Spot urine protein/creatinine ratios are unreliable estimates of 24 h proteinuria in most systemic lupus erythematosus nephritis flares

Measuring albuminuria or proteinuria: does one answer fit all?

Measurement of proteinuria is critical for diagnosing and monitoring kidney disease. A variety of measures are available to clinicians and can identify all urinary proteins (proteinuria) or urine albumin alone (albuminuria). Proteinuria and albuminuria can be measured in either a random urine sample or a timed urine collection (often over 24 hours). Although an international guideline advocates the use of the urinary albumin-to-creatinine ratio for most purposes, this measure is not universally available worldwide and historically has been more costly than alternatives. In addition, there may be important differences in accuracy between the albumin-to-creatinine ratio and others based on magnitude of albuminuria, sex, and certain clinical contexts. In this mini review, we review recommendations from international guidelines and discuss specific contexts where the optimal measure of proteinuria is unclear and, in some situations, controversial. We discuss the evidence supporting current recommendations for choice of measure, including the clinical settings of glomerulonephritis, transplantation, and pregnancy. We also discuss how patient sex and cost may impact this decision.

Comparison of Urinary Protein/Creatinine Ratio as an Alternative to 24-h Proteinuria in Lupus Nephritis: TUNARI Study

BACKGROUND

Lupus nephritis (LN) occurs in approximately 50% of people with systemic lupus erythematosus (SLE). The 24-h proteinuria (gold standard) is measured among other tests for the control and monitoring of LN activity. This study investigates the use of the protein/creatinine ratio (PCR) as an alternative for the detection of proteinuria and its accuracy compared to the gold standard in a predominantly non-white population.

METHODS

This was a prospective study conducted in Salvador, Brazil, between December 2021 and May 2022. We invited adult patients diagnosed with SLE and LN, regardless of their disease activity. The estimation of the PCR and 24-h proteinuria was performed using conventional methods. The analysis used was Spearman's r correlation coefficient (rs), coefficient of determination (r2), and concordance by the Bland-Altman method. A specific sensitivity was measured by the ROC curve with its respective cut-off by the Youden Index.

RESULTS

We compared 112 samples of 75 patients with LN, with a mean age of 34.5 ± 11.8 years. Of these patients, 85% were women, 87.9% were non-white. A high degree of correlation was observed between PCR with 24-h proteinuria (rs = 0.77 and r2 = 0.59). The ROC analysis shows an area under the curve of 0.92 and the cut-off point calculated by the Youden Index was 0.78 with a sensitivity of 90.0% and specificity of 82%. However, the Bland-Altman graph indicated decreasing concordance as the degree of proteinuria increased, despite showing concordance at high levels of proteinuria.

CONCLUSION

The PCR shows high sensitivity to follow-up patients with LN when compared with 24-h proteinuria. Our findings suggest that PCR is a useful parameter for the evaluating and monitoring patients in complete remission. However, in cases of partial remission, the utility of PCR is limited.

An equation to estimate 24-hour total urine protein excretion rate in patients who underwent urine protein testing

Background

The urine protein-creatinine ratio (UPCR) in a spot first-morning urine sample is used to estimate 24-h urine proteinuria (24hUP) in patients who underwent urine protein testing. UPCR cannot be directly compared with 24-h proteinuria. Thus, an equation to estimate 24-h total protein excretion rate, using age, gender, and the UPCR may improve its bias and accuracy in patients who underwent urine protein testing.

Methods

We simultaneously measured 24-h urine protein and the same day’s first-morning spot urine from patients with kidney disease. Generalized linear and no-linear models, using age, gender, and UPCR, were constructed to estimate for 24-h urine protein and the best model (NJ equation) was selected to estimated 24 hUP (e24hUP).

Results

A total of 5435 paired samples (including a training cohort of 3803 patients and a validation cohort of 1632 patients) were simultaneously measured for UPCR and 24-h urine protein. In the training cohort, the unadjusted UPCR obviously underestimated 24-h urine protein when UPCR ≤1.2 g/g (median bias − 0.17 g/24 h) and overestimated 24-h urine protein when UPCR > 1.2 g/g (median bias 0.53 g/24 h). In the validation cohort, the NJ equation performed better than the unadjusted UPCR, with lower root mean square error (0.81 vs. 1.02, P < 0.001), less bias (median difference between measured and estimated urine protein, − 0.008 vs. 0.12), improved precision (interquartile range of the differences, 0.34 vs. 0.50), and greater accuracy (percentage of estimated urine protein within 30% of measured urine protein, 53.4% vs. 32.2%). Bland-Altman plot indicated that the agreement of spot and daily estimates was less pronounced with 24 hUP > 2 g than lower values.

Conclusions

The NJ e24hUP equation is more accurate than unadjusted UPCR to estimate 24 hUP in patients with kidney disease and could be used for laboratory application.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-022-02673-2.

Which Is a Better Predictor of GFR Decline: 24-h Urine Protein or 24-h Protein-Creatinine Ratio? An Exploration of the MDRD Study Data

Background

Proteinuria is a known risk factor for progression of chronic kidney disease. Proteinuria magnitude can be estimated by measuring spot urine protein-to-creatinine ratio (least accurate), 24-h urine collection for protein (24 P), or 24-h protein-creatinine ratio (24 PCR). The MDRD study found that 24 P measured at baseline was the strongest single predictor of the rate of GFR decline during study follow-up. However, predictive powers of 24 P and 24 PCR have not been compared in the literature. The current study addresses this question using the MDRD cohort data.

