Does advance contact with research participants increase response to questionnaires: an updated systematic review and meta-analysis

Abstract Background Questionnaires remain one of the most common forms of data collection in epidemiology, psychology and other human-sciences. However, results can be badly affected by non-response. One way to potentially reduce non-response is by sending potential study participants advance communication. The last systematic review to examine the effect of questionnaire pre-notification on response is 10 years old, and lacked a risk of bias assessment. Objectives Update the section of the Cochrane systematic review, Edwards et al. (2009), on pre-notification to include 1) recently published studies, 2) an assessment of risk of bias, 3) Explore if heterogeneity is reduced by: delay between pre-contact and questionnaire delivery, the method of pre-contact, if pre-contact and questionnaire delivery differ, if the pre-contact includes a foot-in-the-door manipulation, and study’s the risk of bias. Methods Inclusion criteria: population: any population, intervention: comparison of some type of pre-notification, comparison group: no pre-notification, outcome: response rates. Study design: randomised controlled trails. Exclusion criteria: NA. Data sources: Studies which cited or were included in Edwards et al. (2009); We additionally searched: CINAHL, Web of Science, PsycInfo, MEDLINE, EconLit, EMBASE, Cochrane Central, Cochrane CMR, ERIC, and Sociological Abstracts. The searches were implemented in June 2018 and May 2021. Study screening: a single reviewer screened studies, with a random 10% sample independently screened to ascertain accuracy. Data extraction: data was extracted by a single reviewer twice, with a week between each extraction. Risk of Bias: within studies bias was assessed using the Cochrane Risk of Bias tool (ROB1) by a single unblinded reviewer, across studies bias was assessed using funnel plots. Synthesis Method: study results were meta-analysed with a random effects model using the final response rate as the outcome. Evaluation of Uncertainty: Uncertainty was evaluated using the GRADE approach. Results One hundred seven trials were included with 211,802 participants. Over-all pre-notification increased response, OR = 1.33 (95% CI: 1.20–1.47). However, there was a large amount of heterogeneity (I2 = 97.1%), which was not explained by the subgroup analyses. In addition, when studies at high or unclear risk of bias were excluded the effect was to reduced OR = 1.09 (95% CI: 0.99–1.20). Because of the large amount of heterogeneity, even after restricting to low risk of bias studies, there is still moderate uncertainty in these results. Conclusions Using the GRADE evaluation, this review finds moderate evidence that pre-notification may not have an effect on response rates. Funding Economic and Social Research Council. Preregistration None.

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The effect of preoperative stoma site marking on risk of stoma-related complications in patients with intestinal ostomy—protocol of a systematic review and meta-analysis

Systematic Reviews ◽

10.1186/s13643-021-01684-8 ◽

2021 ◽

Vol 10 (1) ◽

Author(s):

Charlotte Mareike Kugler ◽

Jessica Breuing ◽

Tanja Rombey ◽

Simone Hess ◽

Peter Ambe ◽

...

Keyword(s):

