From the Guidelines
The normal range for the urine Protein-to-Creatinine (P/C) ratio is less than 150 mg/g or less than 15 mg/mmol 1.
Key Points
- A urine P/C ratio of less than 150 mg/g or less than 15 mg/mmol is considered normal to mildly increased albuminuria 1.
- This is equivalent to a 24-h albumin excretion rate (AER) less than 30 mg/day 1.
- The American Diabetes Association recommends using the urine albumin-to-creatinine ratio (uACR) to screen for albuminuria, with a threshold of less than 30 mg/g or less than 3 mg/mmol for normal to mildly increased albuminuria 1.
- It's worth noting that conventional qualitative tests for proteinuria may not detect small increases in urine albumin excretion, and tests to detect low concentrations of albumin are used instead 1.
Clinical Implications
- In clinical practice, a urine P/C ratio of less than 150 mg/g or less than 15 mg/mmol can be used as a threshold to rule out significant proteinuria 1.
- Values above 500 mg/g or 50 mg/mmol are generally indicative of severely increased albuminuria, which may require further evaluation and potential treatment 1.
From the Research
Normal Range for Urine Protein-to-Creatinine (P/C) Ratio
The normal range for the urine Protein-to-Creatinine (P/C) ratio can vary depending on the population being studied and the specific criteria used to define normal values.
- A study published in 2021 2 found that the 95th percentile of the UPCR was 141.7 mg/g for the entire cohort, 128.7 mg/g for men, and 150.8 mg/g for women.
- Another study published in 2009 3 found that the spot urine protein-to-creatinine ratio of 0.72 mg/mg reliably predicted 24-hour urine total protein equivalent "thresholds" of 0.5 g/day.
- A study published in 1995 4 found that the log random urine P/C ratio correlated to log 24 UP (r = 0.90), but the standard deviations associated with these predictions were large, especially at the higher 24 UP values.
- It's also important to note that the accuracy of the UPCR can be influenced by urine concentration, with dilute urine samples potentially leading to overestimation and concentrated urine samples potentially leading to underestimation 5.
Factors Influencing the P/C Ratio
Several factors can influence the P/C ratio, including:
- Urine concentration: Dilute urine samples can lead to overestimation, while concentrated urine samples can lead to underestimation 5.
- Sex: Women tend to have higher UPCR values than men 2.
- Age: UPCR values can vary with age, but the specific relationship is not well established.
- Kidney function: The P/C ratio can be affected by kidney function, with higher values potentially indicating kidney damage or disease.
Clinical Applications
The P/C ratio is commonly used in clinical practice to estimate daily urine protein excretion and diagnose proteinuric renal disease.
- A study published in 2024 6 found that a random UPCR screen positive threshold of 0.18 mg/dL maximizes sensitivity to identify clinically significant proteinuria.
- The P/C ratio can be used to monitor kidney function and disease progression in patients with kidney disease.
- However, the results should be interpreted with caution, especially in cases involving dilute urine samples, as overestimation may lead to an erroneous diagnosis or incorrect staging of chronic kidney disease 5.