Table 1.
Groups for meta-analysis.
Fig 1.
PRISMA 2020 flow diagram for new systematic review which includes searches of databases, registers and other sources.
Reference: Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ 2021;372:n71.doi: 10.1136/bmj.n71. For more information, visit: http://www.prisma-statement.org/.
Table 2.
Overview of included publications.
Fig 2.
Risk of bias assessment according to the QUADAS-2 tool for diagnostic test, based on four domains.
a) Summary for the 39 publications covering a comparison of preanalytical procedures. The results are weighted by the number of representative results for the 13 sub-categories included in the results. b) The risk-of-bias assessment for each of the four domains and the weighted percentage for each of the included publications.
Table 3.
Weighted contribution of included publications related to results of preanalytical procedures.
Fig 3.
Four critical steps were identified for the preanalytical procedure presented here with the number of included publications.
a) Blood drawing. b) Conditions before centrifugation. c) Conditions during centrifugation. d) Conditions after centrifugation.
Table 4.
Summary of findings and evidence grading.
Fig 4.
Random model meta-analysis of VEGF levels in healthy adults measured by ELISA assays from R&D Systems Inc.
Measurements below the calibration range as stated by the manufacturer are shown in the grey-shaded area. Means are calculated as standardized overall untransformed mean (MRAW) with 95% confidence. a) Sub-groups based on sample system with more than three values: whole blood, serum, activated plasma, EDTA- (including PECT and Edinburgh-plasma), heparin- and citrate-plasma (including, CTAD- and ACD-plasma). b) Sub-analysis was performed for publications using different anticoagulants for plasma: EDTA, heparin, citrate, CTAD, ACD (not included, n = 1), Edinburgh (not included, n = 1) and PECT (not included, n = 2).