Impact of pancreas transplantation alone on kidney function: A multicenter clinical cohort study.

Pancreas transplantation alone (PTA) is a ß cell replacement option for selected patients with type 1 diabetes mellitus; concerns have been raised regarding deterioration in kidney function (KF) after PTA. This retrospective multicenter study assessed actual impact of transplantation and immunosuppression on KF in PTA recipients at three Transplant Centers. The primary composite endpoint 10 years after PTA was >50% eGFR decline, eGFR < 30 mL/min/1.73 m2 , and/or receiving a kidney transplant (KT). Overall, 822 PTA recipients met eligibility. Median baseline and 10-year eGFR (mL/min/1.73 m2 ) were 76.3 (58.1-100.8) and 51.3 (35.3-65.9), respectively. Primary composite endpoint occurred in 98 patients (53.5%) with 45 experiencing a >50% decrease in eGFR by 10 years post-transplant, 38 eGFR < 30 mL/min/1.73 m2 and 49 requiring KT. KF declined most significantly within 6 months post-PTA, more often in females and patients with better preserved GFR up to 5 years with 11.6% kidney failure at 10 years. Patient survival and death-censored graft survival were both 68% at 10 years with overall graft thrombosis rate 8%. KF declined initially after PTA but stabilized with further slow progression. In conclusion, prospective intervention studies are needed to test renal sparing interventions while gathering more granular data.

Race-free estimated glomerular filtration rate equation in kidney transplant recipients: development and validation study.

OBJECTIVE: To compare the performance of a newly developed race-free kidney recipient specific glomerular filtration rate (GFR) equation with the three current main equations for measuring GFR in kidney transplant recipients. DESIGN: Development and validation study SETTING: 17 cohorts in Europe, the United States, and Australia (14 transplant centres, three clinical trials). PARTICIPANTS: 15 489 adults (3622 in development cohort (Necker, Saint Louis, and Toulouse hospitals, France), 11 867 in multiple external validation cohorts) who received kidney transplants between 1 January 2000 and 1 January 2021. MAIN OUTCOME MEASURE: The main outcome measure was GFR, measured according to local practice. Performance of the GFR equations was assessed using P30 (proportion of estimated GFR (eGFR) within 30% of measured GFR (mGFR)) and correct classification (agreement between eGFR and mGFR according to GFR stages). The race-free equation, based on creatinine level, age, and sex, was developed using additive and multiplicative linear regressions, and its performance was compared with the three current main GFR equations: Modification of Diet in Renal Disease (MDRD) equation, Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) 2009 equation, and race-free CKD-EPI 2021 equation. RESULTS: The study included 15 489 participants, with 50 464 mGFR and eGFR values. The mean GFR was 53.18 mL/min/1.73m2 (SD 17.23) in the development cohort and 55.90 mL/min/1.73m2 (19.69) in the external validation cohorts. Among the current GFR equations, the race-free CKD-EPI 2021 equation showed the lowest performance compared with the MDRD and CKD-EPI 2009 equations. When race was included in the kidney recipient specific GFR equation, performance did not increase. The race-free kidney recipient specific GFR equation showed significantly improved performance compared with the race-free CKD-EPI 2021 equation and performed well in the external validation cohorts (P30 ranging from 73.0% to 91.3%). The race-free kidney recipient specific GFR equation performed well in several subpopulations of kidney transplant recipients stratified by race (P30 73.0-91.3%), sex (72.7-91.4%), age (70.3-92.0%), body mass index (64.5-100%), donor type (58.5-92.9%), donor age (68.3-94.3%), treatment (78.5-85.2%), creatinine level (72.8-91.3%), GFR measurement method (73.0-91.3%), and timing of GFR measurement post-transplant (72.9-95.5%). An online application was developed that estimates GFR based on recipient's creatinine level, age, and sex (https://transplant-prediction-system.shinyapps.io/eGFR_equation_KTX/). CONCLUSION: A new race-free kidney recipient specific GFR equation was developed and validated using multiple, large, international cohorts of kidney transplant recipients. The equation showed high accuracy and outperformed the race-free CKD-EPI 2021 equation that was developed in individuals with native kidneys. TRIAL REGISTRATION: ClinicalTrials.gov NCT05229939.

Clinical Impact of the Refit CKD-EPI 2021 Creatinine-Based eGFR Equation.

