Defining the Need for Causal Inference to Understand the Impact of Social Determinants of Health: A Primer on Behalf of the Consortium for the Holistic Assessment of Risk in Transplantation (CHART)

Objective

This study aims to introduce key concepts and methods that inform the design of studies that seek to quantify the causal effect of social determinants of health (SDOH) on access to and outcomes following organ transplant.

Background

The causal pathways between SDOH and transplant outcomes are poorly understood. This is partially due to the unstandardized and incomplete capture of the complex interactions between patients, their neighborhood environments, the tertiary care system, and structural factors that impact access and outcomes. Designing studies to quantify the causal impact of these factors on transplant access and outcomes requires an understanding of the fundamental concepts of causal inference.

Methods

We present an overview of fundamental concepts in causal inference, including the potential outcomes framework and direct acyclic graphs. We discuss how to conceptualize SDOH in a causal framework and provide applied examples to illustrate how bias is introduced.

Results

There is a need for direct measures of SDOH, increased measurement of latent and mediating variables, and multi-level frameworks for research that examine health inequities across multiple health systems to generalize results. We illustrate that biases can arise due to socioeconomic status, race/ethnicity, and incongruencies in language between the patient and clinician.

Conclusions

Progress towards an equitable transplant system requires establishing causal pathways between psychosocial risk factors, access, and outcomes. This is predicated on accurate and precise quantification of social risk, best facilitated by improved organization of health system data and multicenter efforts to collect and learn from it in ways relevant to specialties and service lines.

Social network interventions to reduce race disparities in living kidney donation: Design and rationale of the friends and family of kidney transplant patients study (FFKTPS)

INTRODUCTION

Racial/ethnic disparities in living donor kidney transplantation (LDKT) are a persistent challenge. Although nearly all directed donations are from members of patients' social networks, little is known about which social network members take steps toward living kidney donation, which do not, and what mechanisms contribute to racial/ethnic LDKT disparities.

METHODS

We describe the design and rationale of the Friends and Family of Kidney Transplant Patients Study, a factorial experimental fielding two interventions designed to promote LKD discussions. Participants are kidney transplant candidates at two centers who are interviewed and delivered an intervention by trained center research coordinators. The search intervention advises patients on which social network members are most likely to be LKD contraindication-free; the script intervention advises patients on how to initiate effective LKD discussions. Participants are randomized into four conditions: no intervention, search only, script only, or both search and script. Patients also complete a survey and optionally provide social network member contact information so they can be surveyed directly. This study will seek to enroll 200 transplant candidates. The primary outcome is LDKT receipt. Secondary outcomes include live donor screening and medical evaluations and outcomes. Tertiary outcomes include LDKT self-efficacy, concerns, knowledge, and willingness, measured before and after the interventions.

CONCLUSION

This study will assess the effectiveness of two interventions to promote LKD and ameliorate Black-White disparities. It will also collect unprecedented information on transplant candidates' social network members, enabling future work to address network member structural barriers to LKD.

Increasing Obesity Prevalence in the United States End-Stage Renal Disease Population

Background

Among ESRD patients, obesity may improve dialysis-survival but decreases likelihood of transplantation, and as such, obesity prevalence may directly affect growth of the dialysis population.

Objective

The objective of this study was to assess BMI trends in the ESRD population as compared to the general population.

Materials and Methods

Incident adult ESRD patients were identified from the United States Renal Data System from 01/01/1995-12/31/2010 (n=1,458,350). Data from the Behavioral Risk Factor Surveillance System (n=4,303,471) represented the US population. Trends in BMI, obesity classes I (BMI of 30-34.9), II (BMI of 35-39.9), and III (BMI ≥ 40), were examined by year of dialysis initiation. Trends in BMI slope were compared between the ESRD and US populations using linear regression.

Results

Mean BMI of ESRD patients in 1995 was 25.2 as compared to 29.4 in 2010, a 16.7% increase, while the US population's mean BMI increased from 25.3 to 27.2, a 7.5% increase. BMI increase among the ESRD population was significantly more rapid than among the US population (β: 0.16, 95% CI: 0.14-0.18, p<0.001).

Conclusions and Recommendations

Mean BMI among the ESRD population is increasing more rapidly than the US population. Given decreased access to kidney transplantation among ESRD patients with obesity, future research should be directed at controlling healthcare expenditures by identifying strategies to address the obesity epidemic among the US ESRD population.