Methods

The study is a retrospective analysis of prospectively collected data from the MDRD cohort using simple and multiple regression models. Slope of measured GFR (mGFR) over time was used as the response and models that included baseline 24 PCR or 24 P were compared for the entire sample and for subgroups formed by restricting the values of 24-h creatinine and 24 P.

Results

Log 24 P and Log 24 PCR correlated almost equally with mGFR slope. However, in simple linear regression models and multivariable linear regression models adjusting for age and sex, the model with 24 PCR had a higher R 2 than the corresponding one that had 24 P except for the subgroup 24 P < 1 g.

Conclusion

We observe that 24 PCR may be a better marker of proteinuria magnitude in predicting decline in kidney function compared to 24 P in particular for patients with 24 P ≥ 1. This finding needs validation in prospective clinical trials.

Phase II, randomised, double-blind, multicentre study evaluating the safety and efficacy of filgotinib and lanraplenib in patients with lupus membranous nephropathy

Objectives

Patients with lupus membranous nephropathy (LMN) are at risk for prolonged proteinuria and progressive chronic kidney disease. There are no proven effective treatments for LMN, and controlled trials are lacking. This trial assessed the preferential Janus kinase 1 (JAK1) inhibitor filgotinib and the spleen tyrosine kinase inhibitor lanraplenib in patients with LMN.

Methods

This was a phase II, randomised, double-blind trial conducted at 15 centres in the USA to evaluate the safety and efficacy of filgotinib or lanraplenib for the treatment of LMN. Eligible patients were randomised 1:1 to receive either filgotinib or lanraplenib in a blinded fashion for up to 52 weeks. The primary endpoint was the per cent change in 24-hour urine protein from baseline to week 16.

Results

Nine patients were randomised to receive filgotinib (n=5) or lanraplenib (n=4). Four patients in the filgotinib group and one patient in the lanraplenib group completed week 16. There was a median reduction of 50.7% in 24-hour urine protein after 16 weeks of treatment with filgotinib (n=4), and the median Systemic Lupus Erythematosus Disease Activity Index from the Safety of Estrogens in Lupus National Assessment score remained stable. Filgotinib treatment was well tolerated. Limited conclusions can be drawn about treatment with lanraplenib.

Conclusion

The number of patients treated in this study was small, and only limited conclusions can be drawn. There may be a therapeutic benefit with filgotinib treatment, which may support future investigations with filgotinib or other JAK inhibitors in patients with LMN.

Trial registration number

NCT03285711.

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

The spot (random) urine protein to creatinine ratio (P/C ratio) is an alternative, fast and simple method of detecting and estimating the quantitative assessment of proteinuria. The aim of the work was to review the literature concerning the usefulness of spot urine P/C ratio evaluation in the diagnosis of proteinuria in the course of kidney disease, hypertension, gestational hypertension, preeclampsia, immunological diseases, diabetes mellitus, and multiple myeloma, and in the diagnosis of proteinuria in children. We searched the PubMed and Google Scholar databases using the following keywords: proteinuria, spot urine protein to creatinine ratio, spot urine P/C ratio, protein creatinine index, PCR (protein to creatinine ratio), P/C ratio and methods, Jaffe versus enzymatic creatinine methods, urine protein methods, spot urine protein to creatinine ratio versus ACR (albumin to creatinine ratio), proteinuria versus albuminuria, limitations of the P/C ratio. More weight was given to the articles published in the last 10-20 years. 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. The International Society for the Study of Hypertension in Pregnancy recommends a P/C ratio of 30 mg/mmol (0.3 mg/mg) for the classification of proteinuria in pregnant women at risk of preeclampsia. A high degree of correlation was observed between P/C ratio values and the protein concentration in 24-h urine collections. The spot urine P/C ratio is a quick and reliable test that can eliminate the need for a daily 24-h urine collection. However, in doubtful situations, it is still recommended to assess proteinuria in a 24-h urine collection. The literature review indicates the usefulness of the spot P/C ratio in various disease states; therefore, this test should be available in every laboratory. However, the challenge for the primary care physician is to know the limitations of the methods used to determine the protein and creatinine concentrations that are used to calculate the P/C ratio. Moreover, the P/C ratio cutoff used should be determined in individual laboratories because it depends on the patient population and the laboratory methodologies.

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

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.

Proteomic profiling of urine: implications for lupus nephritis

INTRODUCTION

Lupus nephritis (LN) is a common and significant manifestation, affecting 60% of adults and 80% of children with systemic lupus erythematosus, with up to 30% of patients progressing to end stage renal disease. There remains an unmet need for non-invasive markers of disease activity, damage, and response to therapy. In addition, non-invasive biomarkers that predict therapeutic efficacy are needed to enable cost-effective clinical trials of novel agents. Areas covered: This review examines the methodological aspects of urinary proteomics, the role of proteome profiling in identifying promising urinary biomarkers in LN, and the translation of research findings into clinically useful tools in the management of LN. Expert opinion: Targeted and unbiased proteomics have identified several promising urinary biomarkers that predict LN activity, damage (chronicity), and response to therapy. In particular, a combination of biologically plausible urinary biomarkers termed as RAIL (Renal Activity Index for Lupus) has emerged as an excellent predictor of LN activity as well as response to therapy, being able to predict efficacy within 3 months of therapy. If validated in additional large prospective studies, the RAIL biomarkers will transform the care of patients with LN, allowing for a personalized and predictive approach and improved outcomes.

