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Wet- versus dry-suction techniques for EUS-FNA of solid lesions: A systematic review and meta-analysis

1 Department of Internal Medicine, The Brooklyn Hospital Center, Brooklyn, New York, USA
2 Department of Internal Medicine, Mather Hospital, Port Jefferson, New York, USA
3 Langone Health, Inflammatory Bowel Disease Center, New York University, New York, USA; Department of Gastroenterology, School of Medicine, Marmara University, Istanbul, Turkey
4 Division of Gastroenterology, The Brooklyn Hospital Center, Brooklyn, New York, USA
5 Division of Gastroenterology and Hepatology, CHI Health Creighton University Medical Center, Omaha, Nebraska, USA
6 Division of Gastroenterology, Stanford University, Stanford, California, USA
7 Division of Gastroenterology, Rush University Medical Center, Chicago, Illinois, USA
8 Gastroenterology and Hepatology, University of Nebraska Medical Center, Omaha, Nebraska, USA
9 Division of Gastroenterology, Moffitt Cancer Center, University of South Florida, Tampa, Florida, USA
10 Department of Medical Sciences, Section of Gastroenterology, University of Foggia, 71122 Foggia, Italy
11 Center for Advanced Therapeutic Endoscopy (CATE), Centura Health, Porter Hospital, Peak Gastroenterology, Denver, Colorado, USA

Date of Submission24-Sep-2020
Date of Acceptance21-Mar-2021
Date of Web Publication08-Jul-2021

Correspondence Address:
Douglas G Adler,
Porter Adventist Hospital 2525 S Downing St, Denver, CO 80210
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/EUS-D-20-00198

PMID: 34259217


The optimal sampling techniques for EUS-FNA remain unclear and have not been standardized. To improve diagnostic accuracy, suction techniques for EUS-FNA have been developed and are widely used among endoscopists. The aim of this study was to compare wet-suction and dry-suction EUS-FNA techniques for sampling solid lesions. We performed a comprehensive literature search of major databases (from inception to June 2020) to identify prospective studies comparing wet-suction EUS-FNA and dry-suction EUS-FNA. Specimen adequacy, sample contamination, and histologic accuracy were assessed by pooling data using a random-effects model expressed in terms of odds ratio (OR) and 95% confidence interval (CI). Six studies including a total of 418 patients (365 wet suction vs. 377 dry suction) were included in our final analysis. The study included a total of 535 lesions (332 pancreatic lesions and 203 nonpancreatic lesions). The pooled odds of sample adequacy was 3.18 (CI: 1.82–5.54, P = 0.001) comparing wet- and dry-suction cohorts. The pooled odds of blood contamination was 1.18 (CI: 0.75–1.86, P = 0.1). The pooled rate for blood contamination was 58.33% (CI: 53.65%–62.90%) in the wet-suction cohort and 54.60% (CI 49.90%– 59.24%) in the dry-suction cohort (P = 0.256). The pooled odds of histological diagnosis was 3.68 (CI 0.82–16.42, P = 0.1). Very few adverse events were observed and did not have an impact on patient outcomes using either method. EUS-FNA using the wet-suction technique offers higher specimen quality through comparable rates of blood contamination and histological accuracy compared to dry-suction EUS-FNA.

Keywords: dry suction, EUS, FNA, solid lesions, wet suction

How to cite this URL:
Ramai D, Singh J, Kani T, Barakat M, Chandan S, Brooks OW, Ofosu A, Khan SR, Dhindsa B, Dhaliwal A, Quintero EJ, Cheung D, Facciorusso A, McDonough S, Adler DG. Wet- versus dry-suction techniques for EUS-FNA of solid lesions: A systematic review and meta-analysis. Endosc Ultrasound [Epub ahead of print] [cited 2021 Oct 16]. Available from: http://www.eusjournal.com/preprintarticle.asp?id=320792

  Introduction Top

Tissue acquisition using EUS-FNA was first introduced 25 years ago and has become an important part of the diagnostic and staging algorithm for both benign and malignant diseases of the GI tract.[1] As such, various suction techniques for EUS-FNA have been developed to improve diagnostic accuracy. To this end, the dry- and wet-suction techniques have been proposed as methods for tissue acquisition using EUS-FNA.

The dry-suction or traditional technique involves removal of the stylet and the use of a 10 ml prevacuum syringe to generate negative pressure to aid in the acquisition of tissue specimen. However, this technique has associated flaws which may impact the quality of the aspirate.[2],[3] This technique has been shown to increase the cellularity of a sample but also increases the chance of blood contamination.[4]

Alternatively, the wet-suction technique involves the use of saline or heparin to preflush the needle prior to aspiration.[5],[6] Prior to puncturing the lesion, the stylet is removed and the needle is preflushed with about 5 ml of liquid. Left attached to the proximal port and later used for aspiration is a 10 ml syringe prefilled with 3 ml of liquid. Once the needle is passed into the lesion, the needle is moved back and forth roughly three times and suctioned to acquire tissue aspirate. This is repeated about four times prior to air flushing the sample onto a slide for review.

