Publications by authors named "Mehmet U S Ayvaci"

Work relative value unit (wRVU)-based fee schedules are predominantly used by both the Centers for Medicare & Medicaid Services (CMS) and private payers to determine the payments for physicians' clinical productivity. However, under the Affordable Care Act, CMS is transitioning into a value-based payment structure that rewards patient-oriented outcomes and cost savings. Moreover, in the context of solid organ transplantation, physicians and surgeons conduct many activities that are neither billable nor accounted for in the wRVU models.

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Background: The practice of induction therapy with either rabbit anti-thymocyte globulin (r-ATG) or interleukin-2 receptor antagonists (IL-2RA) is common among heart transplant recipients. However, its benefits in the setting of contemporary maintenance immunosuppression with tacrolimus/mycophenolic acid (TAC/MPA) are unknown.

Methods: We compared post-transplant mortality among three induction therapy strategies (r-ATG vs IL2-RA vs no induction) in a retrospective cohort analysis of heart transplant recipients maintained on TAC/MPA in the Organ Procurement Transplant Network (OPTN) database between the years 2006 and 2015.

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ecision models representing the clinical situations where treatment options entail a significant risk of morbidity or mortality should consider the variations in risk preferences of individuals. In this study, we develop a stochastic modeling framework that optimizes risk-sensitive diagnostic decisions after a mammography exam. For a given patient, our objective is to find the utility maximizing diagnostic decisions where we define the utility over quality-adjusted survival duration.

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Background: The survival benefit from simultaneous liver-kidney transplantation (SLK) over liver transplant alone (LTA) in recipients with moderate renal dysfunction is not well understood. Moreover, the impact of deceased donor organ quality in SLK transplant survival has not been well described in the literature.

Methods: The Scientific Registry of Transplant Recipients was studied for adult recipients receiving LTA (N=2,700) or SLK (N=1,361) transplantation with moderate renal insufficiency between 2003 and 2013.

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Background: Induction therapy in deceased donor kidney transplantation is costly, with wide discrepancy in utilization and a limited evidence base, particularly regarding cost-effectiveness.

Methods: We linked the United States Renal Data System data set to Medicare claims to estimate cumulative costs, graft survival, and incremental cost-effectiveness ratio (ICER - cost per additional year of graft survival) within 3 years of transplantation in 19 450 deceased donor kidney transplantation recipients with Medicare as primary payer from 2000 to 2008. We divided the study cohort into high-risk (age > 60 years, panel-reactive antibody > 20%, African American race, Kidney Donor Profile Index > 50%, cold ischemia time > 24 hours) and low-risk (not having any risk factors, comprising approximately 15% of the cohort).

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Background And Objectives: IL-2 receptor antagonist (IL2-RA) is recommended as a first-line agent for induction therapy in renal transplantation. However, this remains controversial in deceased donor renal transplantation (DDRT) maintained on tacrolimus (TAC)/mycophenolic acid (MPA) with or without steroids.

Design, Setting, Participants, & Measurements: We studied the United Network for Organ Sharing Registry for patients receiving DDRT from 2000 to 2012 maintained on TAC/MPA at transplantation hospital discharge (n=74,627) to compare outcomes of IL2-RA and other induction agents.

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Background And Objectives: Induction therapy with IL-2 receptor antagonist (IL2-RA) is recommended as a first line agent in living donor renal transplantation (LRT). However, use of IL2-RA remains controversial in LRT with tacrolimus (TAC)/mycophenolic acid (MPA) with or without steroids.

Design, Setting, Participants, & Measurements: The Organ Procurement and Transplantation Network registry was studied for patients receiving LRT from 2000 to 2012 maintained on TAC/MPA at discharge (n=36,153) to compare effectiveness of IL2-RA to other induction options.

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Background: Increasing focus on potentially unnecessary diagnosis and treatment of certain breast cancers prompted our investigation of whether clinical and mammographic features predictive of invasive breast cancer versus ductal carcinoma in situ (DCIS) differ by age.

Methods: We analyzed 1,475 malignant breast biopsies, 1,063 invasive and 412 DCIS, from 35,871 prospectively collected consecutive diagnostic mammograms interpreted at University of California, San Francisco between 1/6/1997 and 6/29/2007. We constructed three logistic regression models to predict the probability of invasive cancer versus DCIS for the following groups: women ≥ 65 (older group), women 50-64 (middle age group), and women < 50 (younger group).

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This study aims to determine the most informative mammographic features for breast cancer diagnosis using mutual information (MI) analysis. Our Health Insurance Portability and Accountability Act-approved database consists of 44,397 consecutive structured mammography reports for 20,375 patients collected from 2005 to 2008. The reports include demographic risk factors (age, family and personal history of breast cancer, and use of hormone therapy) and mammographic features from the Breast Imaging Reporting and Data System lexicon.

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Purpose: We evaluated the cost-effectiveness of adjuvant chemotherapy using 5-fluorouracil, leucovorin (5FU/LV), and oxaliplatin (FOLFOX) compared with 5FU/LV alone and 5FU/LV compared with observation alone for patients who had resected stage II colon cancer.

Methods: We developed 2 Markov models to represent the adjuvant chemotherapy and follow-up periods and a single Markov model to represent the observation group. We used calibration to estimate the transition probabilities among different toxicity levels.

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We develop a finite-horizon discrete-time constrained Markov decision process (MDP) to model diagnostic decisions after mammography where we maximize the total expected quality-adjusted life years (QALYs) of a patient under resource constraints. We use clinical data to estimate the parameters of the MDP model and solve it as a mixed-integer program. By repeating optimization for a sequence of budget levels, we calculate incremental cost-effectiveness ratios attributable to consecutive levels of funding and compare actual clinical practice with optimal decisions.

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