Establishing Surrogate Kidney End Points for Lupus Nephritis Clinical Trials: Development and Validation of a Novel Approach to Predict Future Kidney Outcomes

OBJECTIVE

End points currently used in lupus nephritis (LN) clinical trials lack uniformity and questionably reflect long-term kidney survival. This study was undertaken to identify short-term end points that predict long-term kidney outcomes for use in clinical trials.

METHODS

A database of 944 patients with LN was assembled from 3 clinical trials and 12 longitudinal cohorts. Variables from the first 12 months of treatment after diagnosis of active LN (prediction period) were assessed as potential predictors of long-term outcomes in a 36-month follow-up period. The long-term outcomes examined were new or progressive chronic kidney disease (CKD), severe kidney injury (SKI), and the need for permanent renal replacement therapy (RRT). To predict the risk for each outcome, hazard index tools (HITs) were derived using multivariable analysis with Cox proportional hazards regression.

RESULTS

Among 550 eligible subjects, 54 CKD, 55 SKI, and 22 RRT events occurred. Variables in the final CKD HIT were prediction-period CKD status, 12-month proteinuria, and 12-month serum creatinine level. The SKI HIT variables included prediction-period CKD status, International Society of Nephrology (ISN)/Renal Pathology Society (RPS) class, 12-month proteinuria, 12-month serum creatinine level, race, and an interaction between ISN/RPS class and 12-month proteinuria. The RRT HIT included age at diagnosis, 12-month proteinuria, and 12-month serum creatinine level. Each HIT validated well internally (c-indices 0.84-0.92) and in an independent LN cohort (c-indices 0.89-0.92).

CONCLUSION

HITs, derived from short-term kidney responses to treatment, correlate with long-term kidney outcomes, and now must be validated as surrogate end points for LN clinical trials.

Urine biomarkers of chronic kidney damage and renal functional decline in childhood-onset systemic lupus erythematosus

OBJECTIVES

To delineate urine biomarkers that reflect kidney structural damage and predict renal functional decline in pediatric lupus nephritis (LN).

METHODS

In this prospective study, we evaluated kidney biopsies and urine samples of 89 patients with pediatric LN. Urinary levels of 10 biomarkers [adiponectin, ceruloplasmin, kidney injury molecule-1, monocyte chemotactic protein-1, neutrophil gelatinase-associated lipocalin, osteopontin, transforming growth factor-ß (TGFß), vitamin-D binding protein, liver fatty acid binding protein (LFABP), and transferrin] were measured. Regression analysis was used to identify individual and combinations of biomarkers that determine LN damage status [NIH-chronicity index (NIH-CI) score ≤ 1 vs. ≥ 2] both individually and in combination, and biomarker levels were compared for patients with vs. without renal functional decline, i.e., a 20% reduction of the glomerular filtration rate (GFR) within 12 months of a kidney biopsy.

RESULTS

Adiponectin, LFABP, and osteopontin levels differed significantly with select histological damage features considered in the NIH-CI. The GFR was associated with NIH-CI scores [Pearson correlation coefficient (r) = - 0.49; p < 0.0001] but not proteinuria (r = 0.20; p > 0.05). Similar to the GFR [area under the ROC curve (AUC) = 0.72; p < 0.01], combinations of osteopontin and adiponectin levels showed moderate accuracy [AUC = 0.75; p = 0.003] in discriminating patients by LN damage status. Renal functional decline occurred more commonly with continuously higher levels of the biomarkers, especially of TGFß, transferrin, and LFABP.

CONCLUSION

In combination, urinary levels of adiponectin and osteopontin predict chronic LN damage with similar accuracy as the GFR. Ongoing LN activity as reflected by high levels of LN activity biomarkers heralds renal functional decline.

KEY MESSAGES

• Levels of osteopontin and adiponectin measured at the time of kidney biopsy are good predictors of histological damage with lupus nephritis. • Only about 20% of children with substantial kidney damage from lupus nephritis will have an abnormally low urine creatinine clearance. • Continuously high levels of biomarkers reflecting lupus nephritis activity are risk factors of declining renal function.

Limited Reliability of the Spot Urine Protein/Creatinine Ratio in the Longitudinal Evaluation of Patients With Lupus Nephritis

Introduction

Cross-sectional studies document that the spot protein/creatinine ratio (PCR) is often an inaccurate estimate of proteinuria magnitude compared with the 24-hour PCR, which is the gold standard. However, the extent to which the inaccuracy of the spot PCR varies over time and between individuals has not previously been reported. We address these crucial questions using a unique database, an National Institutes of Health trial in which lupus nephritis (LN) patients (N = 103) provided spot PCR testing each month and 24-hour PCR testing every 3 months for up to 15 months after induction therapy.

Methods

A gold standard proteinuria trend line was constructed for each patient by joining the points that represented the serial 24-hour PCR values of the patient. The spot PCR values of the patient were then plotted in relationship to the 24-hour PCR trend line. Using our previous work, which estimated the 95% confidence intervals for the 24-hour PCR at specific levels, we determined in each patient whether the spot PCR values were "reliable," "problematic," or "unreliable." The sequential spot PCR of the patients deviated widely and often from the 24-hour PCR trend line, to the extent that, if the spot PCR results were used in real time for clinical decision-making, it was likely management errors would occur.

