The main objective of this study is to determine the effects of APOL1 high-risk variants on the recipient’s kidney graft survival time, reported in standardized mean difference, and donor kidney function post kidney transplant.
- What is the pooled standardized mean difference (g) in graft survival time for APOL 1 low and high risk variants in donors and recipients?
- What is the pooled prevalence of APOL1 high-risk variant in ESKD, kidney transplant sub-population, kidney donors and graft recipients?
- What is the moderating effect of donors’ APOL1 high-risk variant on their kidney function post kidney donation?
- What is the moderating effect of donors’ APOL1 high-risk variant on recipients’ kidney allograft survival, in either low/high APOL1 risk types?
- What are the moderating effects of modifiable factors such race,age, gender, socio-economic status, forms of rejection, kidney function, HIV status, hypertension and other environmental factors on the recipient’s kidney allograft outcomes in donations from APOL1 high-risk variant donors?
This is a protocol for systematic review and meta-analysis of observational studies on APOL1 risk variants and kidney transplant. This protocol is designed to enable a reliable and accurate systematic review and meta-analysis on the impact of APOL1 risk variants on renal function of donor and recipient post-renal transplant. Using this protocol will enable determination of pooled effect sizes of graft survival (standardized mean difference, g) from donors with APOL1 high-risk variants, donors kidney function post organ donation and to assess suitability of including APOL1 risk variant status in the Kidney Donor Risk Index. There is no timeframe or restriction in selecting eligible studies using this protocol.
In addition to study design, inclusion and exclusion criteria will be applied in selecting eligible studies.
- Observational studies: Cohort studies, case controls, cross-sectional studies, historic cohort studies.
- Studies must report the primary outcome: Post-transplant graft survival time from APOL1 high-risk donor. Studies must be retrievable in the English Language.
- Reviews, editorials, interventional studies, commentaries, methodological articles, letters to editors, case reports
- Duplicates/ replicates of studies.
- Studies not retrievable in the English Language.
PICOs: The details for participants, intervention, comparison and outcomes (PICOs) are shown in Table 1.
This review will be reported in line with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2015 Statement).(27) The Protocol has the PRISMA-P Checklist attached as a supplementary material.
The search will use sensitive topic-based strategies designed for each database. The search will be carried out in the following databases: PUBMED, EMBASE, CINAHL, RESEARCHGATE, AJOL, GOOGLE SCHOLAR, WEB OF SCIENCE, SCOPUS and COCHRANE LIBRARY. Only observational studies will be included.
The search strategy includes MESH terms, text words and entry terms. Table 2 shows the search strategies as used in the PubMed. The same search strategy will be used in the other databases with slight modifications.
Data Extraction and Management
a. Data Extraction
Three main tools will be used for data extraction and management:
- a) Covidence software and b) Microsoft Excel c) CMA Version 3 Software
Six levels of data screening will be used for searched studies:
- Level 1 would involve screening of identified studies for the study design. Only observational studies, retrievable in the English Language would be selected.
- Level 2 will involve screening of studies in the titles and abstracts using entry terms, keywords and meSH terms.
- At Level 3, studies will be further screened for content by reading the full text article using the same search strategy.
- Level 4 will involve snowballing of literature on references from included studies.
- Level 5 will involve grey literature that report primary outcome and or secondary outcomes.
- Level 6, studies will be screened for outcomes, primary and secondary outcomes.
Eight reviewers are involved in this study. A pair of reviewers will independently screen the identified articles for eligibility using Covidence software.(28) The two reviewers will be blinded from each other using the screening tool. Conflict between the paired reviewers shall be resolved by a third reviewer who would will serve as a tie -breaker. The data of all screened studies will be deduplicated and exported to CMA version 3 for analysis.(29) Snowballing search of relevant studies through the review of the references of selected studies and grey literature will be performed manually.
b. Selection Process:
Agreement between two independent and blinded reviewers who screened titles, abstracts, full texts of eligible observational studies, snowballed articles and grey literature will form the basis for selecting studies for inclusion for systematic review and meta-analysis. Where there are conflicts in decision, this will be resolved by a third reviewer. Authors of eligible studies with any missing data will be contacted via email and telephone.
c. Data Collection Process:
Extractable data items from selected studies will include the following:
- The last name of the first author and the year of publication
- Sample size
- Survival time for kidney transplant from APOL1 high risk variant donors.
- Number of kidney donors with APOL1 high-risk variants
- Changes in donor’s eGFR/CKD stage before and after kidney donation
- Number of kidney transplant recipients with APOL1 high-risk variants
- Changes in recipient’s eGFR/CKD stage before and after kidney transplant
- The prevalence of the modifiable factors such as socio-demographics: race, age, gender and socio-economic status; hypertension, HIV status, forms of rejection and other environmental factors.
- The adjusted risk ratio of the modifiable factors besides APOL1 high-risk.
Data will be extracted into predefined forms created in MICROSOFT EXCEL.