BACKGROUND: The National Kidney Foundation recently endorsed the refit Chronic Kidney Disease Collaboration (CKD-EPI) equation for estimated glomerular filtration rate (eGFR) using creatinine, age and sex [2021 eGFRCr(AS)] without a coefficient for race. We evaluated the impact of adopting the 2021 eGFRCr(AS) equation or a variation of the 2009 CKD-EPI eGFR equation without race [2009 CKD-EPI eGFRCr(ASR-NB)] compared to the original CKD-EPI eGFR [2009 eGFRCr(ASR)]. METHODS: The studied population included patients with a clinically ordered iothalamate clearance (n = 33 889). Bias was assessed as the difference between measured and estimated GFR, P30 was defined as the percentage of estimates within 30% of measured GFR, and concordance was determined according to relevant clinical thresholds. RESULTS: Among Black patients, the median bias for 2009 eGFRCr(ASR), 2009 eGFRCr(ASR-NB), and 2021 eGFRCr(AS) was -1.32 mL min-1 (1.73 m2)-1 (95CI -2.46 to -0.26), -8.81 mL min-1 (1.73 m2)-1 (95CI -9.93 to -7.58), and -6.08 mL min-1 (1.73 m2)-1 (95CI -7.18 to -4.92), respectively. The median bias among non-Black patients was -0.15 m min-1 (1.73 m2)-1 (95CI -0.84 to -0.08) for 2021 eGFRcr(AS) compared to -3.09 mL min-1 (1.73 m2)-1 (95CI -3.17 to -3.03) for the 2009 eGFRCr(ASR). P30 and concordance were not significantly different in either racial group. The net reclassification improvement at a measured GFR <20 mL min-1 (1.73 m2)-1 was 6.4% (95CI 0.36 to 12.4) for Black patients and -5.1% (95CI -6.0 to -4.1) for non-Black patients using the 2021 eGFRCr(AS) equation. CONCLUSIONS: Overall, the change in reported eGFR was minimal. However, these changes led to significant reclassification improvements at lower eGFR, which will indirectly improve equitable access to CKD resources.

Cystatin C Predicts Renal Recovery Earlier Than Creatinine Among Patients With Acute Kidney Injury.

INTRODUCTION: Serum cystatin C increases earlier than creatinine during acute kidney injury. However, whether cystatin C decreases earlier during recovery is unknown. This retrospective study aimed to determine the temporal trend between creatinine and cystatin C in acute kidney injury. METHODS: We identified hospitalized patients with nonoliguric acute kidney injury who had serial creatinine and cystatin C values measured between May 2015 and May 2016. Demographic and laboratory data, causes of acute kidney injury, and relevant comorbidity data were collected through chart review. RESULTS: For the 63 identified patients, mean (SD) age was 58.7 (13.9) years; male sex, 62%; white race/ethnicity, 95%. Baseline median (range) creatinine was 1.1 (0.5-3.0) mg/dl; 13% were kidney transplant recipients and 37% received corticosteroids. Comorbidities included malignancy (38%), diabetes mellitus (33%), heart failure (19%), and thyroid disorder (16%). The cause of kidney injury was acute tubular necrosis in 71%, 61% had acute kidney injury stage III, and 33% required dialysis. Cystatin C began to decrease before creatinine in 68% of patients: 1 day earlier, 46%; 2 days earlier, 16%; and 3 days earlier, 6%. In 24% of cases, both began decreasing on the same day; in only 8%, cystatin C decreased after creatinine. Overall, cystatin C mean (95% confidence interval) decrease was 0.92 (0.65-1.18) days before creatinine (P < 0.001). CONCLUSION: In summary, cystatin C decreases before creatinine in most hospitalized patients with acute kidney injury. If confirmed in large prospective studies, these findings may have important management implications, possibly shortening hospital stay and reducing costs.

Renal hemodynamic effects of the HMG-CoA reductase inhibitors in autosomal dominant polycystic kidney disease.