Quality Of Life ◽

Systematic Review ◽

Data Extraction ◽

Meta Analysis ◽

Risk Of Bias ◽

Stoma Site ◽

Preoperative Marking ◽

Stoma Site Marking ◽

Randomised Controlled

Abstract Background An intestinal ostomy is an artificial bowel opening created on the skin. Procedure-related mortality is extremely rare. However, the presence of an ostomy may be associated with significant morbidity. Complications negatively affect the quality of life of ostomates. Preoperative stoma site marking can reduce stoma-related complications and is recommended by several guidelines. However, there is no consensus on the procedure and recommendations are based on low-quality evidence. The objective of the systematic review will be to investigate if preoperative stoma site marking compared to no preoperative marking in patients undergoing intestinal stoma surgery reduces or prevents the rate of stoma-related complications. Methods We will include (cluster-) randomised controlled trials and cohort studies that involve patients with intestinal ostomies comparing preoperative stoma site marking to no preoperative marking and report at least one patient-relevant outcome. For study identification, we will systematically search MEDLINE/PubMed, EMBASE, CENTRAL and CINHAL as well as Google Scholar, trial registries, conference proceedings and reference lists. Additionally, we will contact experts in the field. Two reviewers will independently perform study selection and data extraction. Outcomes will be prioritised based on findings from telephone interviews with five ostomates and five ostomy and wound nurses prior to conducting the review. Outcomes may include but are not limited to stoma-related complications (infection, parastomal abscess, hernia, mucocutaneous separation, dermatological complications, stoma necrosis, stenosis, retraction and prolapse) or other patient-relevant postoperative endpoints (quality of life, revision rate, dependence on professional care, mortality, length of stay and readmission). We will use the ROBINS-I or the Cochrane risk of bias tool to assess the risk of bias of the included studies. We will perform a meta-analysis and assess the certainty of evidence using the GRADE approach. Discussion With the results of the systematic review, we aim to provide information for future clinical guidelines and influence clinical routine with regard to preoperative stoma site marking in patients undergoing ostomy surgery. When the evidence of our systematic review is low, it would still be a useful basis for future clinical trials by identifying data gaps. Systematic review registration PROSPERO registration number: CRD42021226647

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Microbial colonisation associated with conventional and self-ligating brackets: a systematic review

Journal of Orthodontics ◽

10.1177/14653125211056023 ◽

2021 ◽

pp. 146531252110560

Author(s):

Nidhi P Parmar ◽

Gabrielle L Thompson ◽

Nikki E Atack ◽

Anthony J Ireland ◽

Martyn Sherriff ◽

...

Keyword(s):

Systematic Review ◽

Randomised Controlled Trials ◽

Data Extraction ◽

Meta Analysis ◽

Risk Of Bias ◽

Controlled Trials ◽

Significant Difference ◽

Critical Appraisal Skills ◽

Randomised Controlled ◽

Bracket Design

Background: Decalcification and gingivitis caused by plaque accumulation around brackets are common iatrogenic effects of fixed appliances. The influence of conventional versus self-ligating bracket design on microbial colonisation is unknown. Objective: To assess the levels of microbial colonisation associated with conventional and self-ligating brackets. Search sources: Three databases were searched for publications from 2009 to 2021. Data selection: Randomised controlled trials comparing levels of microbial colonisation before and during treatment with conventional and self-ligating brackets were assessed independently and in duplicate. Data extraction: Data were extracted independently by two authors from the studies that fulfilled the inclusion criteria. Risk of bias assessments were made using the revised Cochrane risk of bias tool for randomized trials. The quality of the included studies was assessed using the Critical Appraisal Skills Programme Checklist. Results: A total of 11 randomised controlled trials were included in this systematic review. Six of the studies were found to be at low risk of bias and five presented with some concerns. The studies were considered moderate to high quality. Five trials reported no statistically significant difference in microbial colonisation between bracket types. The remaining studies showed mixed results, with some reporting increased colonisation of conventional brackets and others increased colonisation of self-ligating brackets. The heterogeneity of study methods and outcomes precluded meta-analysis. Conclusion: Of the 11 studies included in this systematic review, five found no differences in colonisation between conventional and self-ligating brackets. The remaining studies showed mixed results. The evidence is inconclusive regarding the association between bracket design and levels of microbial colonisation.

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Prevalence of retinopathy in prediabetes: protocol for a systematic review and meta-analysis

BMJ Open ◽

10.1136/bmjopen-2020-040997 ◽

2021 ◽

Vol 11 (1) ◽

pp. e040997

Author(s):

Varo Kirthi ◽

Paul Nderitu ◽

Uazman Alam ◽

Jennifer Evans ◽

Sarah Nevitt ◽

...