Compared to dry-suction EUS-FNA, the wet-suction technique has been shown to increase cellularity and adequacy of specimens without adding blood contamination.[7] To this end, we conducted a systematic review and meta-analysis to evaluate the differences between wet- and dry-suction techniques for the sampling of solid lesions.

  Methods Top

Search strategy

We conducted a comprehensive search of several databases and conference proceedings including PubMed, EMBASE, and Google-Scholar databases to April 2020. An experienced medical librarian using inputs from the study authors helped with the literature search. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines using a predefined protocol to identify studies reporting the use of wet suction and dry suction during EUS FNA [Supplementary Table 1 [Additional file 1]].[8],[9]

Keywords used in the literature search included a combination of “endoscopic ultrasound“, “fine needle aspiration“, “FNA,” “dry-suction“, “wet-suction” “pancreatic mass“, and “solid lesions.” The search was restricted to studies performed on human subjects and published in the English language in peer-reviewed journals [Supplementary Table 2 [Additional file 2]]. Two authors (DR and JS) independently reviewed the title and abstract of studies identified in the primary search and excluded studies that did not address the research question, based on prespecified exclusion and inclusion criteria. The full text of the remaining articles was reviewed to determine whether it contained relevant information. Any discrepancy in article selection was resolved by consensus and in discussion with a co-author.

The bibliographic section of the selected articles, as well as the systematic and narrative articles on the topic, was manually searched for additional relevant articles.

Study selection

We included comparative studies that evaluated and compared wet-suction and dry-suction techniques for EUS FNA. Studies irrespective of the sample size, inpatient/outpatient setting, and geography were included as long as they provided data needed for the analysis.

Inclusion criteria were (1) comparative studies. Exclusion criteria included (1) pediatric (age <18 years) studies, (2) case reports or case series with less than 10 patients, and (3) studies not published in the English language. In the event of multiple publications from the same cohort and/or overlapping cohorts, data from the most recent and/or most appropriate comprehensive report were retained.

Data abstraction and quality assessment

Study references and citations were collected in EndNote X9 (Thomson Reuters, New York, NY). Covidence systematic review software (Veritas Health Innovation, Melbourne, Australia: https://www. covidence. org/) was used to further screen and extract relevant studies. The full text of each selected article was reviewed to verify that it contained relevant information. To identify other potentially eligible publications, the bibliographic section of the selected articles was manually searched for additional relevant articles. Data on study-related outcomes in the individual studies were abstracted by two authors (DR and JS) and the two authors (DR and JS) did the quality scoring independently. The Jadad scale for RCT was used to assess the quality of studies.[10] The Newcastle–Ottawa scale was used for cohort studies.[10],[11]

Outcomes assessed in study cohorts were as follows

  1. Odds ratio (OR) of specimen adequacy
  2. Pooled rate of specimen adequacy
  3. OR of sample blood contamination
  4. Pooled rate of sample blood contamination
  5. OR of histologic accuracy
  6. Pooled rate of histologic accuracy.

Statistical analysis

We used meta-analysis techniques to calculate the pooled estimates in each case following the methods suggested by DerSimonian and Laird using the random-effects model.[12] We assessed heterogeneity between study-specific estimates using Cochran Q statistical test for heterogeneity and the I2 statistics.[13],[14],[15],[16] In this, values of <30%, 30%–60%, 61%–75%, and >75% were suggestive of low, moderate, substantial, and considerable heterogeneity, respectively.[17],[18],[19],[20]

Publication bias was ascertained qualitatively, by visual inspection of the funnel plot and quantitatively by the Egger test.[21],[22] P value <0.05 was considered statistically significant for comparison of groups. Statistical analyses were conducted using STATA software, version 16.0 (College Station, TX: StataCorp LLC).