Results

Spot PCRs were reliable in 41%, problematic in 24%, and unreliable in 35% of patients. Those with unreliable spot PCRs could not be predicted and were more likely to respond poorly to treatment.

Conclusion

The spot PCR should not be used for management of LN, and perhaps, other glomerulopathies.

Combined utilization of untimed single urine of MCP-1 and TWEAK as a potential indicator for proteinuria in lupus nephritis: A case-control study

The aim of this study was to determine whether combined utilization of untimed single urine monocyte chemoattractant protein 1 (uMCP-1) and tumor necrosis factor (TNF)-like weak inducer of apoptosis (uTWEAK) could serve as a screening test for proteinuria in patients with lupus nephritis (LN).A case-control study that contained 39 biopsy-proven LN patients, 20 non-LN systemic lupus erythematosus (SLE) patients, and 10 healthy controls (HCs) were carried out. Correlations between uMCP-1, uTWEAK, and traditional clinical markers were analyzed by Spearman correlation test. Diagnostic values of uMCP-1, uTWEAK, and urine albumin/creatinine ratio (uACR) in the assessment of proteinuria were investigated by receiver operating characteristic (ROC) curves.Biopsy-proven LN patients showed higher levels of uMCP-1 and uTWEAK than non-LN patients. uMCP-1 and uTWEAK were elevated in renal active patients (rSLEDAI ≥4). Both uMCP-1 and uTWEAK showed significant correlation with patients' rSLEDAI, 24-hour urine proteinuria (24hr UP), and anti-double-stranded DNA (anti-dsDNA) antibodies. No correlations of these 2 biomarkers between cystatin C (Cys-C), creatinine (Cr), and blood urea nitrogen (BUN) were observed. An algorithm combining the moderate sensitivity of uMCP-1 and high specificity of uTWEAK displayed great specificity and sensitivity for proteinuria screening.Both uMCP-1 and uTWEAK were positively correlated with the impairments of LN, and the combined utility of untimed single uMCP-1 and uTWEAK might be used as potential predictors for proteinuria in LN.

A New Gender-Specific Formula to Estimate 24-Hour Urine Protein from Protein to Creatinine Ratio

<b><i>Background:</i></b> The quantification of proteinuria with the protein to creatinine ratio (PCR) is influenced by the excretion of creatinine, which, in turn, varies according to muscle mass and hence, to gender. <b><i>Aims:</i></b> To assess the difference between urine PCR and 24-hour urine proteinuria in men and women and to provide a formula to overcome bias caused by gender. <b><i>Methods:</i></b> Four hundred and forty four CKD patients were randomly divided into 2 groups: 70% were used to develop the models, while the remaining 30% were reserved to validate the formula. Epidemiological data were analyzed with chi-square and Student's t tests. Association between 24-hour proteinuria and PCR was studied with Spearman coefficient in men and women separately. Multivariate analysis was used to find variables predictive of disagreement between the 24-hour urine protein and the PCR. Equations to predict 24-hour proteinuria from PCR for men and women were plotted and validated. <b><i>Results:</i></b> Disagreement between 24-hour proteinuria and PCR was more pronounced in men (2.16 and 1.64 g in mean, respectively) than in women (2.00 and 2.06 g in mean, respectively). Age and gender were independent predictors of disagreement. Gender-specific equations for predicting 24-hour proteinuria were: males: 24-hour proteinuria = 1.3350*exp^0.9108*^ln(PCR); females: 24-hour proteinuria = 1.0068*exp^0.9030*^ln(PCR). <b><i>Conclusions:</i></b> Estimation of proteinuria with the PCR improves accuracy if gender-specific equations are used. Use of the PCR without correction for gender leads to the underestimation of proteinuria in men and overestimation in women.

Utility of untimed single urine protein/creatinine ratio as a substitute for 24-h proteinuria for assessment of proteinuria in systemic lupus erythematosus

Introduction

In this study, we determined: (1) the utility of an untimed sample of urine protein/creatinine ratio (PCR) as a screening test for proteinuria, (2) its ability to accurately measure proteinuria, and (3) cutoff values for PCR predicting protein content in a 24-h urine collection sample (24hP) of 0.5, 1.0, and 2.0 g/day.

Methods

Analysis was performed on data from a single lupus cohort (2008–2014). Proteinuria was measured in a 24hP and with PCR. On the basis of 24hP, samples were divided into 4 groups: group 1, <0.5 g/day; group 2, 0.5–0.99 g/day; group 3, 1–1.99 g/day; and group 4, ≥2 g/day. To determine the validity of PCR in screening for proteinuria, the Pearson correlation coefficient was determined for the urine samples with normal PCR (<0.05 g/mmol) and normal 24hP (<0.5 g/day). The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of PCR were calculated. To determine the ability of PCR to accurately measure the level of proteinuria, in addition to the correlation between 24hP and PCR, agreement was determined by intraclass correlation coefficient, concordance correlation coefficient, and Bland-Altman plot between 24hP/24hC and PCR. The best cutoffs for PCR predicting a 24hP of 0.5, 1.0, and 2.0 g/day were determined with the receiver operating characteristic curve.