Keyword(s):

Systematic Review ◽

Diabetic Retinopathy ◽

Data Extraction ◽

Meta Analysis ◽

International Diabetes Federation ◽

Current Data ◽

Risk Of Bias ◽

Fundus Photography ◽

Primary Data ◽

Cochrane Library

IntroductionThere is growing evidence of a higher than expected prevalence of retinopathy in prediabetes. This paper presents the protocol of a systematic review and meta-analysis of retinopathy in prediabetes. The aim of the review is to estimate the prevalence of retinopathy in prediabetes and to summarise the current data.Methods and analysisThis protocol is developed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) guidelines. A comprehensive electronic bibliographic search will be conducted in MEDLINE, EMBASE, Web of Science, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Google Scholar and the Cochrane Library. Eligible studies will report prevalence data for retinopathy on fundus photography in adults with prediabetes. No time restrictions will be placed on the date of publication. Screening for eligible studies and data extraction will be conducted by two reviewers independently, using predefined inclusion criteria and prepiloted data extraction forms. Disagreements between the reviewers will be resolved by discussion, and if required, a third (senior) reviewer will arbitrate.The primary outcome is the prevalence of any standard features of diabetic retinopathy (DR) on fundus photography, as per International Clinical Diabetic Retinopathy Severity Scale (ICDRSS) classification. Secondary outcomes are the prevalence of (1) any retinal microvascular abnormalities on fundus photography that are not standard features of DR as per ICDRSS classification and (2) any macular microvascular abnormalities on fundus photography, including but not limited to the presence of macular exudates, microaneurysms and haemorrhages. Risk of bias for included studies will be assessed using a validated risk of bias tool for prevalence studies. Pooled estimates for the prespecified outcomes of interest will be calculated using random effects meta-analytic techniques. Heterogeneity will be assessed using the I2 statistic.Ethics and disseminationEthical approval is not required as this is a protocol for a systematic review and no primary data are to be collected. Findings will be disseminated through peer-reviewed publications and presentations at national and international meetings including Diabetes UK, European Association for the Study of Diabetes, American Diabetes Association and International Diabetes Federation conferences.PROSPERO registration numberCRD42020184820.

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Effectiveness of Antalgic Therapies in Patients with Vertebral Bone Metastasis: A Protocol for a Systematic Review and Meta-Analysis

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph18083991 ◽

2021 ◽

Vol 18 (8) ◽

pp. 3991

Author(s):

Antonio Jose Martin-Perez ◽

María Fernández-González ◽

Paula Postigo-Martin ◽

Marc Sampedro Pilegaard ◽

Carolina Fernández-Lao ◽

...

Keyword(s):

Systematic Review ◽

Bone Metastasis ◽

Data Extraction ◽

Meta Analysis ◽

Risk Of Bias ◽

Cochrane Library ◽

Pharmacological Intervention ◽

Vertebral Metastasis ◽

Randomized Controlled Clinical Trials

There is no systematic review that has identified existing studies evaluating the pharmacological and non-pharmacological intervention for pain management in patients with bone metastasis. To fill this gap in the literature, this systematic review with meta-analysis aims to evaluate the effectiveness of different antalgic therapies (pharmacological and non-pharmacological) in the improvement of pain of these patients. To this end, this protocol has been written according to the Preferred Reporting Items for Systematic review and Meta-Analysis Protocols (PRISMA-P) and registered in PROSPERO (CRD42020135762). A systematic search will be carried out in four international databases: Medline (Via PubMed), Web of Science, Cochrane Library and SCOPUS, to select the randomized controlled clinical trials. The Risk of Bias Tool developed by Cochrane will be used to assess the risk of bias and the quality of the identified studies. A narrative synthesis will be used to describe and compare the studies, and after the data extraction, random effects model and a subgroup analyses will be performed according to the type of intervention, if possible. This protocol aims to generate a systematic review that compiles and synthesizes the best and most recent evidence on the treatment of pain derived from vertebral metastasis.

