About

Brad Astor is a Professor of Population Health Sciences and a Professor of Nephrology at the University of Wisconsin–Madison. His research focuses on various aspects of kidney disease and its interaction with cardiovascular disease. He has a particular interest in biomarkers of kidney function and their associations with clinical outcomes, including incident chronic kidney disease, cardiovascular disease, and mortality. His research has been conducted in diverse populations, including the general population through studies such as the Atherosclerosis Risk in Communities (ARIC) Study and the Multi-Ethnic Study of Atherosclerosis (MESA), as well as in clinical trials like the African American Study of Kidney Disease and Hypertension (AASK), and observational studies of dialysis patients such as the Choices for Healthy Outcomes in Caring for ESRD (CHOICE). Additionally, he investigates predictors of outcomes in kidney transplant recipients using data from the Wisconsin Allograft Recipient Database (WisARD), and he studies hemodialysis vascular access complications. Astor is affiliated with the Department of Medicine, Division of Nephrology, and the Department of Population Health Sciences at UWSMPH, and has collaborations with Johns Hopkins Bloomberg School of Public Health and Johns Hopkins University School of Medicine.

Research topics

• Internal medicine
• Medicine
• Pathology
• Intensive care medicine
• Family medicine
• Emergency medicine
• Surgery

Selected publications

• Qualified prediction system for allograft failure in real world settings: extended validation study

  BMJ Medicine · 2026-05-01

  articleOpen access

  Objective To perform comprehensive validations of the integrative Box (iBox) system, a prediction model for long term risk of kidney allograft failure, for extension of its context of use in clinical trials as well as for its wider implementation in clinical practice. Design Extended validation study. Setting Paris Transplant Group database (comprising kidney recipients with transplantations between 1 January 2005 and 1 January 2014) and European, North American, and South American hospitals (comprising recipients of kidneys transplanted beween 1 January 2000 and 1 January 2022). Patients were followed until 1 November 2024. Participants 12 683 kidney tranplant recipients from 21 academic centres in Europe, North America, and South America; 4000 patients in the derivation cohort and 8683 in the validation cohorts. Main outcome measures Performance of the iBox, including flexible iBox versions in specific clinical contexts (race-free estimated glomerular filtration rate (eGFR) equations (ie, without including race as a factor in the calculation), in specific clinical contexts (initial nephropathy recurrence, BK virus associated nephropathy, and different immunosuppressive strategies), and over-extended follow-up periods. Predictive performance was assessed by discrimination, calibration, overall fit, and clinical utility. Results 12 683 kidney transplant recipients were included in the study (n=4000 in the derivation cohort and n=8683 in the validation cohorts). Median follow-up time after risk evaluation was 5.78 years (interquartile range (IQR) 3.51-7.00) in the derivation cohort and 4.68 years (2.48-7.00) in the validation cohorts. 549 (13.7%) and 991 (11.4%) patients had graft loss in the derivation and validation cohorts, respectively. All versions of the iBox algorithm maintained good discrimination and overall fit performance in the derivation and validation cohorts (C index range 0.79-0.87, Brier scores 0.08-0.11). Calibration was adequate in some but not all external validation cohorts, with trends toward overestimation or underestimation of predicted risks. Decision curve analysis showed positive and comparable net benefit for all iBox algorithms across decision thresholds up to 40% in the derivation cohort (net benefit 0.07-0.08 at 20% threshold) and validation cohorts (net benefit 0.03-0.11 at 20% threshold). Accounting for the competing risk of death with a functioning graft resulted in similar performance, except for calibration which varied across cohorts, without any model consistently outperforming any other model. The model performed well with different race-free eGFR equations (C index 0.81), in various clinical scenarios, including disease recurrence and BK virus nephropathy, with different immunosuppressive strategies, such as calcineurin inhibitors and mTOR (mechanistic target of rapamycin) inhibitors (C index range 0.74-0.87), and when extending the prediction period to 10 years after risk evaluation (C index 0.79). The iBox predictive performance was not modified when various histological indices were used. The iBox was also superior to eGFR slope (C index 0.81 v 0.62) and circulating anti-HLA donor specific antibodies (C index 0.81 v 0.57) in its predictive ability. Conclusions In this study, the robust predictive performance of the iBox system across diverse real world settings and clinical scenarios was shown. These results highlight the versatility and reliability of the iBox system, and support its use for risk stratification in routine clinical practice and as a surrogate endpoint for clinical trials.