  Results Top

Search results and study characteristics

From an initial total of 558 studies, 520 records were screened after deduplication, and 16 full-length articles were assessed. Six studies were ultimately include d in the final meta-analysis.[4],[7],[23],[24],[25],[26] The schematic diagram of study selection is illustrated in [Figure 1].
Figure 1: Study Prisma chart

Click here to view

A total of 418 patients (365 wet suction vs. 377 dry suction) were included in the final analysis. This analysis included a total of 535 lesions (332 pancreatic lesions and 203 nonpancreatic lesions). Patient age ranged from 26 to 87 years. Four studies used 22G needles for EUS-FNA, 1 study used 19G, 1 study used 25G, and 1 study used either 19G or 22G. Additional details of study characteristics with patient demographics are summarized in [Table 1].
Table 1: Study characteristics

Click here to view

Characteristics and quality of included studies

Full manuscript publications included three randomized control trials[4],[7],[25] and three prospective cohort studies.[23],[24],[26] One study was published as an abstract.[23] Four studies originated from the USA,[7],[23],[25],[26] one from China,[4] and one from Japan.[24] The detailed assessment of study quality is given in [Supplementary Table 3 [Additional file 3]].

Meta-analysis outcomes

  1. OR of sample adequacy: The pooled odds of sample adequacy was 3.18 (confidence interval [CI]: 1.82–5.54), favoring wet over dry suction EUS FNA, this was statistically different (P = 0.001) [Figure 2]
  2. Pooled rate of sample adequacy: The pooled rate of sample adequacy was 91.90% (CI: 89.10%–94.18%) in the wet-suction cohort and 77.32% (CI 73.37%-80.94%) in the dry-suction cohort (comparison P value <0.001)
  3. OR of blood contamination: The pooled odds of blood contamination was 1.18 (CI: 0.75–1.86) comparing the two study cohorts and this was not statistically different (P = 0.1)
  4. Pooled rate of blood contamination: The pooled rate for blood contamination was 58.33% (CI: 53.65%–62.90%) in the wet-suction cohort and 54.60% (CI: 49.90%– 59.24%) in the dry-suction cohort (comparison P value = 0.256)
  5. OR of histological diagnosis: The pooled odds of histological diagnosis was 3.68 (CI: 0.82–16.42) comparing the two study cohorts and this was not statistically different (P = 0.1)
  6. Pooled rate of histological diagnosis: The pooled rate for histological diagnosis was 84.06% (CI: 79.38%–88.05%) in the wet-suction cohort and 68.87% (CI: 63.31%–74.05%) in the dry-suction cohort (comparison P value <0.001).
Figure 2: Forest plots of specimen adequacy (a), blood contamination (b), and histological accuracy (c)

Click here to view

Validation of meta-analysis results

Heterogeneity and publication bias assessment

We assessed dispersion of the calculated rates using I2 percentage values. I2 tells us what proportion of the dispersion is true versus chance. We found no significant heterogeneity in reported sample adequacy analysis, moderate heterogeneity was observed in blood contamination analysis, and significant heterogeneity was observed in histological analysis. Publication bias analysis was visually assessed using funnel plots [Supplementary Table 4 [Additional file 4]].

  Discussion Top

We found that the wet-suction technique resulted in greater specimen adequacy when compared to the dry suction method. However, we found that blood contamination, and more importantly, histological accuracy, was comparable using either technique.

We found that the wet-suction cohort had a statistically significant improvement in the specimen adequacy when compared to the dry-suction cohort, with an OR of 3.18 (CI: 1.82–5.54, P = 0.001). Berzosa et al. had suggested that a column of water enhances tissue aspiration due to fluid dynamics and has been shown to allow greater volumes of tissue to be aspirated within the same simulation time when compared to a column of air.[5],[27]

Our study also demonstrated that there were comparable rates of blood contamination in the wet-suction cohort when compared to dry-suction cohort (pooled OR: 1.18, CI: 1.75–1.86, P = 0.1). A concern when using EUS-FNA is that the use of suction can often lead to higher rates of blood contamination and can negatively impact the overall quality of a specimen.[2] It was previously thought that the wet-suction technique would overcome this barrier.[4],[5] However, this meta-analysis did not reveal a statistically significant difference in blood contamination using either method.

We found that both the methods had comparable histological accuracy. Our analysis also failed to show a statistically significant difference in histological accuracy. This could be due to differences in needle gauge as a uniform needle gauge was not used throughout all studies. Furthermore, both the techniques had very low rates of complications which is consistent with previous studies.[20],[21]

The strengths of our review are as follows: systematic literature search with well-defined inclusion criteria, careful exclusion of redundant studies, inclusion of good-quality studies with detailed extraction of data, rigorous evaluation of study quality, and statistics to establish and/or refute the validity of the results of our meta-analysis.

There were also several limitations to this study, most of which are inherent to any meta-analysis. We were unable to calculate the histological accuracy, tissue adequacy, and blood contamination between the pancreatic, hepatic, and other lesions as these data were not consistently provided in all the studies. In addition, the needle gauge was not consistent throughout studies.