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Comparative efficacy and safety of interventions for treating head lice: a protocol for systematic review and network meta-analysis

BMJ Paediatrics Open ◽

10.1136/bmjpo-2021-001129 ◽

2021 ◽

Vol 5 (1) ◽

pp. e001129

Author(s):

Bill Stevenson ◽

Wubshet Tesfaye ◽

Julia Christenson ◽

Cynthia Mathew ◽

Solomon Abrha ◽

...

Keyword(s):

Systematic Review ◽

Randomised Controlled Trials ◽

Meta Analysis ◽

Grey Literature ◽

Risk Of Bias ◽

Controlled Trials ◽

Head Lice ◽

Efficacy And Safety ◽

Randomised Controlled ◽

Meta Analyses

BackgroundHead lice infestation is a major public health problem around the globe. Its treatment is challenging due to product failures resulting from rapidly emerging resistance to existing treatments, incorrect treatment applications and misdiagnosis. Various head lice treatments with different mechanism of action have been developed and explored over the years, with limited report on systematic assessments of their efficacy and safety. This work aims to present a robust evidence summarising the interventions used in head lice.MethodThis is a systematic review and network meta-analysis which will be reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses statement for network meta-analyses. Selected databases, including PubMed, Embase, MEDLINE, Web of Science, CINAHL and Cochrane Central Register of Controlled Trials will be systematically searched for randomised controlled trials exploring head lice treatments. Searches will be limited to trials published in English from database inception till 2021. Grey literature will be identified through Open Grey, AHRQ, Grey Literature Report, Grey Matters, ClinicalTrials.gov, WHO International Clinical Trials Registry and International Standard Randomised Controlled Trials Number registry. Additional studies will be sought from reference lists of included studies. Study screening, selection, data extraction and assessment of methodological quality will be undertaken by two independent reviewers, with disagreements resolved via a third reviewer. The primary outcome measure is the relative risk of cure at 7 and 14 days postinitial treatment. Secondary outcome measures may include adverse drug events, ovicidal activity, treatment compliance and acceptability, and reinfestation. Information from direct and indirect evidence will be used to generate the effect sizes (relative risk) to compare the efficacy and safety of individual head lice treatments against a common comparator (placebo and/or permethrin). Risk of bias assessment will be undertaken by two independent reviewers using the Cochrane Risk of Bias tool and the certainty of evidence assessed using the Grading of Recommendations, Assessment, Development and Evaluations guideline for network meta-analysis. All quantitative analyses will be conducted using STATA V.16.DiscussionThe evidence generated from this systematic review and meta-analysis is intended for use in evidence-driven treatment of head lice infestations and will be instrumental in informing health professionals, public health practitioners and policy-makers.PROSPERO registration numberCRD42017073375.

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Effects of open-label placebos in clinical trials: a systematic review and meta-analysis

Scientific Reports ◽

10.1038/s41598-021-83148-6 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Melina von Wernsdorff ◽

Martin Loef ◽

Brunna Tuschen-Caffier ◽

Stefan Schmidt

Keyword(s):

Systematic Review ◽

Clinical Trials ◽

Medical Condition ◽

Data Extraction ◽

Meta Analysis ◽

Risk Of Bias ◽

Open Label ◽

Cancer Related Fatigue ◽

Promising Treatment ◽

Irritable Bowel

AbstractOpen-label placebos (OLPs) are placebos without deception in the sense that patients know that they are receiving a placebo. The objective of our study is to systematically review and analyze the effect of OLPs in comparison to no treatment in clinical trials. A systematic literature search was carried out in February 2020. Randomized controlled trials of any medical condition or mental disorder comparing OLPs to no treatment were included. Data extraction and risk of bias rating were independently assessed. 1246 records were screened and thirteen studies were included into the systematic review. Eleven trials were eligible for meta-analysis. These trials assessed effects of OLPs on back pain, cancer-related fatigue, attention deficit hyperactivity disorder, allergic rhinitis, major depression, irritable bowel syndrome and menopausal hot flushes. Risk of bias was moderate among all studies. We found a significant overall effect (standardized mean difference = 0.72, 95% Cl 0.39–1.05, p < 0.0001, I2 = 76%) of OLP. Thus, OLPs appear to be a promising treatment in different conditions but the respective research is in its infancy. More research is needed, especially with respect to different medical and mental disorders and instructions accompanying the OLP administration as well as the role of expectations and mindsets.