BACKGROUND: To determine the effect of statins on renal hemodynamics in normal volunteers and those with autosomal dominant polycystic kidney disease either with mild or moderate renal dysfunction. METHODS: Thirty-two study subjects were enrolled in this study: 11 normal volunteers, 11 study subjects with autosomal dominant polycystic kidney disease (ADPKD) and mild kidney disease and 10 study subjects with ADPKD and moderate kidney disease. Subjects in each group received simvastatin 40 mg once daily for a period of 4 weeks. Renal blood flow was measured based on para-amino-hippurate (PAH) clearance and with the use of a magnetic resonance (MR) scanner at the beginning and following 4 weeks of therapy with statins. RESULTS: At the end of the study, except for the lipid profile, which was significantly lower in all groups, other laboratory results showed no change. Four weeks of therapy with simvastatin resulted in no change in serum creatinine, 24-h urinary protein, sodium, iothalamate clearance, PAH clearance or renal blood flow as measured by MRI or based on PAH clearance. CONCLUSIONS: Four weeks of therapy with simvastatin did not change renal blood flow in the study subjects with ADPKD with mild-to-moderate renal dysfunction or in healthy volunteers. CLINICAL TRIAL REGISTRATION NUMBER: NCT02511418.

Discordance Between Iothalamate and Iohexol Urinary Clearances.

BACKGROUND: Iothalamate and iohexol are contrast agents that have supplanted inulin for the measurement of glomerular filtration rate (GFR) in clinical practice. Previous studies have noted possible differences in renal handling of these 2 agents, but clarity about the differences has been lacking. STUDY DESIGN: Study of diagnostic test accuracy. SETTING & PARTICIPANTS: 150 participants with a wide range of GFRs were studied in an outpatient clinical laboratory facility. INDEX TESTS: Simultaneous urinary clearances of iothalamate, iohexol, and creatinine. REFERENCE TEST: None. OUTCOME: Relative differences between the urinary clearances. Iohexol and iothalamate in plasma and urine were assayed concurrently by a novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay. RESULTS: Mean iohexol, iothalamate, and creatinine clearances were 52±28 (SD), 60±34, and 74±40 mL/min/1.73 m(2), respectively. The proportional bias of iohexol to iothalamate urinary clearance was 0.85 (95% CI, 0.83-0.88) and was proportional across the GFR range. The mean proportional bias of iohexol clearance compared with creatinine clearance is 1.27 (95% CI, 1.20-1.34), whereas that of iothalamate clearance compared with creatinine clearance is 1.09 (95% CI, 1.03-1.15). LIMITATIONS: Lack of reference standard. CONCLUSIONS: This study reveals a significant and consistent difference between urinary clearances of iothalamate and iohexol. Comparison of studies reporting renal clearance measurements using iohexol versus iothalamate must account for this observed bias.

Urinalysis is more specific and urinary neutrophil gelatinase-associated lipocalin is more sensitive for early detection of acute kidney injury.

BACKGROUND: Neutrophil gelatinase-associated lipocalin (NGAL) protein is a promising biomarker to detect acute kidney injury (AKI). Earlier detection of AKI could facilitate evaluation of novel therapeutic strategies. METHODS: Random and 24-h urine samples were prospectively obtained from 125 normal volunteers for analytic validation of a urinary enzyme-linked immunosorbent assay for NGAL. For clinical validation of the test, urine from 363 emergency department patients admitted to the hospital was obtained for NGAL enzyme-linked immunosorbent assay and urinalysis and AKI was determined by the use of Acute Kidney Injury Network (AKIN) criteria. RESULTS: NGAL was stable in urine for 7 days when ambient, 4 °C or frozen (-20 or -70 °C). The assay was linear between 0.24 and 10,000 ng/mL with a limit of quantitation of 0.24 ng/mL. Intra- and inter-assay precision were excellent (coefficient of variation <5%); however, urinary white blood cells were associated with increased NGAL levels. The 95th percentile reference value for NGAL in females is ≤ 65.0 and ≤ 23.4 ng/mL in males. Urinary NGAL levels increased with AKI stage but had only fair sensitivity (65%) and specificity (65%) to differentiate no AKI versus Stages 1, 2 or 3 (area under the curve 0.70). Urinalysis with microscopy was very specific (91%) but not very sensitive (22%) with an area under the curve of 0.57. CONCLUSIONS: NGAL can be reliably measured in clinical urine samples, although pyuria is an important potential confounder. In our cohort, increased urinary NGAL was associated with AKI by the AKIN criteria; however, the sensitivity and specificity were only fair, in part because patients with pre-renal causes are not excluded by AKIN criteria. Conversely, findings on microscopic urinalysis are very specific for AKI.