Data items/Measurable outcomes
The measurable outcomes are
- Standardized mean difference, g in survival time of kidney transplants involving APOL1 high risk variant donors.
- Proportion of kidney transplant recipients with APOL1 high-risk variants
- The proportion of kidney transplant donors with APOL1 high-risk variants
- Changes in donor’s eGFR/CKD stage before and after kidney donation in relation to APOL1 risk variant status
- Changes in recipient’s eGFR/CKD stage before and after kidney transplant in relation to APOL1 risk variant status.
- The proportion of the modifiable factors besides APOL1 high-risk
- The adjusted risk ratio of the modifiable factors besides APOL1 high-risk variants.
The primary effect size is standardized mean difference, g.
Different primary indexes in individual studies of same design and report outcome will be converted to prevalence in the CMA Software.
Categorical outcomes: race, gender and socio-economic status; hypertension, HIV status, forms of rejection and other environmental factors, will be used for subgroup analysis.
Numerical outcomes such as age, kidney function variables will be used for meta-regression.
The criteria for data synthesis is a follows:
a. Studies that passed the methodological quality assessment using the NIH quality assessment tool for observational studies will be extracted. The results will be presented in tabular format.
b. in addition to a narrative synthesis, the following will be included in the meta-analysis:
1. Studies with primary outcome will be included for systematic review. The primary outcome is standardized mean difference (g) in recipients’ graft survival time for donations involving APOL1 high risk variant donors.
2. Studies with both primary and secondary outcomes will be included for meta-analysis.
c. Quantitative analysis
Criteria for Quantitative data Synthesis
Studies that are used in narrative synthesis, which also report both primary and secondary outcomes will be included for meta-analysis. Data items will be used to generate standardized mean difference, standard error, variance and 95% confidence interval. Heterogeneity will be assessed using the Q statistics and its p-value, tau2 and the Higgins I2. I² values of less than 40% will be considered low heterogeneity while values > 40 but < 75 % will be considered moderate and values > 75% are high. A random-effect model will be used for computation in this study. A sensitivity analysis will be performed to check for outlying studies and their effects on standardized mean difference, pooled mean and SD for changes in eGFR. Publication bias in the selection of studies will be visually assessed on the funnel plot (trim and fill method) and tested for asymmetry. Other statistical tests such as Egger’s regression intercept, Begg and Mazumdar's rank correlation and Orwin’s fail-safe N will be used where appropriate.
For each included study, the primary outcome which is the standardized mean difference (g) in recipient’s graft survival time for donations from APOL1 high risk variant donors will be used in calculating the pooled g value, standard error, variance and 95% CI of variance. This will be reported in forest plots.
Sub-group analysis will be performed using categorical data such as race, gender, socio-economic status, forms of rejection, hypertension, HIV status and any modifiable factor. All subgroup analysis will be presented in forest plots.
Meta-regression will be performed on quantitative explanatory variables such as changes in eGFR in donor and recipient before and after transplant, age and proteinuria (if quantified).
Quantitative analysis will be done using the Comprehensive Meta-Analysis (CMA) software version 3 (Biostat, USA).(29).
Risk of bias
The risk of bias will be assessed for each included study using the National Institute of Health (NIH) Quality assessment tool for observational cohort and cross-sectional studies. The NIH Quality assessment tool has 14 questions. Scores above 7 show good quality study with less bias. This will be cross-checked with the Cochrane tool of risk of bias assessment. Studies with extreme bias will be subjected to sensitivity testing using the include/exclude function in the CMA Software.
Assessment of Meta-bias
Meta-bias will be assessed as follows:
- Method of testing/reporting of APOL1 high-risk variants in kidney transplant recipients and donors. This will be done at outcome level.
- Reporting of study: Studies that were reported in different units but similar in outcome and design will be converted based on individual case evaluation. This will be evaluated for individual studies by assessing the unit of reporting of studies, for example, whether mean SD, prevalence with confidence intervals or incidence or proportion are reported. This is done at outcome level.
- Heterogeneity will be assessed at the study level using the Q statistics and its p-value, tau2 and the Higgins I2.
- Publication bias will be assessed at the study level using the funnel plot (trim and fill method) and test for asymmetry
- Sensitivity analysis will assessed at the study level using include and exclude function in the CMA Software
Presentation and Reporting of Results:
The study selection process will be summarized in a Prisma flow chart according to the PRISMA 2015 Statement and PRISMA-P Checklist. A table of the search strategy in various databases showing text words, MeSH and entry terms will be presented. List of included studies will be summarized in a table. Quantitative data such as standardized mean difference and pooled g, standard error and 95 % CI, p values, relative weights assigned to studies and heterogeneity tests will be included in the forest plots. A table of quality scores and risk of bias of each eligible study will be presented. Forest plots to show sub-group analysis will be included. Meta-regression and sensitivity analysis will be shown in figures and tables respectively.