Impact of Protease Inhibitor-Based Anti-Retroviral Therapy on Outcomes for HIV+ Kidney Transplant Recipients

Excellent outcomes have been demonstrated among select HIV-positive kidney transplant (KT) recipients with well-controlled infection, but to date, no national study has explored outcomes among HIV+ KT recipients by antiretroviral therapy (ART) regimen. Intercontinental Marketing Services (IMS) pharmacy fills (1/1/01-10/1/12) were linked with Scientific Registry of Transplant Recipients (SRTR) data. A total of 332 recipients with pre- and posttransplantation fills were characterized by ART at the time of transplantation as protease inhibitor (PI) or non-PI-based ART (88 PI vs. 244 non-PI). Cox proportional hazards models were adjusted for recipient and donor characteristics. Comparing recipients by ART regimen, there were no significant differences in age, race, or HCV status. Recipients on PI-based regimens were significantly more likely to have an Estimated Post Transplant Survival (EPTS) score of >20% (70.9% vs. 56.3%, p = 0.02) than those on non-PI regimens. On adjusted analyses, PI-based regimens were associated with a 1.8-fold increased risk of allograft loss (adjusted hazard ratio [aHR] 1.84, 95% confidence interval [CI] 1.22-2.77, p = 0.003), with the greatest risk observed in the first posttransplantation year (aHR 4.48, 95% CI 1.75-11.48, p = 0.002), and a 1.9-fold increased risk of death as compared to non-PI regimens (aHR 1.91, 95% CI 1.02-3.59, p = 0.05). These results suggest that whenever possible, recipients should be converted to a non-PI regimen prior to kidney transplantation.

doublesex is a mimicry supergene

One of the most striking examples of sexual dimorphism is sex-limited mimicry in butterflies, a phenomenon in which one sex--usually the female--mimics a toxic model species, whereas the other sex displays a different wing pattern. Sex-limited mimicry is phylogenetically widespread in the swallowtail butterfly genus Papilio, in which it is often associated with female mimetic polymorphism. In multiple polymorphic species, the entire wing pattern phenotype is controlled by a single Mendelian 'supergene'. Although theoretical work has explored the evolutionary dynamics of supergene mimicry, there are almost no empirical data that address the critical issue of what a mimicry supergene actually is at a functional level. Using an integrative approach combining genetic and association mapping, transcriptome and genome sequencing, and gene expression analyses, we show that a single gene, doublesex, controls supergene mimicry in Papilio polytes. This is in contrast to the long-held view that supergenes are likely to be controlled by a tightly linked cluster of loci. Analysis of gene expression and DNA sequence variation indicates that isoform expression differences contribute to the functional differences between dsx mimicry alleles, and protein sequence evolution may also have a role. Our results combine elements from different hypotheses for the identity of supergenes, showing that a single gene can switch the entire wing pattern among mimicry phenotypes but may require multiple, tightly linked mutations to do so.

A partitioned likelihood analysis of swallowtail butterfly phylogeny (Lepidoptera:Papilionidae)

Although it is widely agreed that data from multiple sources are necessary to confidently resolve phylogenetic relationships, procedures for accommodating and incorporating heterogeneity in such data remain underdeveloped. We explored the use of partitioned, model-based analyses of heterogeneous molecular data in the context of a phylogenetic study of swallowtail butterflies (Lepidoptera: Papilionidae). Despite substantial basic and applied study, phylogenetic relationships among the major lineages of this prominent group remain contentious. We sequenced 3.3 kb of mitochondrial and nuclear DNA (2.3 kb of cytochrome oxidase I and II and 1.0 kb of elongation factor-1 alpha, respectively) from 22 swallowtails, including representatives of Baroniinae, Parnassiinae, and Papilioninae, and from several moth and butterfly outgroups. Using parsimony, we encountered considerable difficulty in resolving the deepest splits among these taxa. We therefore chose two outgroups with undisputed relationships to each other and to Papilionidae and undertook detailed likelihood analyses of alternative topologies. Following from previous studies that have demonstrated substantial heterogeneity in the evolutionary dynamics among process partitions of these genes, we estimated evolutionary parameters separately for gene-based and codon-based partitions. These values were then used as the basis for examining the likelihoods of possible resolutions and rootings under several partitioned and unpartitioned likelihood models. Partitioned models gave markedly better fits to the data than did unpartitioned models and supported different topologies. However, the most likely topology varied from model to model. The most likely ingroup topology under the best-fitting, six-partition GTR + gamma model favors a paraphyletic Parnassiinae. However, when examining the likelihoods of alternative rootings of this tree relative to rootings of the classical hypothesis, two rootings of the latter emerge as most likely. Of these two, the most likely rooting is within the Papilioninae, although a rooting between Baronia and the remaining Papilionidae is only nonsignificantly less likely.