Identification and characterization of kidney transplants with good glomerular filtration rate at 1 year but subsequent progressive loss of renal function.

BACKGROUND: After the first year after kidney transplantation, 3% to 5% of grafts fail each year but detailed studies of how grafts progress to failure are lacking. This study aimed to analyze the functional stability of kidney transplants between 1 and 5 years after transplantation and to identify initially well-functioning grafts with progressive decline in allograft function. METHODS: The study included 788 adult conventional kidney transplants performed at the Mayo Clinic Rochester between January 2000 and December 2005 with a minimum graft survival and follow-up of 2.6 years. The modification of diet in renal disease equation for estimating glomerular filtration rate (eGFR(MDRD)) was used to calculate the slope of renal function over time using all available serum creatinine values between 1 and 5 years after transplantation. RESULTS: Most transplants demonstrated good function (eGFR(MDRD) ≥40 mL/min) at 1 year with positive eGFR(MDRD) slope between 1 and 5 years after transplantation. However, a subset of grafts with 1-year eGFR(MDRD) ≥40 mL/min exhibited strongly negative eGFR(MDRD) slope between 1 and 5 years suggestive of progressive loss of graft function. Forty-one percent of this subset reached graft failure during follow-up, accounting for 69% of allograft failures occurring after 2.5 years after transplantation. This pattern of progressive decline in estimated glomerular filtration rate despite good early function was associated with but not fully attributable to factors suggestive of enhanced antidonor immunity. CONCLUSIONS: Longitudinal analysis of serial estimated glomerular filtration ratemeasurements identifies initially well-functioning kidney transplants at high risk for subsequent graft loss. For this subset, further studies are needed to identify modifiable causes of functional decline.

Analytic and clinical validation of a standardized cystatin C particle enhanced turbidimetric assay (PETIA) to estimate glomerular filtration rate.

BACKGROUND: Cystatin C is an alternative biomarker for assessing glomerular filtration rate (GFR), yet lack of standardization could hinder its widespread use. In this study we analytically and clinically validated a newer cystatin C particle-enhanced turbidimetric assay (PETIA) traceable to a certified reference material and compared it to the more commonly used particle-enhanced nephelometric assay (PENIA). METHODS: Samples from four patient cohorts at the Mayo Clinic were studied: 1) clinical convenience samples (n=50); 2) samples from patients undergoing iothalamate urinary clearance testing for clinical indications (n=101); 3) volunteers without kidney disease (n=292); 4) samples from 1999-2000 with previous cystatin C measurements. RESULTS: The cystatin C PETIA was analytically robust between 0.15 mg/L and 8.36 mg/L. PETIA cystatin C values were 27.5% higher than PENIA results. Furthermore, PENIA results were 12.9% lower in 2010 than in 2000. PETIA cystatin C values and existing equations performed reasonably well to estimate GFR with an overall -7.4% bias for all patients analyzed. Age and gender specific reference intervals were established for the PETIA cystatin C. CONCLUSIONS: Cystatin C can be precisely measured by PETIA traceable to the international reference material, ERM-DA471/IFCC, using a routine chemistry autoanalyzer. There are important biases between this assay and the widely employed Siemens PENIA. This study highlights the importance of assay standardization if cystatin C is to be widely used to estimate GFR.

Relative performance of the MDRD and CKD-EPI equations for estimating glomerular filtration rate among patients with varied clinical presentations.

BACKGROUND: The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation was developed using both CKD and non-CKD patients to potentially replace the Modification of Diet in Renal Disease (MDRD) equation that was derived with only CKD patients. The objective of our study was to compare the accuracy of the MDRD and CKD-EPI equations for estimating GFR in a large group of patients having GFR measurements for diverse clinical indications. DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS: A cross-sectional study was conducted of patients who underwent renal function assessment for clinical purposes by simultaneous measurements of serum creatinine and estimation of GFR using the MDRD and CKD-EPI equations and renal clearance of iothalamate (n = 5238). RESULTS: Bias compared with measured GFR (mGFR) varied for each equation depending on clinical presentation. The CKD-EPI equation demonstrated less bias than the MDRD equation in potential kidney donors (-8% versus -18%) and postnephrectomy donors (-7% versus -15%). However, the CKD-EPI equation was slightly more biased than the MDRD equation in native CKD patients (6% versus 3%), kidney recipients (8% versus 1%), and other organ recipients (9% versus 3%). Among potential kidney donors, the CKD-EPI equation had higher specificity than the MDRD equation for detecting an mGFR <60 ml/min per 1.73 m(2) (98% versus 94%) but lower sensitivity (50% versus 70%). CONCLUSIONS: Clinical presentation influences the estimation of GFR from serum creatinine, and neither the CKD-EPI nor MDRD equation account for this. Use of the CKD-EPI equation misclassifies fewer low-risk patients as having reduced mGFR, although it is also less sensitive for detecting mGFR below specific threshold values used to define CKD stages.