Results

The correlation of the samples with normal PCR as well as 24hP (n = 552) was 0.29 (p < 0.0001). PCR sensitivity and specificity against 24hP were 91 % and 83 %, respectively. The PPV was 82.5 %, and the NPV was 91.4 %. The correlation for all samples (n = 1233) was high, but low to moderate for groups 1, 2, 3, and 4. The agreement for all samples was appropriate but poor for groups 1, 2, 3, and 4. PCR cutoffs for 24hP of 0.5, 1.0, and 2.0 g/day were 0.08, 0.16, and 0.35 g/mmol, respectively.

Conclusions

PCR can be used as a screening test for proteinuria, and the best cutoff value to predict a 24hP of 0.5 g/day is 0.08 g/mmol (800 mg/g). The accurate level of proteinuria should be measured by the gold standard test, 24hP.

Urinary protein/creatinine ratio weighted by estimated urinary creatinine improves the accuracy of predicting daily proteinuria

BACKGROUND

The spot urine protein/creatinine ratio (UPCR) is proposed to be a substitute for 24-hour urinary protein (24h-UP). This study is aimed to determine whether the predictive accuracy of 24h-UP using UPCR can be improved by simply multiplying estimated daily urine creatinine excretion (eUCr) and UPCR together.

METHODS

This study enrolled 120 participants to investigate the correlation between spot UPCR and 24h-UP. Three sets of spot urine samples were randomly collected throughout the day and night, along with the first morning void. UPCR was weighted by eUCr to investigate the improvement of accuracy in using spot urine samples to predict 24h-UP.

RESULTS

There were strong correlation and concordance between UPCR and 24h-UP irrespective of the time of spot urine sampling, and the correlation, concordance and agreement were improved after multiplying the UPCR value by the eUCr. Greater improvement was found in the subgroups with measured daily urine creatinine excretion ≤ 0.8 g/d and ≥ 1.2 g/d.

CONCLUSIONS

This investigation demonstrated that multiplying UPCR by eUCr can improve the accuracy of only using UPCR to predict 24h-UP.

Spot urine protein/creatinine ratio is unreliable estimate of 24 h proteinuria in lupus nephritis when the histological scores of activity index are higher

OBJECTIVES

The aim of this study was to evaluate the correlation and agreement of spot urine protein/creatinine (P/C) ratio with 24 h proteinuria in patients with lupus nephritis (LN) under different scores of activity index (AI).

METHODS

In total, 90 pairs of 24 h urine and spot urine samples from 90 patients with biopsy-proven LN were analyzed. The correlation and agreement between the two sample types were assessed by Pearson correlation and intra-class correlation coefficient (ICC) using mixed model for repeated measurements, respectively.

RESULTS AND CONCLUSIONS

Overall, 24 h proteinuria correlated strongly with the spot urine P/C ratio (r = 0.671, p < 0.001) with a good agreement (ICC = 0.656, 95% confidence interval (CI): 0.52-0.76). Subgroup analyses revealed that the correlation remained high in all groups (r = 0.825, p < 0.001; r = 0.567, p = 0.001; r = 0.686, p = 0.020), the agreement in group A (low AI) was good (ICC = 0.824, 95% CI: 0.70-0.89), but in group B (middle AI) and group C (high AI), the agreements were weak (ICC = 0.503, 95% CI: 0.19-0.72; ICC = 0.532, 95% CI: 0.06-0.84). Our work suggests that over the range of a higher AI, however, correlation was present but agreement was poor.

Evaluation of the URiSCAN super cassette ACR semiquantitative urine dipstick for microalbuminuria screening

BACKGROUND

Microalbuminuria tests are used as screening tools for diseases, such as diabetic nephropathy, cardiovascular disease, and hypertension. The purpose of this study was to evaluate the utility of a newly introduced semiquantitative urine dipstick, URiSCAN Super cassette ACR (URiSuper-ACR [where ACR is albumin/creatinine ratio]; YD Diagnostics Corp., Korea), as a screening tool for microalbuminuria.

METHODS

Albumin and creatinine levels in randomly selected spot urine samples of 1,040 patients were semiquantitatively measured using URiSuper-ACR. Results using URiSuper-ACR system were compared to measurements obtained by quantitative analyzer. We also calculated diagnostic sensitivity, specificity, precision, linearity, and categorical concordance rates for the diagnosis of microalbumiuria using this system. Furthermore, we performed interference tests using standard controls to evaluate possible influence of various factors.

RESULTS

URiSuper-ACR test showed 88.8% and 86.3% sensitivity and 90.1% and 93.8% specificity for albumin concentration and ACR, respectively. It also showed 91.1% and 92.6% positive predictive values and 87.6% and 88.5% negative predictive values, respectively. The concordance rate between URiSuper-ACR and quantitative method for albumin and creatinine concentration within the same category were 78.4% and 67.1%, respectively, and for the ±1 category were 98.8% and 99.5%, respectively. For ACR, an 80.0% concordance rate was seen within the same category. The within-run coefficients of variation (CVs) were 3.0∼15.4% and 5.2∼23.5% for albumin and creatinine, respectively, showing good linearity. In interference tests, no interference was observed except for cases with high specific gravity.

CONCLUSIONS

URiSuper-ACR showed good diagnostic performance for the detection of microalbuminuria and may be a useful screening test in clinical laboratories.

Random spot urine protein/creatinine ratio: a reliable method for monitoring lupus nephritis?

