Spot Urine Protein Measurements: Are these Accurate in Kidney Transplant Recipients?

Estimation of 24-h Urine Protein Excretion Using Urine Albumin-to-Creatinine Ratio from an In-Hospital Population

BACKGROUND There is little information available on quantitative description of the relationship between urine albumin-to-creatinine ratio (ACR) and 24-h urine protein excretion (24-h UPE). Here, we developed a calculation tool for 24-h UPE using the urine ACR and limited information on the request form. MATERIAL AND METHODS This was a retrospective and observational study. All individuals with same-day urine ACR and 24-h UPE tests in Sichuan Provincial People's Hospital from September 1, 2018 to December 31, 2019 were enrolled. Correlation and agreement between urine ACR and 24-h UPE were evaluated using correlation analysis and an intraclass correlation coefficient, respectively. The Durbin-Watson test and ANOVA were used to assess the performance of the calculation tool, and reliability of the prediction equation was evaluated in the validation group using residual error analysis. RESULTS A total of 906 participants were enrolled, including 639 participants in the development group and 267 in the validation group. Natural logarithm transformation was applied to remove skewness. Natural logarithm-transformed urine ACR correlated well with natural-logarithm-transformed 24-h UPE (Pearson coefficient=0.908; P<0.001) and the agreement was consistently good (overall ICC=0.938; 95% CI: 0.928-0.947; P<0.001). The multivariable regression model had good performance (R²=0.864) and high accuracy, demonstrated by results of residual error analysis. CONCLUSIONS We provide a practical calculation tool to estimate total protein excretion using urine ACR and readily accessible variables. However, 24-h UPE is still mandatory when proteinuria is over 10 g/day or when most proteinuria may not be of glomerular origin.

Spot Urine Protein Excretion in the First Year Following Kidney Transplantation Associates With Allograft Rejection Phenotype at 1-Year Surveillance Biopsies: An Observational National-Cohort Study

Introduction: Urine protein excretion is routinely measured to assess kidney allograft injury, but the diagnostic value of this measurement for kidney transplant pathology remains unclear. Here we investigated whether spot urine protein excretion in the first year following transplantation associates with allograft rejection phenotype at 1-year surveillance biopsies and de-novo occurrence of donor-specific antibodies (DSA). Patients and Methods: This prospective, observational national-cohort study included 139 non-sensitized patients who received a deceased donor kidney transplant between December 2014 and 2018. All patients received basiliximab induction and tacrolimus-based immunosuppression. Estimated protein excretion rate (ePER) was calculated monthly from spot urine protein-to-creatinine ratios. At 1-year, all recipients underwent surveillance graft biopsy and were screened for de-novo DSA. Screening-positive sera were subjected to single antigen bead (SAB) testing. The occurrence of de-novo DSA was determined based on SAB reactivity patterns using a mean fluorescence intensity threshold >1,000. Results: Among the 139 study patients, 27 patients (19%) had histologic evidence of T cell-mediated rejection (TCMR), and 9 patients (7%) had histologic evidence of antibody-mediated rejection (AMR) at 1-year surveillance biopsy. One year after transplant, 19 patients (14%) developed de-novo DSA. Compared with patients without rejection and no de-novo DSA, mixed-effects linear regression analysis showed a significant difference in slope of ePER during the first year in patients with AMR and de-novo DSA at 1-year (46, 95% CI 25-68 mg/day/1.73 m² per month and 34, 95% CI 20-49 mg/day/1.73 m² per month, respectively). Patients with vascular TCMR also showed a significant difference in ePER slope over time compared with patients with non-rejection findings (31, 95% CI 9-52 mg/day/1.73 m² per month). The discriminatory power of ePER for intragraft rejection processes was better in patients with AMR (AUC 0.95, 95% CI 0.90-0.99; P < 0.001) than in those with TCMR (AUC 0.68, 95% CI 0.59-0.79; P = 0.002), with 89% sensitivity and 93% specificity for proteinuria >550 mg/day/1.73m². Conclusions: An increase in ePER in the first year following kidney transplantation associates with AMR, vascular TCMR and de-novo DSA at 1-year and may be used as a non-invasive clinical marker of intragraft endothelial cell injury.