The effect of coronary angiography on renal function in preemptive renal transplant candidates.

BACKGROUND: Increasing numbers of patients undergo preemptive renal transplantation. Obtaining cardiac catheterizations prior to transplantation to screen for coronary artery disease is controversial because of the perceived risk of inducing contrast nephropathy and the need for dialysis in patients with marginal renal function. We sought to examine the true impact of cardiac catheterization on time to dialysis in a cohort of preemptive renal transplant candidates. METHODS: From a cohort of 376 transplant candidates evaluated preemptively at our program between 2/2001 and 4/2005, 34 patients had positive dobutamine stress echocardiograms. We reviewed the subsequent need for dialysis in these patients. RESULTS: Among candidates undergoing angiography, 8.7% required dialysis within 14 d of contrast administration and 26% eventually needed dialysis prior to transplantation at 5.3 ± 3.7 months after their pre-transplant evaluation. Among patients who did not undergo angiography, 27% needed dialysis prior to transplantation at 2.4 ± 1.8 months after pre-transplant evaluation. CONCLUSIONS: Our results demonstrate a low risk of hastening the need for dialysis after coronary angiography in preemptive renal transplant candidates. Undergoing angiography had no effect on the ultimate need for or timing of dialysis initiation. These findings support completion of full cardiac evaluation as indicated for high-risk preemptive renal transplant candidates.

Serum sodium, renal function, and survival of patients with end-stage liver disease.

BACKGROUND & AIMS: Serum creatinine, a component of the model for end-stage liver disease (MELD), is an important prognostic indicator in patients with end-stage liver disease (ESLD). In addition, serum sodium has recently been recognized as an important predictor of mortality in patients with ESLD. We investigate the role of serum creatinine and sodium, and glomerular filtration rate (GFR) as determinants of survival in patients with ESLD. METHODS: A prospective database was utilized to identify all adults listed for primary liver transplantation (LTx) at the Mayo Clinic, Rochester, between 1990 and 1999. GFR was measured by iothalamate clearance. RESULTS: Among 837 patients listed for LTx, 660 had complete data including measured GFR. There was a significant association between GFR and survival after adjustment for MELD, with a linear rise in the risk of death as GFR decreased between 60 and 20ml/min/1.73m(2). Multivariable models showed that GFR is superior to creatinine in predicting mortality - a model consisting of total bilirubin (hazard ratio (HR)=2.17, p<0.01), INR (HR=3.26, p<0.01) and GFR (HR=0.42, p<0.01) was superior to MELD (chi-square 65.6 vs. 59.4, c-statistic 0.792 vs. 0.780). Serum sodium did not contribute to survival prediction when accurately measured GFR data were available. CONCLUSIONS: Serum concentrations of creatinine and sodium in patients with end-stage liver disease reflect a reduction in renal function, the underlying event that decreases survival.

Iothalamate quantification by tandem mass spectrometry to measure glomerular filtration rate.

BACKGROUND: Glomerular filtration rate (GFR) can be determined by measuring renal clearance of the radiocontrast agent iothalamate. Current analytic methods for quantifying iothalamate concentrations in plasma and urine using liquid chromatography or capillary electrophoresis have limitations such as long analysis times and susceptibility to interferences. We developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to overcome these limitations. METHODS: Urine and plasma samples were deproteinized using acetonitrile and centrifugation. The supernatant was diluted in water and analyzed by LC-MS/MS using a water:methanol gradient. We monitored 4 multiple reaction monitoring transitions: m/z 614.8-487.0, 614.8-456.0, 614.8-361.1, and 614.8-177.1. We compared the results to those obtained via our standard capillary electrophoresis (CE-UV) on samples from 53 patients undergoing clinical GFR testing. RESULTS: Mean recovery was 90%-110% in both urine and plasma matrices. Imprecision was

A prospective longitudinal analysis of cytomegalovirus (CMV)-specific CD4+ and CD8+ T cells in kidney allograft recipients at risk of CMV infection.