Background

Lupus nephritis (LN) is a common and severe manifestation of systemic lupus erythematosus (SLE) that can lead to end-stage renal disease. According to the Kidney Disease Outcomes Global Improving clinical Guidelines for Glomerulonephritis, spot urine protein/creatinine (P/C) ratio should be used for monitoring LN. However, some reports write that the random spot urine P/C ratio is unreliable in monitoring proteinuria in SLE glomerulonephritis patients. The aim of this study was to evaluate the agreement of these two assay methods.

Methods

The prospective observational study was performed. Fifty-three paired (total 106) spot and 24-h urine collections were evaluated. Statistical analysis: SPSS 20.0.

Results

Paired samples t-test did not reveal significant differences between the two-paired assay methods (spot P/C ratio versus 24-h proteinuria and 24-h P/C ratio) and a statistically significant correlation was observed between them: Pearson's coefficient of 0.847 (P < 0.001) and 0.863 (P < 0.001), respectively. However, after stratifying by degrees of proteinuria, a poor correlation was found in the range of <500 mg/day and only 26.6% of 24-h P/C ratio was explained by the spot P/C ratio. Adding to this, for proteinuria range between 500 and 1000 mg/day, there was no correlation (Pearson's −0.098; P > 0.05). In fact, only 1% of 24-h measurements could be explained by the spot P/C ratio.

Conclusions

Our study demonstrated a good correlation between 24-h proteinuria and random P/C ratio among patients with LN. However, this correlation was poor for proteinuria under 500 mg/day and did not exist in a range between 500 and 1000 mg/day. This finding is of greater importance because this range is quite common in patients with LN remission. Until further clarification, to the best of our knowledge, we maintain reluctant to completely substitute the 24-h collection by the P/C ratio especially when a renal flare is suspected, or before any change in therapy.

Differential diagnosis of glomerular disease: a systematic and inclusive approach

BACKGROUND

Glomerular disease is a complex and evolving topic. In evaluating a specific case it is not unusual for the clinician to ask: 'Am I missing something? Should I biopsy? When? Should I treat first, then biopsy?' This work, which is both evidence and experience based, is intended to address each of these concerns and many other issues relevant to the differential diagnosis of glomerular disease.

SUMMARY

The central approach is the use of diagnostic algorithms that are based on quantitative measures routinely obtained early in the course of the diagnostic evaluation. The algorithms are designed to be easy to navigate, systematic, and inclusive. Also provided is a detailed and prioritized list of recommended diagnostic testing, and the rationale for each test.

KEY MESSAGE

This work is intended to facilitate accurate diagnosis in the individual patient presenting with evidence of glomerular disease.

Diagnosis and treatment of lupus nephritis flares--an update

Relapses or flares of systemic lupus erythematosus (SLE) are frequent and observed in 27-66% of patients. SLE flares are defined as an increase in disease activity, in general, requiring alternative treatment or intensification of therapy. A renal flare is indicated by an increase in proteinuria and/or serum creatinine concentration, abnormal urine sediment or a reduction in creatinine clearance rate as a result of active disease. The morbidity associated with renal flares is derived from both the kidney damage due to lupus nephritis and treatment-related toxic effects. Current induction treatment protocols achieve remission in the majority of patients with lupus nephritis; however, few studies focus on treatment interventions for renal flares in these patients. The available data, however, suggest that remission can be induced again in a substantial percentage of patients experiencing a lupus nephritis flare. Lupus nephritis flares are independently associated with an increased risk of deterioration in renal function; prevention of renal flares might, therefore, also decrease long-term morbidity and mortality. Appropriate immunosuppressive maintenance therapy might lead to a decrease in the occurrence of renal and extrarenal flares in patients with SLE, and monitoring for the early detection and treatment of renal flares could improve their outcomes.

An approach to validating criteria for proteinuric flare in systemic lupus erythematosus glomerulonephritis

OBJECTIVE

Published criteria on the degree of proteinuria increase that defines a proteinuric flare in systemic lupus erythematosus (SLE) with glomerulonephritis (GN) vary widely, likely because they are not evidence based, but are largely based on expert opinion. Ideally, the threshold for proteinuric flare should be set sufficiently high that spontaneous variation in proteinuria does not likely explain the increase, but not so high that the patient needlessly experiences prolonged severe proteinuria before a flare is declared and therapy is increased. The present study was undertaken to develop an evidence-based approach to setting the threshold for proteinuric flare, based on quantifying the spontaneous variation in the urine protein:creatinine ratio in SLE GN patients who are not experiencing SLE flare.

METHODS

SLE GN patients (n = 71) in the Ohio SLE Study were tested at prespecified bimonthly intervals within windows of ±1 week. The median duration of followup was >44 months, and the rate of visit compliance was >90%. To assess spontaneous variation in the protein:creatinine ratio under no-flare conditions, we excluded protein:creatinine ratios measured within 4 months before or after renal flare.

RESULTS

Our findings showed that in the group of SLE GN patients with a mean no-flare protein:creatinine ratio of ≤0.5, the published flare thresholds are set well above the 99% confidence interval of the no-flare protein:creatinine ratio. The opposite was seen in the group with a mean no-flare protein:creatinine ratio of ≥1.0.

CONCLUSION

Current thresholds for defining proteinuric flare appear to be set either too high or too low. A randomized trial would be needed to test whether resetting the thresholds would result in faster remission, reduction in therapy, and decrease in the frequency of chronic kidney disease.

