What does an elevated urine protein-to-creatinine ratio indicate about someone's kidney function regarding Impaired renal function?

From the Guidelines

Elevated urine protein-to-creatinine ratio is a strong indicator of impaired renal function.

Implications of Elevated Ratio

• An elevated urine protein-to-creatinine ratio suggests that the kidneys are not functioning properly, leading to an excessive amount of protein in the urine 1.
• This can be a sign of kidney damage or disease, such as chronic kidney disease (CKD), diabetic nephropathy, or glomerular disease 1.
• The ratio of protein or albumin to creatinine in an untimed urine specimen is a preferred method for measuring proteinuria, as it corrects for variations in urinary protein concentration due to hydration 1.

Clinical Considerations

• The American Diabetes Association and the National Kidney Foundation recommend assessing proteinuria to detect CKD 1.
• The ratio of protein or albumin to creatinine in an untimed urine sample is an accurate estimate of the protein or albumin excretion rate 1.
• Clinicians should be educated on the various factors that can affect urinary albumin or total protein measurement, such as exercise, urinary tract infection, and preanalytical storage conditions 1.

Key Points

• Elevated urine protein-to-creatinine ratio indicates impaired renal function 1.
• The ratio is a preferred method for measuring proteinuria due to its convenience and accuracy 1.
• Clinicians should consider various factors that can affect urinary albumin or total protein measurement when interpreting results 1.

From the Research

Impaired Renal Function and Urine Protein-to-Creatinine Ratio

An elevated urine protein-to-creatinine ratio is a significant indicator of impaired renal function. The following points highlight the relationship between this ratio and kidney function:

• Proteinuria is a cardinal sign of renal disease, and accurate measurement of proteinuria is essential for diagnosing and managing kidney disease 2.
• The urine protein-to-creatinine ratio (uPCR) is a reliable estimator of 24-hour proteinuria in patients with kidney diseases, with excellent concordance between 24-hour protein excretion and uPCR 3.
• However, the accuracy of uPCR can be influenced by urine concentration, with dilute urine samples potentially leading to overestimation and concentrated urine samples leading to underestimation of daily urine protein excretion 4.

Factors Affecting Urine Protein-to-Creatinine Ratio

Several factors can affect the urine protein-to-creatinine ratio, including:

• Renal function: uPCR increases progressively as renal function deteriorates 5.
• Co-morbidities: diabetes and hyperuricemia are associated with increased uPCR, while male gender and estimated glomerular filtration rate (eGFR) are inversely related to uPCR 5.
• Urine concentration: uPCR results should be interpreted with caution in cases involving dilute urine samples, as overestimation may lead to an erroneous diagnosis of proteinuric renal disease or incorrect staging of chronic kidney disease 4.

Clinical Applications

The urine protein-to-creatinine ratio has several clinical applications:

• Screening and longitudinal testing for proteinuria: uPCR is a useful and convenient test for proteinuria, with high sensitivity and specificity values for estimating proteinuria from 0.5 to 2 g/day 6.
• Predicting renal outcome: uPCR has been shown to predict all-cause mortality, commencement of renal replacement therapy, and doubling of serum creatinine 2.