria. The UPCR works because creatinine excretion is relatively constant throughout the day, so measuring the protein relative to creatinine in a spot urine sample provides a reliable estimate of the 24-hour protein excretion. This test is particularly useful for monitoring kidney disease progression, assessing response to treatment, and screening for kidney damage in high-risk populations such as those with diabetes or hypertension 1.
Some key points to consider when interpreting the UPCR include:
- The ratio of concentration of albumin to creatinine in untimed urine samples should be used to detect and monitor proteinuria.
- A cutoff value for an albumin–creatinine ratio greater than 30 mg/g in men and women is recommended, with some studies suggesting sex-specific cutoff values.
- The UPCR is a useful tool for detecting chronic kidney disease, classifying its severity, estimating progression, managing complications, and deciding on referral to a nephrologist.
- The test is particularly useful in high-risk populations, such as those with diabetes or hypertension, where early detection and treatment can help prevent or delay adverse outcomes.
Overall, the UPCR is a valuable tool in the assessment and management of kidney disease, and its interpretation should be guided by the latest clinical guidelines and evidence-based recommendations 1.
From the Research
Normal Urine Protein Creatinine Ratio
The normal urine protein creatinine ratio can vary depending on several factors, including the individual's health status and the laboratory methods used.
- According to a study published in 2009 2, the spot urine protein-to-creatinine ratio can be used to estimate 24-hour urine protein excretion, with a cutoff value of 0.72 mg/mg (sensitivity 0.97; specificity 1.0) reliably predicting 24-hour urine total protein equivalent "thresholds" of 0.5 g/day.
- A study published in 2020 3 found that a urine protein/creatinine ratio (UPCR) of < 0.2 g/g Cr can be considered a criterion for normal-range proteinuria in children.
- Another study published in 2020 4 reported that a spot urine P/C ratio > 20 mg/mmol (0.2 mg/mg) is the most commonly reported cutoff value for detecting proteinuria, while a P/C ratio value > 350 mg/mmol (3.5 mg/mg) confirms nephrotic proteinuria.
Factors Affecting Urine Protein Creatinine Ratio
Several factors can affect the urine protein creatinine ratio, including:
- Urine concentration: A study published in 2015 5 found that the urine protein/creatinine ratio can be influenced by urine concentration, with dilute urine samples more likely to overestimate daily urine protein excretion and concentrated urine samples more likely to underestimate it.
- Laboratory methods: The study published in 2020 4 noted that the choice of laboratory methods for determining protein and creatinine concentrations can affect the accuracy of the P/C ratio.
Clinical Applications
The urine protein creatinine ratio has several clinical applications, including: