From the Guidelines
The urine protein-to-creatinine ratio (UPCR) is a reliable and convenient method for estimating daily urine protein excretion 1.
Estimating Daily Urine Protein Excretion
To estimate urine protein per day from the UPCR, the following calculation can be applied:
- urine protein per day (in grams) = UPCR (in grams per gram of creatinine) x creatinine excretion rate (approximately 20-25 mg/kg body weight per day for adults) 1. For example, a UPCR of 1.5 g/g creatinine in a 70 kg adult corresponds to approximately 2.1-2.6 grams of protein per day, assuming a creatinine excretion rate of 20-25 mg/kg/day.
Clinical Application
This calculation can be useful in monitoring proteinuria in patients with kidney disease, particularly those on medications such as angiotensin-converting enzyme inhibitors (e.g., lisinopril 10-40 mg daily) or angiotensin receptor blockers (e.g., losartan 25-100 mg daily) 1.
Albuminuria Categories
According to the guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus, albuminuria categories are defined as follows:
- A1: Normal to mildly increased, <30 mg/g (<3 mg/mmol)
- A2: Moderately increased, 30-299 mg/g (3-29 mg/mmol)
- A3: Severely increased, ≥300 mg/g (≥30 mg/mmol) 1 These categories can help clinicians assess the risk of kidney disease progression and cardiovascular risk in patients with diabetes.
Key Points
- The UPCR is a reliable method for estimating daily urine protein excretion.
- The calculation for estimating daily urine protein excretion is based on the UPCR and creatinine excretion rate.
- Albuminuria categories can help clinicians assess the risk of kidney disease progression and cardiovascular risk in patients with diabetes.
From the Research
Correlation between UPCR and Daily Urine Protein Excretion
- The correlation between Urine Protein-to-Creatinine Ratio (UPCR) and daily urine protein excretion has been studied in several research papers 2, 3, 4, 5, 6.
- A study published in 2019 found a correlation coefficient of 0.819 between UPCR and 24-hour urine protein excretion 2.
- Another study published in 2022 found that the correlation between UPCR and 24-hour urine protein excretion was influenced by the level of proteinuria, with a stronger correlation at lower levels of proteinuria 3.
- The accuracy of UPCR in estimating daily urine protein excretion has been found to be influenced by urine concentration, with overestimation in dilute urine samples and underestimation in concentrated urine samples 4.
- Physical activity has also been found to affect the correlation between UPCR and daily urine protein excretion, with a stronger correlation in bedridden patients and a weaker correlation in active patients 5.
- A study published in 2009 found a very good correlation (r = 0.832, P < 0.0001) between spot urine protein-to-creatinine ratio and 24-hour urine protein excretion, but noted that the limits of agreement between the two tests became wider as protein excretion increased 6.
Factors Influencing the Correlation
- Urine concentration: UPCR may overestimate daily urine protein excretion in dilute urine samples and underestimate it in concentrated urine samples 4.
- Physical activity: The correlation between UPCR and daily urine protein excretion may be affected by the level of physical activity, with a stronger correlation in bedridden patients and a weaker correlation in active patients 5.
- Level of proteinuria: The correlation between UPCR and daily urine protein excretion may be influenced by the level of proteinuria, with a stronger correlation at lower levels of proteinuria 3.
Clinical Implications
- UPCR can be a useful tool for estimating daily urine protein excretion, but its accuracy may be influenced by several factors, including urine concentration, physical activity, and level of proteinuria 2, 3, 4, 5, 6.
- Clinicians should be aware of these factors when interpreting UPCR results and consider using additional tests, such as 24-hour urine protein excretion, to confirm the diagnosis and monitor treatment 2, 3, 6.