  PublisherDOI

• Association of recipient age with deceased donor kidney transplant outcomes in a single-center cohort

  Clinical Nephrology · 2026-04-23

  article

  INTRODUCTION: As the number of elderly patients with end-stage kidney disease (ESKD) increases, the importance of understanding how age affects post-transplant success grows. We sought to quantify the association of age with key outcomes in deceased donor kidney transplant (DDKT) recipients. MATERIALS AND METHODS: We did a single-center retrospective cohort analysis of all DDKT recipients who received kidneys between January 2001 and June 2021, stratified by age into 4 groups (18 - 49, 50 - 59, 60 - 69, ≥ 70). Outcomes of interest included uncensored graft failure (UCGF), death-censored graft failure (DCGF), and death with a functioning graft (DWFG) within 5 years of transplant and acute rejection (AR) within 1 year of transplant. RESULTS: Of 3,119 recipients, 1,192 (38.2%) were 18 - 49 years old (reference group), 947 (30.4%) were 50 - 59, 795 (25.5%) were 60 - 69, and 185 (5.9%) were ≥ 70. The adjusted hazard ratio (aHR) for UCGF was 1.22 (95% CI: 1.01 - 1.48) for 50 - 59 years; 1.78 (95% CI: 1.47 - 2.17) for 60 - 69; and 2.83 (95% CI: 2.13 - 3.76) for ≥ 70. The aHR for DCGF was only statistically significant for the ≥ 70 age group at 1.73 (95% CI: 1.16 - 2.96). The aHR for DWFG was 2.00 (95% CI: 1.47 - 2.73) for 50 - 59 years; 3.36 (95% CI: 2.47 - 4.58) for 60 - 69; and 5.45 (95% CI: 3.95 - 8.26) for ≥ 70. The aHR for AR was 0.73 (95% CI: 0.61 - 0.88) for 50 - 59 years; 0.69 (95% CI: 0.56 - 0.84) for 60 - 69; and 0.47 (95% CI: 0.31 - 0.72) for ≥ 70. CONCLUSION: DDKT recipients over the age of 70 are at a higher risk of UCGF, DCGF, and DWFG but have a lower risk of AR than their younger counterparts.

  PublisherDOI

• Kidney transplantation after prostate cancer treatment: A multi-institutional collaborative

  Surgery · 2026-04-30

  articleOpen access
  PublisherDOI

• Assessment of colorectal cancer recurrence risk following solid organ transplantation

  Journal of Gastrointestinal Oncology · 2026-04-01

  articleOpen access

  Background: Prior studies have reported solid organ transplant (SOT) recipients have increased rates of colorectal cancer (CRC). While this increased incidence is established, the recurrence risk following curative-intent treatment for post-SOT CRC remains poorly defined. Therefore, the aim of this study was to evaluate CRC recurrence in addition to exploring clinical and molecular factors associated with CRC recurrence in patients with prior SOT. Methods: Multi-institutional retrospective cohort study of adult patients diagnosed with CRC following prior SOT between 2016-2025 at The Johns Hopkins Hospital and the University of Wisconsin Hospitals and Clinics. Demographic, clinical, molecular genomics, and immunosuppression data were obtained from electronic medical records. Recurrence risk was compared to population study benchmark recurrence rates using standardized incidence ratios (SIRs). Results: This study included 53 SOT recipients with subsequent CRC diagnosis. Recurrence rates exceeded population benchmarks across all disease stages, particularly in stage I and II disease demonstrating SIRs of 3.66 and 2.55 respectively. KRAS and APC mutations were associated with increased recurrence risk [hazard ratio (HR) =13.58, P=0.002; HR =5.03, P=0.02, respectively], while no patients with BRAF mutations recurred (n=8, P<0.001). All BRAF mutations occurred in tumors that were mismatch repair deficient (MMRd). Mismatch repair (MMR) status and immunosuppression characteristics did not predict disease recurrence in the study cohort. Conclusions: SOT recipients showed a trend towards heightened CRC recurrence risk compared to population benchmarks. KRAS, APC, and BRAF mutational status all influenced recurrence risk in this cohort. Despite a lack of association between immunosuppression variables and recurrence, we suspect diminished immune surveillance is implicated in this elevated relapse risk. Strategies to address this, including immunosuppression reduction in the post-SOT CRC population, may be effective in reducing this elevated relapse risk but require validation in prospective multi-institutional studies.

  PublisherDOI

• Assessing the Predictive Ability of the Living Kidney Donor Profile Index for Graft Survival

  American Journal of Transplantation · 2025-08-01

  article
  PublisherDOI

• Hydroxychloroquine Associated With Lower Glomerular Filtration Rate Decline in Lupus Nephritis

  Arthritis Care & Research · 2025-07-21

  articleOpen access

  Objective Hydroxychloroquine (HCQ) protects kidney function in lupus nephritis (LN) by preventing flares, yet some cohort studies show no significant benefit in kidney function with HCQ. Clarifying these conflicting findings by showing early and long‐term benefits of HCQ on kidney function preservation is critical. Therefore, we analyzed data from our retrospective longitudinal inception LN cohort to examine the time‐varying effects of HCQ on kidney function decline in LN. Methods We analyzed retrospective data from an incident biopsy‐proven LN cohort. Creatinine values at LN diagnosis through the last follow‐up were abstracted to find the estimated glomerular filtration rate (eGFR). Using HCQ exposure as a time‐dependent covariate, we examined associations between HCQ exposure and sustained eGFR decline ≥30% and ≥40%. We also calculated an annual eGFR slope decline by HCQ exposure using linear mixed‐effects analysis. Results Among 209 patients, 33% and 23% experienced eGFR decline ≥30% and ≥40% over time. Time‐varying HCQ exposure was associated with a 60% and 62% lower risk of eGFR decline of ≥30% or ≥40%, after adjusting for propensity scores. A 77% lower risk of eGFR decline was noted in patients with chronic kidney disease (CKD) stage ≥3 with HCQ. HCQ exposure reduced the annual eGFR slope decline by 5.12 and 3.17 mL/min/1.73 m 2 within the first 5 and 10 years of diagnosis. Conclusion HCQ use was associated with early and long‐term benefits on kidney function in LN, including those with CKD stage ≥3. Universal HCQ use should be encouraged in LN patients. image

  PublisherOA PDFDOI

• Detrimental Outcomes Associated with Kidney Delayed Graft Function Persist Beyond the Short-Term

  Journal of the American Society of Nephrology · 2025-10-01

  article

  Background: Delayed graft function (DGF) is associated with acute rejection and decreased graft survival mainly in the early post-transplant period. However, its impact beyond this time is not well known. Methods: All deceased donor kidney-only transplant recipients at our center between 01/2000 and 06/2021 were stratified based on DGF status (+ vs. –). Adjusted hazard ratios (aHR) of uncensored graft failure (UGF), death-censored graft failure (DCGF), death with a functioning graft (DWFG), and acute rejection (AR) were analyzed within the short-term (0-6 months) and mid-term (7-36 months). Results: Out of 3093 recipients, 894 (28.9%) experienced DGF. Table 1 contains the aHR values for DGF + recipients comparing all four outcomes in the short- and mid-term. In the short-term, DGF was associated with an increased risk for UGF, DCGF, DWFG, and AR. Even in the mid-term outcomes, DGF was associated with an increased risk for UGF (aHR: 1.41, 95% CI: 1.13-1.77) and DWFG (aHR: 1.60, 95% CI: 1.15-2.36), but not for DCGF (aHR: 1.25, 95% CI: 0.93-1.70) or AR (aHR: 1.11, 95% CI: 0.78-1.58) [Table 1]. Figure 1 contains the Kaplan-Meier curves comparing the outcomes among DGF + and – recipients over 36 months. Conclusion: Recipients with DGF remained at significantly higher risk of UGF and DWFG beyond the first 6 months, although the associations were weaker than during the first 6 months. Close follow-up for patients with DGF may mitigate these mid-term outcomes.Table 1: Association of DGF with short- and mid-term outcomesFigure 1: Kaplan-Meier Curves of Outcomes

  PublisherDOI

• Five years outcomes of recipients of dual kidney transplantation are better compared to the single kidney transplantation with comparable early post-transplant complications

  American Journal of Transplantation · 2025-01-01

  articleOpen access
  PublisherOA PDFDOI

• Postkidney Transplant Delayed Graft Function Outcomes Are Not Worsened by Deceased Donor Type