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Clinical effectiveness of convalescent plasma in hospitalized patients with COVID-19: a systematic review and meta-analysis

Therapeutic Advances in Respiratory Disease ◽

10.1177/17534666211028077 ◽

2021 ◽

Vol 15 ◽

pp. 175346662110280

Author(s):

Roberto Ariel Abeldaño Zuñiga ◽

Ruth Ana María González-Villoria ◽

María Vanesa Elizondo ◽

Anel Yaneli Nicolás Osorio ◽

David Gómez Martínez ◽

...

Keyword(s):

Systematic Review ◽

Clinical Trials ◽

Clinical Improvement ◽

Data Extraction ◽

Meta Analysis ◽

Clinical Effectiveness ◽

Risk Of Bias ◽

Hospitalized Patients ◽

Low Risk ◽

Controlled Clinical Trials

Aims: Given the variability of previously reported results, this systematic review aims to determine the clinical effectiveness of convalescent plasma employed in the treatment of hospitalized patients diagnosed with COVID-19. Methods: We conducted a systematic review of controlled clinical trials assessing treatment with convalescent plasma for hospitalized patients diagnosed with SARS-CoV-2 infection. The outcomes were mortality, clinical improvement, and ventilation requirement. Results: A total of 51 studies were retrieved from the databases. Five articles were finally included in the data extraction and qualitative and quantitative synthesis of results. The overall risk of bias in the reviewed articles was established at low-risk only in two trials. The meta-analysis suggests that there is no benefit of convalescent plasma compared with standard care or placebo in reducing the overall mortality and the ventilation requirement. However, there could be a benefit for the clinical improvement in patients treated with plasma. Conclusion: Current results led to assume that the convalescent plasma transfusion cannot reduce the mortality or ventilation requirement in hospitalized patients diagnosed with SARS-CoV-2 infection. More controlled clinical trials conducted with methodologies that ensure a low risk of bias are still needed. The reviews of this paper are available via the supplemental material section.

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Racecadotril for acute diarrhoea in children: systematic review and meta-analyses

Archives of Disease in Childhood ◽

10.1136/archdischild-2015-309676 ◽

2015 ◽

Vol 101 (3) ◽

pp. 234-240 ◽

Cited By ~ 14

Author(s):

Morris Gordon ◽

Anthony Akobeng

Keyword(s):

Systematic Review ◽

Adverse Events ◽

Methodological Quality ◽

Data Extraction ◽

Meta Analysis ◽

Acute Diarrhoea ◽

Risk Of Bias ◽

Duration Of Symptoms ◽

Duration Of Illness ◽

Significant Difference

ObjectiveRacecadotril is an antisecretory agent that can prevent fluid/electrolyte depletion from the bowel as a result of acute diarrhoea without affecting intestinal motility. An up-to-date systematic review is indicated to summarise the evidence on racecadotril for the treatment of acute diarrhoea in children.DesignA Cochrane format systematic review of randomised controlled trials (RCTs). Data extraction and assessment of methodological quality were performed independently by two reviewers. Methodological quality was assessed using the Cochrane risk of bias tool.PatientsChildren with acute diarrhoea, as defined by the primary studies.InterventionsRCTs comparing racecadotril with placebo or other interventions.Main outcome measursDuration of illness, stool output/volume and adverse events.ResultsSeven RCTs were included, five comparing racecadotril with placebo or no intervention, one with pectin/kaolin and one with loperamide. Moderate to high risk of bias was present in all studies. There was no significant difference in efficacy or adverse events between racecadotril and loperamide. A meta-analysis of three studies with 642 participants showed significantly shorter duration of symptoms with racecadotril compared with placebo (mean difference −53.48 h, 95% CI −65.64 to −41.33). A meta-analysis of five studies with 949 participants showed no significant difference in adverse events between racecadotril and placebo (risk ratio 0.99, 95% CI 0.73 to 1.34).ConclusionsThere is some evidence that racecadotril is more effective than placebo or no intervention in reducing the duration of illness and stool output in children with acute diarrhoea. However, the overall quality of the evidence is limited due to sparse data, heterogeneity and risk of bias. Racecadotril appears to be safe and well tolerated.