First and second morning spot urine protein measurements for the assessment of proteinuria: a diagnostic accuracy study in kidney transplant recipients

BACKGROUND

Quantification of proteinuria in kidney transplant recipients is important for diagnostic and prognostic purposes. Apart from correlation tests, there have been few evaluations of spot urine protein measurements in kidney transplantation.

METHODS

In this cross-sectional study involving 151 transplanted patients, we investigated measures of agreement (bias and accuracy) between the estimated protein excretion rate (ePER), determined from the protein-to-creatinine ratio in the first and second morning urine, and 24-h proteinuria and studied their performance at different levels of proteinuria. Measures of agreement were reanalyzed in relation to allograft histology in 76 patients with kidney biopsies performed for cause before enrolment in the study.

RESULTS

For ePER in the first morning urine, percent bias ranged from 1 to 28% and accuracy (within 30% of 24-h collection) ranged from 56 to 73%. For the second morning urine, percent bias ranged from 2 to 11%, and accuracy ranged from 71 to 78%. The accuracy of ePER (within 30%) in first and second morning urine progressively increased from 56 and 71% for low-grade proteinuria (150-299 mg/day) to 60 and 74% for moderate proteinuria (300-999 mg/day), and to 73 and 78% for high-grade proteinuria (≥1000 mg/day). Measures of agreement were similar across histologic phenotypes of allograft injury.

CONCLUSIONS

The ability of ePER to accurately predict 24-h proteinuria in kidney transplant recipients is modest. However, accuracy improves with an increase in proteinuria. Given the similar accuracy of ePER measurements in first and second morning urine, second morning urine can be used to monitor protein excretion.

24-Hour Proteinuria Versus Spot Protein-Creatinine Ratio for Kidney Transplant Management in Clinical Practice

BACKGROUND

24-hour proteinuria (24h-P) has been the most widespread test for clinical follow-up of proteinuria after kidney transplantation (KT), but urine collection is often not properly collected. Spot protein-creatinine ratio (P/Cr) has become the alternative to 24h-P for proteinuria evaluation in many KT units. However, its reliability, equivalence to 24h-P, and prognostic value regarding allograft outcome remain unknown. Therefore, the aim of this study was to evaluate the correlation and agreement between both methods for assessing proteinuria and to analyze which of them is a better predictor of graft survival.

METHODS

We collected proteinuria measurements from KT patients in our center. 24h-P was adjusted for body surface area. Pearson correlation test and the Bland-Altman method were used to analyze correlation and agreement. Survival analysis was performed with the use of the Kaplan-Meier method and multivariate Cox proportional hazard model.

RESULTS

A total of 8,549 urine samples were analyzed from 472 patients in whom 24h-P and P/Cr were simultaneously measured. A significant correlation was observed between 24h-P and P/Cr (r = .76; P < .001); however, the agreement between methods showed that P/Cr overestimated proteinuria compared with 24h-P, particularly when the latter was >1 g/24 h. The Cox regression multivariate model showed an increased risk of graft loss associated with proteinuria when assessed by either 24h-P (hazard ratio [HR] 6.53, 95% confidence interval [CI] 2.49-17.1) or P/Cr (HR 3.34, 95% CI 1.04-10.7).

CONCLUSIONS

P/Cr is an method interchangeable with 24h-P for detecting proteinuria after KT. When proteinuria increases, the P/Cr overestimates 24h-P, even though it also has a significant and similar prognostic value for predicting graft survival.

Decrease in 1-year Kidney Graft Size Predicts Inferior Outcomes After Deceased Donor Kidney Transplantation

BACKGROUND

Longest bipolar length of the kidney graft is routinely measured for ultrasonographic assessment of graft size (GS), although the value of the graft length remains unclear.

METHODS

In a single-center, observational study involving 319 deceased-donor kidney transplant recipients, we assessed variations in absolute and adjusted GS (corrected for body surface area) between 1 and 12 months after transplantation ([INCREMENT]GS1m→12m). We tested whether variations in GS during the first year were predictive of the composite outcome of a reduction of 50% or more in the estimated glomerular filtration rate or end-stage graft failure.