Cytomegalovirus (CMV)-specific cellular immunity is essential in controlling CMV infection after transplantation. We investigated whether CMV-specific T cell levels predict CMV DNAemia after kidney transplantation. Using cytokine-flow cytometry, we enumerated interferon-gamma producing CMV-specific CD4+ and CD8+ T cells at serial time points among CMV-mismatched (D+/R-) and seropositive (R+) kidney recipients who received 3 months of valganciclovir prophylaxis. Among 44 patients, eight (18%) developed CMV DNAemia at a mean (+ or - SD) time of 151 (+ or - 33) days after transplantation, including two (5%) with CMV syndrome and three (7%) with tissue-invasive CMV disease. Cox proportional hazards regression analysis showed that CMV mismatch (D+/R-) status (HR: 13, 95% CI: 1.6-106.4; P = 0.02) and diabetes mellitus (HR: 5.6; 95%CI: 1.1-27.9; P = 0.03) were significantly associated with CMV DNAemia. In contrast, the percentage or change-over-time in CMV-specific CD4+ [pp65 (P = 0.45), or CMV lysate (P = 0.22)] and CD8+ [pp65 (P = 0.43), or IE-1 (P = 0.37)] T cells were not significantly associated with CMV DNAemia. CMV-specific T cell assays have limited clinical utility among CMV R+ kidney recipients who received valganciclovir prophylaxis. On the other hand, the clinical utility of CMV-specific T cell assays will need to be assessed in a larger cohort of CMV D+/R- kidney recipients who remain at high-risk of delayed-onset CMV disease.

Comparison of urinary albumin quantification by immunoturbidimetry, competitive immunoassay, and protein-cleavage liquid chromatography-tandem mass spectrometry.

BACKGROUND: Increased urinary albumin excretion is a well-documented diagnostic and prognostic biomarker for renal disease. Urinary albumin is typically measured in clinical settings by immunoassay methods. However, neither a reference method nor a urine albumin calibration reference material is currently available. METHODS: We quantified urinary albumin in patient samples by using 3 commercially available reagent systems: DiaSorin SPQ and Beckman Coulter LX 20 (immunoturbidimetric), and Siemens Immulite (competitive immunoassay). Results were compared to values obtained by protein-cleavage liquid chromatography-tandem mass spectrometry (LC-MS/MS). RESULTS: In general, results from the 3 immunoassays agreed with results from LC-MS/MS. However, the SPQ results showed a negative bias across all ranges of albuminuria [(0-200 mg/L, y = 0.91x - 3.74 (CI 0.86-0.96); > 200 mg/L, y = 0.88x - 40.30 (CI 0.76-1.00)], whereas the LX 20 showed minimal bias in the 0-200 mg/L range [y = 0.97x - 88 (CI 0.92-1.02)] and the Immulite assay showed positive bias in the 0-200 mg/L range [y = 1.15x - 4.38 (CI 1.09-1.20)]. CONCLUSIONS: These results showed a reasonable quantification of urinary albumin by representative polyclonal and monoclonal immunoassays compared to an LC-MS/MS assay. In addition, the results do not suggest the presence of nonimmunoreactive albumin in urine. However, differences in analytic performance between assays support the need for a reference calibration material and reference method to standardize clinical laboratory measurements of urinary albumin.

Kidney transplantation for primary focal segmental glomerulosclerosis: outcomes and response to therapy for recurrence.