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Effectiveness and safety of herbal medicines for induction of labour: a systematic review and meta-analysis

BMJ Open ◽

10.1136/bmjopen-2018-022499 ◽

2018 ◽

Vol 8 (10) ◽

pp. e022499 ◽

Cited By ~ 8

Author(s):

Collins Zamawe ◽

Carina King ◽

Hannah Maria Jennings ◽

Chrispin Mandiwa ◽

Edward Fottrell

Keyword(s):

Systematic Review ◽

Data Extraction ◽

Meta Analysis ◽

Experimental Studies ◽

Herbal Medicines ◽

Risk Of Bias ◽

Induction Of Labour ◽

Quality Data ◽

Eligibility Criteria ◽

Significant Difference

ObjectiveThe use of herbal medicines for induction of labour (IOL) is common globally and yet its effects are not well understood. We assessed the efficacy and safety of herbal medicines for IOL.DesignSystematic review and meta-analysis of published literature.Data sourcesWe searched in MEDLINE, AMED and CINAHL in April 2017, updated in June 2018.Eligibility criteriaWe considered experimental and non-experimental studies that compared relevant pregnancy outcomes between users and non-user of herbal medicines for IOL.Data extraction and synthesisData were extracted by two reviewers using a standardised form. A random-effects model was used to synthesise effects sizes and heterogeneity was explored through I2statistic. The risk of bias was assessed using ‘John Hopkins Nursing School Critical Appraisal Tool’ and ‘Cochrane Risk of Bias Tool’.ResultsA total of 1421 papers were identified through the searches, but only 10 were retained after eligibility and risk of bias assessments. The users of herbal medicine for IOL were significantly more likely to give birth within 24 hours than non-users (Risk Ratio (RR) 4.48; 95% CI 1.75 to 11.44). No significant difference in the incidence of caesarean section (RR 1.19; 95% CI 0.76 to 1.86), assisted vaginal delivery (RR 0.73; 95% CI 0.47 to 1.14), haemorrhage (RR 0.84; 95% CI 0.44 to 1.60), meconium-stained liquor (RR 1.20; 95% CI 0.65 to 2.23) and admission to nursery (RR 1.08; 95% CI 0.49 to 2.38) was found between users and non-users of herbal medicines for IOL.ConclusionsThe findings suggest that herbal medicines for IOL are effective, but there is inconclusive evidence of safety due to lack of good quality data. Thus, the use of herbal medicines for IOL should be avoided until safety issues are clarified. More studies are recommended to establish the safety of herbal medicines.

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Genetic Association Studies of Red Blood Cell Transfusion Related Alloimmunization: A Systematic Review and Meta-Analysis

Blood ◽

10.1182/blood-2019-128199 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 2459-2459

Author(s):

Jorn Gerritsma ◽

Ilja Oomen ◽

Sanne Meinderts ◽

C. Ellen van der Schoot ◽

Bart J. Biemond ◽

...