Urinary biomarkers in lupus nephritis

Renal involvement in patients with systemic lupus erythematosus in the form of severe lupus nephritis is associated with a significant burden of morbidity and mortality. Conventional laboratory biomarkers in current use have not been very successful in anticipating disease flares, predicting renal histology, or decreasing unwanted outcomes. Since early treatment is associated with improved clinical results, it is thus essential to identify new biomarkers with substantial predictive power to reduce the serious sequelae of this difficult to control lupus manifestation. Indeed, considerable efforts and progress have been made over the last few years in the search for novel biomarkers. Since urinary biomarkers are more easily obtainable with much less risk to the patient than repeat renal biopsies, and these may more accurately discern between renal disease and other organ manifestations than their serum counterparts, there has been tremendous interest in studying new candidate urine biomarkers. Below, we review several promising urinary biomarkers under investigation, including total proteinuria and microalbuminuria, urinary proteomic signatures, and the individual inflammatory mediators interleukin-6, vascular cell adhesion molecule-1, CXCL16, IP-10, and tumor necrosis factor-like weak inducer of apoptosis.

Relapse or worsening of nephrotic syndrome in idiopathic membranous nephropathy can occur even though the glomerular immune deposits have been eradicated

BACKGROUND

Relapse or worsening of nephrotic syndrome (NS) in idiopathic membranous nephropathy (IMN) is generally assumed to be due to recurrent disease. Here we document that often that may not be the case.

SUBJECTS AND METHODS

This is a prospective study of 7 consecutive IMN patients whose renal status improved, then worsened after completing a course of immunosuppressive therapy. Each underwent detailed testing and repeat kidney biopsy.

RESULTS

In 4 patients (group A), the biopsy showed recurrent IMN (fresh subepithelial deposits). Immunosuppressive therapy was begun. In the other 3 patients (group B), the biopsy showed that the deposits had been eradicated. However, the glomerular basement membrane (GBM) was thickened and vacuolated. Immunosuppressive therapy was withheld. Groups A and B were comparable except that group B had very high intakes of salt and protein, based on 24-hour urine testing. Reducing their high salt intake sharply lowered proteinuria to the subnephrotic range and serum creatinine stabilized.

CONCLUSION

This work is the first to demonstrate that relapse/worsening of NS can occur in IMN even though the GBM deposits have been eradicated. High salt and protein intake in combination with thickened and vacuolated GBM appears to be the mechanism.

Comparison of estimated protein output and urine protein: creatinine ratio in first and second voids with 24-hour urine protein

BACKGROUND

Current UK guidelines for the identification, management and referral of chronic kidney disease advise an early-morning urine sample for the albumin:creatinine ratio or the protein:creatinine ratio (PCR) in order to quantify proteinuria. Estimated protein output (EPO) is an alternative and possibly better method of quantifying proteinuria which takes lean weight into consideration.

METHODS

We carried out a single-centre study of 36 adult patients with proteinuric nephropathy over a period of 18 months. Urinary PCR and EPO estimates of 24-hour urine protein were compared with 24-hour urine collections by Bland-Altman analysis.

RESULTS

Average 24-hour urine protein was 1.6 g (range 0.2-5.1 g). Best agreement with 24-hour protein was for first-void EPO (limits of agreement 0.33-1.59) followed by a second-void EPO (0.40-1.76), then second-void PCR (0.40-2.08) and lastly first-void PCR (0.28-2.03). None of the differences between estimates of urine protein excretion and 24-hour urine protein were statistically significant. All estimates of protein output had wide confidence intervals confirming that spot urine samples, while simple and convenient to do, are imprecise measures of 24-hour urine protein excretion.

CONCLUSION

When estimating 24-hour urine protein from a spot urine sample, EPO may be marginally more accurate than PCR, and first-void urine samples slightly better than second-void urine samples, but a first- or second-void PCR will suffice in most instances.

A prospective study of protein excretion using short-interval timed urine collections in patients with lupus nephritis

The 24-h urine protein-to-creatinine ratio is the gold standard in evaluating proteinuria in lupus nephritis; however, the urine collection is inconvenient to the patient. Random spot urine protein-to-creatinine ratios, although convenient, have poor agreement with the 24-h ratios in these patients. Here, we sought to define a timed collection interval providing accurate and precise data and patient convenience. Urine from 41 patients, in 2 medical centers, with biopsy-proven lupus nephritis was collected at 6-h intervals for 24 h. The protein-to-creatinine ratio of each short collection was then compared with that of a 24-h collection made by combining the 6-h samples. A first morning void and spot urine samples were collected before and after the 24-h collection, respectively. There was significant diurnal variation with peak proteinuria at 6-12 h and nadir at 18-24 h. Each 6-h collection showed excellent correlation and concordance with the 24-h protein-to-creatinine ratio, but the 12-24-h interval had the best agreement. In contrast to the random spot urines, the first morning void also had excellent correlation and concordance, but underestimated the 24-h protein-to-creatinine ratio. Our study shows that a 12-h overnight urine collection is the best surrogate, with excellent agreement with the 24-h protein-to-creatinine ratio, and it is convenient for patients. There was little variability between centers, an important feature for clinical trials.

Random spot urine protein/creatinine ratio is unreliable for estimating 24-hour proteinuria in individual systemic lupus erythematosus nephritis patients

BACKGROUND

Recently the American Rheumatologic Association (ARA) recommended random spot urine protein/creatinine ratio (P/C) to monitor systemic lupus erythematosus (SLE) glomerulonephritis (GN). Shortly afterward, 2 works were published, designated Study 1 and Study 2, which are the only studies to test spot P/C in SLE GN. Here we evaluate Study 1 and Study 2, which came to different conclusions.