BACKGROUND: For a subset of adults and children with primary focal segmental glomerulosclerosis (FSGS), proteinuria and renal dysfunction recur after kidney transplantation (KTx). Predicting recurrence and response to plasmapheresis (PP) or other interventions remains problematic. METHODS: The prevalence, recurrence rate, outcomes, and treatment responses of patients with FSGS were determined among 1573 KTx recipients. Although 5.0% carried some diagnosis of FSGS, only 1.9% (n=30) met strict diagnostic criteria for primary FSGS including biopsy-proven FSGS, lack of secondary factors, negative family history, and progression to end-stage renal disease within 10 years. RESULTS: Of these, 47% had recurrent FSGS compared with 8% of those not meeting strict criteria (P<0.001). Recurrence was more common in children compared with adults (86% vs. 35%, P=0.01). Graft survival was lower for recipients with primary FSGS compared with all others and inferior graft survival was attributable to recurrent FSGS. Fourteen patients received PP preemptively (pre-KTx) or therapeutically (post-KTx) for recurrent disease. Four pediatric patients additionally received anti-CD20 (rituximab) therapy. Of the different treatment approaches, only PP combined with rituximab was associated with prolonged remission of proteinuria. CONCLUSIONS: The results indicate that patients at high risk for FSGS recurrence can be identified and may benefit from carefully planned peritransplant interventions.

Quantification of urinary albumin by using protein cleavage and LC-MS/MS.

BACKGROUND: Urinary albumin excretion is a sensitive diagnostic and prognostic marker for renal disease. Therefore, measurement of urinary albumin must be accurate and precise. We have developed a method to quantify intact urinary albumin with a low limit of quantification (LOQ). METHODS: We constructed an external calibration curve using purified human serum albumin (HSA) added to a charcoal-stripped urine matrix. We then added an internal standard, (15)N-labeled recombinant HSA ((15)NrHSA), to the calibrators, controls, and patient urine samples. The samples were reduced, alkylated, and digested with trypsin. The concentration of albumin in each sample was determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and linear regression analysis, in which the relative abundance area ratio of the tryptic peptides (42)LVNEVTEFAK(51) and (526)QTALVELVK(534) from albumin and (15)NrHSA were referenced to the calibration curve. RESULTS: The lower limit of quantification was 3.13 mg/L, and the linear dynamic range was 3.13-200 mg/L. Replicate digests from low, medium, and high controls (n = 5) gave intraassay imprecision CVs of 2.8%-11.0% for the peptide (42)LVNEVTEFAK(51), and 1.9%-12.3% for the (526)QTALVELVK(534) peptide. Interassay imprecision of the controls for a period of 10 consecutive days (n = 10) yielded CVs of 1.5%-14.8% for the (42)LVNEVTEFAK(51) peptide, and 6.4%-14.1% for the (526)QTALVELVK(534) peptide. For the (42)LVNEVTEFAK(51) peptide, a method comparison between LC-MS/MS and an immunoturbidometric method for 138 patient samples gave an R(2) value of 0.97 and a regression line of y = 0.99x + 23.16. CONCLUSIONS: Urinary albumin can be quantified by a protein cleavage LC-MS/MS method using a (15)NrHSA internal standard. This method provides improved analytical performance in the clinically relevant range compared to a commercially available immunoturbidometric assay.

Comparison between immunoturbidimetry, size-exclusion chromatography, and LC-MS to quantify urinary albumin.

BACKGROUND: The accurate and precise measurement of urinary albumin is critical, since even minor increases are diagnostically sensitive indicators of renal disease, cardiovascular events, and risk for death. To gain insights into potential measurement biases, we systematically compared urine albumin measurements performed by LC-MS, a clinically available immunoturbidimetric assay, and size-exclusion HPLC. METHODS: We obtained unused clinical urine samples from 150 patients who were stratified by degrees of albuminuria (<20 mg/L, 20-250 mg/L, >250 mg/L) as determined by the immunoturbidimetric assay used in our clinical laboratory (Roche Hitachi 912). Urine albumin was then remeasured via LC-MS and HPLC (Accumin) assays. RESULTS: The immunoturbidimetric assay, calibrated using manufacturer-supplied serum-derived calibrators (Diasorin), underestimated albumin compared with LC-MS. After calibration with purified HSA, this immunoturbidimetric assay correlated well with LC-MS. HPLC overestimated albumin compared with both LC-MS and immunoturbidimetry. The current LC-MS and HPLC assays both performed poorly at concentrations <20 mg/L. CONCLUSIONS: Efforts are needed to establish gold-standard traceable calibrators for clinical assays. LC-MS is a specific method to quantify albumin in native urine when concentrations exceed 20 mg/L, and therefore could be employed for standardization among assays.