Keyword(s):

Systematic Review ◽

Genetic Variants ◽

Screening Tool ◽

Association Studies ◽

Data Extraction ◽

Meta Analysis ◽

Genetic Association Studies ◽

Risk Of Bias ◽

Cell Disease

Introduction: Blood transfusions are an important treatment modality for patients with either acute or chronic onset anemia such as trauma, sickle cell disease, and hematological malignancies. Transfusion poses a risk for alloimmunization, which may lead to potentially lethal transfusion reactions. A promising strategy to prevent alloimmunization is extensive matching on blood groups, yet this is a costly procedure and should be reserved for patients at highest risk for alloimmunization. Identification of genetic variants that increase the risk for alloimmunization might help to identify high-risk patients and could be used as a screening tool for patients receiving multiple transfusions. Objectives: To summarize all available evidence on genetic risk factors for alloimmunization after blood transfusion. Design: Systematic review with meta-analysis of observational studies. Studies were only included in the meta-analysis if polymorphisms were tested at least 3 times, and if ethnic background of the population and the control populations were comparable between studies. Data sources: The online databases Embase, MEDLINE and the Cochrane Library were search for relevant articles with search terms: 1) transfusion, 2) alloimmunization 3) genetics. The search was last updated March 2018. Eligibility criteria: 1) Primary study that assessed the association of genetic polymorphisms with transfusion related alloimmunization, 2) a human population, 3) studies with at least 50 patients, 4) full text availability. Data extraction: Two reviewers independently screened articles for eligibility, extracted data using a standardized data extraction form. Extracted data included study setting, study population, participant demographics, baseline characteristics, study methodology, comparisons and outcome, and risk of bias. Primary outcome measure: Alloimmunization after one or more blood transfusions. Risk of bias assessment: The quality of the included studies was assessed by the Q-genie tool for genetic association studies. Results: A total of 2045 cases and 24084 controls were derived from 18 genetic case-control studies that were included in this systematic review. Most commonly studied disease group was sickle cell disease (SCD) (8 studies). Three studies included patients with different diseases and seven studies did not report the underlying disease. Eleven studies identified the association of HLA polymorphisms with alloimmunization and 8 studies focused on non-HLA variants. Overall quality of the included studies was moderate (11 studies), 2 studies were of high quality, and 5 studies were ranked as poor. HLA-DRB1*04 (Odds Ratio 7.16, 95%CI 3.87-13.22, P<0.00001) and HLA-DRB1*15 (OR 3.01, 95%CI 1.84-5.53, P<0.0001) were by meta-analysis significantly associated with anti-Fy(a) formation, although there was considerable heterogeneity (I2=78% and 55% respectively). Moreover, HLA-DRB1*10 (OR 2.64, 95%CI 1.41-4.95, P=0.002), HLA*DRB1*11 (OR 2.11, 95%CI 1.34-3.32, P=0.001), and HLA-DRB1*13 (OR 1.71, 95%CI 1.26-2.33, P=0.0006) were overall associated with anti-Kell formation. Heterogeneity was less prominent with an I2 of 0%, 54% and 19% respectively (Figure 1). No other variants were eligible for meta-analysis. Non-HLA variants were tested less extensively, as most variants were reported by only 1 study. Polymorphisms of genes in the immunomodulatory pathways were assessed most frequently. Of these variants, FC-gamma-receptor 2C.nc-ORF was associated with a decreased risk of alloimmunization in SCD (OR 0.26, 95%CI 0.11-0.64, p=0.003). All other associations that were described as significant by the original articles were summarized in Figure 2. Discussion: There is limited evidence supporting the role of genetic risk factors for alloimmunization. The results of our meta-analysis suggest that several HLA polymorphisms potentially influence antigen presentation of the Duffy(a) and Kell antigen. Once confirmed by experimental studies, these polymorphisms could be used as a screening tool for the prevention of alloimmunization among frequently transfused patients. Overall, the effect of genetic variants on alloimmunization has mostly been assessed by small studies, hampering reliable interpretation of the results. Future studies should include large and well-defined cohorts when performing genetic analysis on this complicated subject. Disclosures No relevant conflicts of interest to declare.

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