Spot urine protein/creatinine ratio as a reliable estimate of 24-hour proteinuria in patients with immunoglobulin A nephropathy, but not membranous nephropathy

Abstract

Background Proteinuria is known to be associated with both kidney function deterioration and cardiovascular diseases. While proteinuria estimation from 24-h urine samples has traditionally been considered as the standard method for assessment of the degree of urinary protein excretion, sample collection is associated with several technical problems such as inaccurate collection and the potential spread of drug-resistant pathogens. Therefore, the spot urine protein/creatinine ratio (PCR) assessment is currently recommended as an alternative. While the utility of PCR has been validated, studies on the association between spot urine PCR and 24-h proteinuria (24HP) in patients with chronic glomerular nephritis (CGN) and nephrotic syndrome (NS) are limited. This study aimed to evaluate whether an estimated result from a spot urine PCR could sufficiently approximate the daily urine protein excretion amount from a 24-h urine sample in patients with immunoglobulin A nephropathy (IgAN), minimal change disease (MCD), and membranous nephropathy– nephrotic syndrome (MN-NS). Methods The study participants included 161 patients with IgAN, MCD, or MGN-NS at the Jikei University Kashiwa Hospital and Kanagawa Prefecture Shiomidai Hospital. The correlation between spot urine PCR and a 24-h urine protein was investigated using linear regression analysis with Spearman’s correlation (r) coefficient and intraclass correlation coefficient (ICC). Results While high correlation coefficients (r = 0.86, P < 0.001) and substantial agreement (ICC: 0.806, P < 0.001) were observed in patients with IgAN, similar correlations were not observed in patients with MCD or MN-NS. In the patients with MCD, r was 0.53 (P < 0.001), which signified a slight correlation, and in the patients with MN-NS, r was 0.289 ( P = 0.17), which was not statistically significant. Conclusions This study revealed that spot urine PCR is a reliable estimate of 24HP value in patients with IgAN. In contrast, there is a considerable difference between the daily urine protein excretion amount based on a 24-h urine sample and that which is calculated from spot urine PCR in patients with NS.

Diagnostic utility of protein to creatinine ratio (P/C ratio) in spot urine sample within routine clinical practice

“…A spot urine P/C ratio value of 20 mg/mmol (0.2 mg/ mg) is the most frequently reported cutoff point for determining the presence or absence of proteinuria, and a P/C ratio of 350 mg/mmol (3.5 mg/mg) is used for 5. Limitations of the spot urine P/C ratio evaluation [5,21,29,33,39,45,54,92,93,101,[113][114][115][116].…”

“…Reference Limitations [5] Spot urine P/C ratio does not take into account protein excretion in the urine during the day and from dayto-day [21] Lack of correlation between spot urine P/C ratio and protein concentration evaluated in 24-hour urine collection, if daily protein excretion exceed 6 g/day and GFR <15 mL/min/1.73m 2 [92,93] Spot urine P/C ratio result depends on ethnicity (lower values are observed in the African-Americans, because they excrete more creatinine to urine compared to Caucasians with similar height and weight) [101] Spot urine P/C ratio result depends on muscle mass, which indicates its limited use in children/patients with low muscle mass and severely undernourished (the risk of false positive results when the urine sample is excessively diluted or creatinine in the urine 2.65 mmol/L (30 mg/dL)) [54,113] Poor or lack of correlation between spot urine P/C ratio and protein concentration in 24-hour urine collection in patients with minimal change disease or membranous nephropathy with nephrotic-range proteinuria [114] The protein concentration may be overestimated or underestimated, especially when urine creatinine levels are 3.45 mmol/L (39 mg/dL) or !5.48 mmol/L (62 mg/dL) [33,115] The spot urine P/C ratio may be overestimated at GFR levels 10 mL/1.73m 2 [29,39,45,116] The diversity of methods used to assess protein and creatine concentration make the comparison of spot urine P/C ratio results between laboratories impossible GFR: glomerular filtration rate; P/C ratio: protein-creatinine ratio.…”

“…Table 6. Key points in the evaluation of the spot urine P/C ratio in different states [5,10,[12][13][14][15][16][17]21,27,[33][34][35][36][37]54,55,60,61,63,65,67,70,72,79,82,84,86,87,89,90,94,96,97,99,103,108,110,113,115,[117][118][119][120][121][122][123][124][125][126][127][128][129][130].…”

Comparing Spot Urine Protein: Creatinine Ratio 24-Hour Urinary Protein Estimation in Type 2 Diabetes Mellitus Patients

“…The age difference is not significant but that showed early onset of diabetes mellitus in our population. This could be due to multiple factors such as cousin marriages, poor dietary habits, and awareness regarding disease [12][13][14].…”

Correlation Between 24-Hour Urine Protein and Random Urine Protein-Creatinine Ratio in Amyloid Light-Chain Amyloidosis

“…Prior data have suggested the correlation between these two measurements decreases with higher levels of proteinuria. 9,10,11 Two of the previous studies investigated the use of UACR instead of 24-J o u r n a l P r e -p r o o f hr urine in AL amyloidosis patients 5,6 , however, at some institutions UACR cannot be used to quantify albuminuria >2000 mg/g, the limit placed by the manufacturer of some assays and UPCR has to be ordered instead at higher proteinuria levels. Given that many patients with AL amyloidosis have a wide range of proteinuria, often in the nephrotic range, this study is set to examine the correlation between 24-hr urine testing and UPCR at various proteinuria levels in patients with AL amyloidosis.…”