RESULTS

At 1 year after transplantation, 121 patients (38%) had a decrease in GS ([INCREMENT]GS1m→12m <0), and 198 patients (62%) had an increase in GS ([INCREMENT]GS1m→12m ≥0). After a median follow-up of 53 months, 41 patients with a decrease in GS reached the composite outcome as compared with 12 patients with an increase in GS (34% and 6%, respectively; P < 0.001). Areas under the receiver operating characteristics curves of absolute and adjusted [INCREMENT]GS1m→12m for composite outcome were 0.81 (95% confidence interval [95% CI], 0.74-0.88) and 0.78 (95% CI, 0.70-0.86), respectively. In multivariate analysis, the risk of the composite outcome was significantly higher among patients with a decrease in GS during the first year after transplantation (hazard ratio, 4.55; 95% CI, 2.35-8.81; P < 0.001).

CONCLUSIONS

A decrease in kidney GS during the first year after transplantation, as compared with an increase in GS, is a powerful predictor of subsequent graft dysfunction or end-stage graft failure.

Subclinical hypothyroidism and diabetic nephropathy in Iranian patients with type 2 diabetes

PURPOSE

Association of subclinical hypothyroidism with type 2 diabetes and its complications has been previously documented. These reports were, however, inconclusive and mainly gathered from Chinese and East Asian populations. In this study, we aimed to determine the prevalence of subclinical hypothyroidism and its relationship with diabetic nephropathy in Iranian individuals with type 2 diabetes, drawn from a white Middle Eastern population with an increasing prevalence of diabetes.

METHODS

In this cross-sectional study, 255 Iranian participants with type 2 diabetes and without history of thyroid disorders were included. Patients with TSH > 4.2 mIU/L and normal T4 were classified as having subclinical hypothyroidism. Diabetic nephropathy was diagnosed based on abnormal 24-h urinary albumin or protein measurements (24-h urinary albumin ≥30 mg/day or 24-h urinary protein ≥150 mg/day). Multivariate logistic regression was employed to obtain the OR for the relationship between subclinical hypothyroidism and diabetic nephropathy.

RESULTS

We found that subclinical hypothyroidism and diabetic nephropathy were as prevalent as 18.1 and 41.2 %, respectively, among the participants. We also found that subclinical hypothyroidism was independently associated with higher rates of diabetic nephropathy, after multivariable adjustment (OR [95 % CI] 3.23 [1.42-7.37], p = 0.005).

CONCLUSIONS

We found that the prevalence of subclinical hypothyroidism in Iranian diabetic population was among the highest rates reported to date. Our data supported the independent association of subclinical hypothyroidism with diabetic nephropathy, calling for further investigations to evaluate their longitudinal associations.

Utilizing Estimated Creatinine Excretion to Improve the Performance of Spot Urine Samples for the Determination of Proteinuria in Kidney Transplant Recipients

BACKGROUND

Agreement between spot and 24-hour urine protein measurements is poor in kidney transplant recipients. We investigated whether using formulae to estimate creatinine excretion rate (eCER), rather than assuming a standard creatinine excretion rate, would improve the estimation of proteinuria from spot urine samples in kidney transplant recipients.

METHODS

We measured 24 hour urine protein and albumin and spot albumin:creatinine (ACR) and spot protein:creatinine (PCR) in 181 Kidney transplant recipients." We utilized 6 different published formulae (Fotheringham, CKD-EPI, Cockcroft-Gault, Walser, Goldwasser and Rule) to estimate eCER and from it calculated estimated albumin and protein excretion rate (eAER and ePER). Bias, precision and accuracy (within 15%, 30% and 50%) of ACR, PCR, eAER, ePER were compared to 24-hour urine protein and albumin.

RESULTS

ACR and PCR significantly underestimated 24-hour albumin and protein excretion (ACR Bias (IQR), -5.9 mg/day; p< 0.01; PCR Bias, (IQR), -35.2 mg/day; p<0.01). None of the formulae used to calculate eAER or ePER had a bias that was significantly different from the 24-hour collection (eAER and ePER bias: Fotheringham -0.3 and 7.2, CKD-EPI 0.3 and 13.5, Cockcroft-Gault -3.2 and -13.9, Walser -1.7 and 3.1, Goldwasser -1.3 and -0.5, Rule -0.6 and 4.2 mg/day respectively. The accuracy for ACR and PCR were lower (within 30% being 38% and 43% respectively) than the corresponding values estimated by utilizing eCER (for eAER 46% to 49% and ePER 46-54%).

CONCLUSION

Utilizing estimated creatinine excretion to calculate eAER and ePER improves the estimation of 24-hour albuminuria/proteinuria with spot urine samples in kidney transplant recipients.