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M.S.Y. Ng et al.
plots with ten or less studies have insufficient power to identify heterogeneity.17 Sensitivity analyses were completed by calcu- lating the adjusted OR for each geographical location (the Americas, Europe, other) and patient subgroup (cardiac surgery, intensive care unit (ICU), other). Time-lapse analyses involved adding studies sequentially to the random effects model in order of the recruitment period (i.e., from 1980-2011).
In the extremes analyses for in-hospital mortality and nosoco- mial infection, logistic regression was used to calculate an aggre- gate OR and 95% CI comparing patients transfused with mean PRBC aged less than ten days to those transfused with mean PRBC aged at least 30 days old. The ten day threshold for fresh PRBC was selected to align with the Red Cell Storage Duration Study (RECESS). The 30 day threshold for stored PRBC was selected to maintain relevance for jurisdictions which store PRBC for 35 (e.g., China, The Netherlands, UK) and 42 days (e.g., Australia, USA, Canada). Furthermore, in vitro research sug- gests that PRBC storage lesions become clinically significant up to day 28.18 Subgroup analyses were completed to measure the modifying effects of leukoreduction status. Zero-inflated Poisson regression was used to calculate an aggregate IRR and 95% CI for HLOS extremes analysis. Age, sex and PRBC volume were included as covariates for each model. STATATM (StataCorp 2017, version 15.0) was utilized for all analyses.
Results
Study characteristics
Using the search strategy as previously specified, 3285 abstracts were retrieved from PubMed and EMBASE (Figure 1).5 After two sequential screens and a manual search, 64 clinical studies investigating clinical outcomes associated with PRBC storage duration were retained. Eight RCTs were removed, leaving 56 observational stud- ies. Sixteen datasets were received from 14 investigators between January 2014 and January 2017. These studies covered 17,967 patients across burns, general surgery, ICU, oncology, acute medicine, trauma and cardiac sur- gery cohorts (Table 2). Overall, 77,962 units of PRBC were transfused across 16 studies with an average of 4.34 units transfused per patient. 8.1% of patients received more than ten units of PRBCs. The mean PRBC age transfused was less than ten days in 15.4% and at least 30 days in 18.9% of participants. The mean age of patients was 57.82, with 45.3% of patients being older than 65.
On paper level comparisons, included studies had simi- lar recruitment dates, mean sample size (n=904.56 versus n=1003.53) and rates of positive mortality findings (36.36% versus 33.33%) compared to studies for which
Figure 1. Outline of study selection. Fifty- six observational studies investigated the effects of PRBC storage duration on clini- cal outcomes, such as mortality, infection risk and hospital length of stay. Forty datasets were unavailable for various rea- sons: (1) no response from corresponding author after initial email, (2) lack of corre- spondence after initial contact, (3) institu- tional policy against data use by external investigators, (4) insufficient staff avail- able to access data on site, (5) investiga- tor retracted participation in study, and (6) other (e.g., data file corrupted). PRBC: packed red blood cells; yo: years old: RCT: randomized controlled trials.
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haematologica | 2018; 103(9)