METHODS

Study 1 compared spot P/C to the P/C of intended 24-hour collections >50% complete, which reliably estimates 24-hour proteinuria. Study 2 compared spot P/C to the protein content of intended 24-hour collections >80% complete. To compare studies, Study 2 data were converted to P/C ratios.

RESULTS

Study 1 and Study 2 were found to be in agreement. Both showed that spot P/C and 24-hour P/C were highly correlated, but only when compared over the entire P/C range (0-8.0) (r = 0.842). Over the P/C range 0.5-3.0 (the most common P/C range encountered in SLE GN), correlation was present, but concordance was poor, rendering random P/C ratio unreliable.

CONCLUSIONS

Random spot P/C ratio is unreliable for detecting moderate proteinuria change. For example, random spot P/C would not reliably diagnose British Isles Lupus Assessment Group (BILAG) Category A or B proteinuric flares.

Beyond immunosuppression – challenges in the clinical management of lupus nephritis

Lupus nephritis remains the most common severe manifestation of SLE with increased risk of death and end-stage renal disease. Although, recent research has focused on the choice of immunosuppressive in its treatment, other factors, including the quality and delivery of healthcare, the management of glucocorticoids and co-morbidity are probably of more importance. There has been significant progress in induction regimes with the successful use of mycophenolate mofetil, low dose intravenous cyclophosphamide and development of sequential regimens whereby cyclophosphamide is followed by an alternative immunosuppressive. However, the attention on the day-to-day management of lupus nephritis in the clinic has merited less attention. In this article, we aim to address more widely the major issues which are encountered regularly in the long-term management of these patients. The overall goals are the reduction of mortality and preservation of renal function.

D-dimer level and the risk for thrombosis in systemic lupus erythematosus

BACKGROUND AND OBJECTIVES

Patients who have systemic lupus erythematosus (SLE) and manifest antiphospholipid antibodies (APA) are at increased risk for thrombosis; however, it is difficult to predict who will clot. This study tested the hypothesis that peak D-dimer level measured routinely during follow-up identifies whether a hypercoagulable state is developing and, therefore, the patient is at increased risk for thrombosis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

One hundred consecutive patients who had SLE with recurrent activity (71% renal SLE) and were evaluated for or enrolled in the Ohio SLE Study were studied. D-dimer testing was done annually and usually at SLE flare or other serious illness. When D-dimer was elevated, evaluation for thrombosis (large vessel, small vessel, or Libman-Sacks) was undertaken. Mean follow-up was 37.5 +/- 15 SD months.

RESULTS

Of those with peak D-dimer <0.5 microg/ml (n = 46), 0% thrombosed, 33% had APA. Of those with peak D-dimer 0.5 to 2.0 microg/ml (n = 19), 6% thrombosed, 44% had APA. Of those with peak D-dimer >2.0 microg/ml (n = 36), 42% thrombosed, 76% had APA. The most common causes of elevated D-dimer in the absence of demonstrable thrombosis were SLE flare and systemic infection. D-dimer levels were usually elevated for several months before thrombosis.

CONCLUSIONS

Patients with SLE and normal D-dimer levels are at low risk for thrombosis, irrespective of APA status. Those with persistent unexplained elevated D-dimer levels, particularly when >2.0 microg/ml, are at high risk for thrombosis.

Relationship between albuminuria and total proteinuria in systemic lupus erythematosus nephritis: diagnostic and therapeutic implications

BACKGROUND AND OBJECTIVES

Albuminuria is regarded a sensitive measure of progression of glomerular disease. This study was undertaken in patients who had systemic lupus erythematosus glomerulonephritis (n = 57) and were followed in the Ohio SLE Study to determine whether measuring albuminuria offered clinical advantages over that of total proteinuria.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Twenty-four-hour urine collections (n = 127) were obtained at baseline and annually for measurement of microalbumin, total protein, and creatinine.

RESULTS

There was a strong linear relationship between microalbumin-creatinine and protein-creatinine ratios over the entire range of protein-creatinine ratios; however, in the protein-creatinine ratio range 0.0 to 0.3, as the protein-creatinine ratio increased, the microalbumin-protein ratio increased much more than the protein-creatinine ratio. Also, the greater the protein-creatinine ratio, the greater was the evidence for nonselective proteinuria (protein-creatinine ratio--microalbumin-creatinine ratio).

CONCLUSIONS

For the diagnosis of proteinuria renal flare, measuring albuminuria offers no advantage over measuring total proteinuria because changes in protein-creatinine and microalbumin-creatinine ratios are highly correlated over the designated ranges for systemic lupus erythematosus glomerulonephritis proteinuric flares. In those with normal-range proteinuria, subsequent changes in microalbumin-protein ratio might be a better forecaster of renal flare than changes in protein-creatinine or microalbumin-creatinine ratio. High protein-creatinine ratios are associated with evidence of nonselective proteinuria, which may increase the nephrotoxicity of proteinuria. Thus, using high-threshold criteria for systemic lupus erythematosus flare (allowing greater proteinuria increase before flare is declared) may expose the kidney to greater nephrotoxicity than using the low-threshold criteria for systemic lupus erythematosus flare.