  Clinical Transplantation · 2025-05-30 · 5 citations

  articleOpen access

  INTRODUCTION: Kidney-delayed graft function (DGF) is more common in donation after circulatory death (DCD) donors in comparison to donatation after brain death (DBD). We analyzed deceased kidney transplant recipients (DDKTR) at our center between 2005 and 2019, stratified by donor type (DBD vs. DCD). METHODS: We assessed risk factors for DGF, acute rejection (AR), graft failure (GF), along with the death with functioning graft (DWFG), and the interaction between types of donors for those complications. RESULTS: Among 2543 DDKTRs, 804 (32%) were from DCD donors. Older donor age, higher recipient body mass index, and receipt of a depleting induction agent were associated with increased risk for DGF in both DBD and DCD. In contrast, preemptive transplant and female recipient gender were associated with reduced risk. Additional risk factors in DBD, but not in DCD recipients, included higher donor terminal serum creatinine, higher kidney donor profile index, right donor kidney, and prolonged cold ischemia time. Female donors were associated with a reduced risk of DGF only among DCD donors. DGF was associated with higher AR and GF, with no significant differences across donor types, DBD vs. DCD (AR: adjusted hazard ratio [aHR] 2.22 vs. 2.37, p-interaction = 0.65; GF: 3.04 vs. 2.56; p-interaction = 0.47). DGF was associated with a higher risk for DWFG among DBD (aHR: 3.43, 95% CI: 1.96-6.00, p < 0.001) but not with DCD (aHR: 1.90, 95% CI: 0.78-4.61, p = 0.16), with p-interaction of 0.15 CONCLUSION: Despite higher DGF rates in DCD, early adverse outcomes after DGF were similar between deceased donor types and should not deter the utilization of DCD kidneys.

  PublisherOA PDFDOI

• Associations of retention in care by visits or lupus-specific labs with acute care among young adults: A medicare cohort study

  Lupus · 2025-07-18

  articleOpen access

  Objective While quality lupus care is associated with lower lupus-related damage, the impact of access and process quality measures on other lupus outcomes remains unclear. Given high acute care in young adults, our objective was to evaluate two process quality measures, visit-based retention in lupus care and receipt of lupus-specific serologic testing, and associations with subsequent acute care use. Methods This cohort study used a 20% national sample of young adult (ages 18–35) Medicare beneficiaries with lupus to first measure visit-based retention in rheumatology care and receipt of ≥1 complement or dsDNA test over 1 year. Acute care use (Emergency Department visits and hospitalizations) was then assessed in the subsequent 6 months. Associations of visit-based retention and serologic testing with acute care were evaluated with Cox regressions. Results Among 1036 young adults with lupus, acute care use was very high – nearly 60% at 6 months. Observed acute care-free survival time was longer in patients who had visit-based retention (154 vs 104 days, p = 0.02) or serologic testing (166 vs 101 days, p = 0.002). Only 28% of beneficiaries had serologic testing, but this was associated with 21% lower incidence of acute care (aHR 0.79, 95% CI 0.65, 0.97) after adjustment; visit-based retention was not associated with acute care after adjustment. Conclusion Receipt of complement or dsDNA antibody testing, a lupus-specific care quality indicator, was associated with reduced acute care use in young adults. Improving lupus care quality measures, like complement or dsDNA testing, may improve lupus outcomes including reduced acute care use.

  PublisherOA PDFDOI

Recent grants

• 1/14 APOL1 Long-term Kidney Transplantation Outcomes Network (APOLLO) Clinical Center

  NIH · $1.7M · 2017–2028

• Dynamic Prediction of Renal Failure Using Longitudinal Prognostic Information among Patients with Chronic Kidney Disease and Kidney Transplant

  NIH · $1.3M · 2019–2024

• NIH Grant R21DK078218

  NIH · $320k · 2013

• NIH Grant R01DK076770

  NIH · $2.2M · 2015

• NIH Grant R01DK07677002

  NIH · $708k · 2012

Frequent coauthors

• Josef Coresh

  Bloomberg (United States)

  759 shared

• Aaron R. Folsom

  University of Minnesota

  504 shared

• Kunihiro Matsushita

  Johns Hopkins University

  394 shared

• Michael G. Shlipak

  University of California, San Francisco

  354 shared

• Ron T. Gansevoort

  University Medical Center Groningen

  277 shared

• Mark Woodward

  George Institute for Global Health

  264 shared

• Bakhtawar K. Mahmoodi

  Erasmus MC

  261 shared

• Christie M. Ballantyne

  Baylor College of Medicine

  245 shared