Interaction of process partitions in phylogenetic analysis: an example from the swallowtail butterfly genus Papilio

In this study, we explored how the concept of the process partition may be applied to phylogenetic analysis. Sequence data were gathered from 23 species and subspecies of the swallowtail butterfly genus Papilio, as well as from two outgroup species from the genera Eurytides and Pachliopta. Sequence data consisted of 1,010 bp of the nuclear protein-coding gene elongation factor-1 alpha (EF-1 alpha) as well as the entire sequences (a total of 2,211 bp) of the mitochondrial protein-coding genes cytochrome oxidase I and cytochrome oxidase II (COI and COII). In order to examine the interaction between the nuclear and mitochondrial partitions in a combined analysis, we used a method of visualizing branch support as a function of partition weight ratios. We demonstrated how this method may be used to diagnose error at different levels of a tree in a combined maximum-parsimony analysis. Further, we assessed patterns of evolution within and between subsets of the data by implementing a multipartition maximum-likelihood model to estimate evolutionary parameters for various putative process partitions. COI third positions have an estimated average substitution rate more than 15 times that of EF-1 alpha, while COII third positions have an estimated average substitution rate more than 22 times that of EF-1 alpha. Ultimately, we found that although the mitochondrial and nuclear data were not significantly incongruent, homoplasy in the fast-evolving mitochondrial data confounded the resolution of basal relationships in the combined unweighted parsimony analysis despite the fact that there was relatively strong support for the relationships in the nuclear data. We conclude that there may be shortcomings to the methods of "total evidence" and "conditional combination" because they may fail to detect or accommodate the type of confounding bias we found in our data.

A standards of care plan in the postanesthesia care unit

Every patient is entitled to consistent, high-quality, individualized care. The PACU staff and former director of staff education at Southwestern Vermont Medical Center developed a documentation tool to achieve this end. The primary focus of the tool is on standards of care with an emphasis on outcome standards. Every patient received and cared for in the PACU is evaluated in terms of these outcome standards. If for any reason an outcome standard is not achieved, appropriate action is taken. The four-page bifold tool incorporates the nursing process. Potential nursing diagnostic problems are described and assessment and intervention data are integrated accordingly. The plan is further individualized vis à vis nursing progress notes. The tool has been in use for well over 1 year, and quality assurance studies demonstrate that outcome standards achieved and not achieved are consistently documented. The PACU staff believe this tool has enhanced professional practice and improved use of the nursing process and standards of care.

Energy status and oxidation-reduction status in rat liver at high altitude (3.8 km)

Adult male rats were exposed to 3.8-km altitude for intervals ranging from 1 h-60 d. Liver samples were taken under light ether anesthesia and were examined by enzymatic analyses. Within 1-6 h of hypoxic exposure, ATP levels decreased while ADP and AMP levels increased, producing a fall in calculated ATP/ADP and adenylate charge ratios. Concurrently, lactate/pyruvate and alpha-glycerophosphate/dihydroxyacetone phosphate ratios increased markedly. Direct measurements of cellular pyridine nucleotides indicated increased NADH/NAD and NADPH/NADP ratios. Levels of total adenosine phosphate and pyridine nucleotides decreased in a significant accompanying response. Many metabolite levels and calculated ratios returned to near-normal values within 1 week of exposure, indicating secondary intracellular adjustments to hypoxic stress; however, persistence of that stress is reflected in lactate conentrations and both substrate redox ratios. Results support and explore concepts that increased oxidation-reduction status and decreased energy status are primary events during hypoxia.

Energy status and oxidation-reduction status in rat liver at high altitude (3.8 km)

Adult male rats were exposed to 3.8-km altitude for intervals ranging from 1 h-60 d. Liver samples were taken under light ether anesthesia and were examined by enzymatic analyses. Within 1-6 h of hypoxic exposure, ATP levels decreased while ADP and AMP levels increased, producing a fall in calculated ATP/ADP and adenylate charge ratios. Concurrently, lactate/pyruvate and alpha-glycerophosphate/dihydroxyacetone phosphate ratios increased markedly. Direct measurements of cellular pyridine nucleotides indicated increased NADH/NAD and NADPH/NADP ratios. Levels of total adenosine phosphates and pyridine nucleotides decreased in a significant accompanying response. Many metabolite levels and calculated ratios returned to near-normal values within 1 week of exposure, indicating secondary intracellular adjustments to hypoxic stress; however, persistence of that stress is reflected in lactate concentrations and both substrate redox ratios. Results support and explore concepts that increased oxidation-reduction status and decreased energy status are primary events during hypoxia.

Cell model for quantum fluids. III. Compressional waves in liquid hydrogen

The velocity of sound is calculated for each of the isotopic forms of liquid hydrogen using the quantum cell model. The velocity of sound increases as the pressure increases and decreases as the temperature increases. Also the reduced velocity of sound decreases as the value of the quantum parameter, Λ*, increases. In addition, the thermodynamic properties of liquid hydrogen compressed by a shock wave are calculated.