Our study is the most comprehensive review comparing the wet-suction and dry-suction techniques for the sampling of solid lesions performed to date. Ultimately, EUS-FNA performed using the wet-suction technique offered higher specimen quality but comparable rates of histological accuracy and blood contamination when compared to EUS-FNA dry suction.


The authors would like to thank Amy Bergeron for library support

Financial support and sponsorship


Conflicts of interest

Douglas G. Adler is an Editor of Endoscopic Ultrasound. The article was subject to the journal's standard procedures, with peer review handled independently of this Editor and his research groups. There are no other conflicts of interest.

Supplementary Materials

Supplementary information is linked to the online version of the paper on the Endoscopic Ultrasound website.

  References Top

Cazacu IM, Luzuriaga Chavez AA, Saftoiu A, et al. A quarter century of EUS-FNA: Progress, milestones, and future directions. Endosc Ultrasound 2018;7:141-60.  Back to cited text no. 1
Wallace MB, Kennedy T, Durkalski V, et al. Randomized controlled trial of EUS-guided fine needle aspiration techniques for the detection of malignant lymphadenopathy. Gastrointest Endosc 2001;54:441-7.  Back to cited text no. 2
Lee JK, Choi JH, Lee KH, et al. A prospective, comparative trial to optimize sampling techniques in EUS-guided FNA of solid pancreatic masses. Gastrointest Endosc 2013;77:745-51.  Back to cited text no. 3
Wang Y, Wang RH, Ding Z, et al. Wet- versus dry-suction techniques for endoscopic ultrasound-guided fine-needle aspiration of solid lesions: A multicenter randomized controlled trial. Endoscopy 2020;52:995-1003.  Back to cited text no. 4
Villa NA, Berzosa M, Wallace MB, et al. Endoscopic ultrasound-guided fine needle aspiration: The wet suction technique. Endosc Ultrasound 2016;5:17-20.  Back to cited text no. 5
Diehl DL, Mok SR, Khara HS, et al. Heparin priming of EUS-FNA needles does not adversely affect tissue cytology or immunohistochemical staining. Endosc Int Open 2018;6:E356-62.  Back to cited text no. 6
Attam R, Arain MA, Bloechl SJ, et al. “Wet suction technique (WEST)“: A novel way to enhance the quality of EUS-FNA aspirate. Results of a prospective, single-blind, randomized, controlled trial using a 22-gauge needle for EUS-FNA of solid lesions. Gastrointest Endosc 2015;81:1401-7.  Back to cited text no. 7
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Jadad AR, Moore RA, Carroll D, et al. Assessing the quality of reports of randomized clinical trials: Is blinding necessary? Control Clin Trials 1996;17:1-12.  Back to cited text no. 10
Peterson J, Welch V, Losos M, et al. The Newcastle-Ottawa scale (NOS) for Assessing the Quality of Nonrandomised Studies in Meta-Analyses. Ottawa: Ottawa Hospital Research Institute; 2011.  Back to cited text no. 11
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Sutton AJ, Abrams KR, Jones DR, et al. Methods for Meta-Analysis in Medical Research. New York: J. Wiley; 2000.   Back to cited text no. 13
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Mohan BP, Adler DG. Heterogeneity in systematic review and meta-analysis: How to read between the numbers. Gastrointest Endosc 2019;89:902-3.  Back to cited text no. 16
Higgins JP, Thompson SG, Deeks JJ, et al. Measuring inconsistency in meta-analyses. BMJ 2003;327:557-60.  Back to cited text no. 17
Kanwal F, White D. “Systematic Reviews and Meta-analyses” in clinical gastroenterology and hepatology. Clin Gastroenterol Hepatol 2012;10:1184-6.  Back to cited text no. 18
Guyatt GH, Oxman AD, Kunz R, et al. GRADE guidelines: 7. Rating the quality of evidence-inconsistency. J Clin Epidemiol 2011;64:1294-302.  Back to cited text no. 19
Easterbrook PJ, Berlin JA, Gopalan R, et al. Publication bias in clinical research. Lancet 1991;337:867-72.  Back to cited text no. 20
Duval S, Tweedie R. Trim and fill: A simple funnel-plot-based method of testing and adjusting for publication bias in meta-analysis. Biometrics 2000;56:455-63.  Back to cited text no. 21
Rothstein HR, Sutton AJ, Borenstein M. Publication Bias in Meta-Analysis: Prevention, Assessment and Adjustments. New York: John Wiley & Sons, 2006.  Back to cited text no. 22
Berzosa M, Villa N, Bartel MJ, et al. Mo1420 pilot study comparing hybrid vs. wet vs. dry suction techniques for EUS-FNA of solid lesions. Gastrointest Endosc 2014;79:AB430.  Back to cited text no. 23
Sugimoto M, Takagi T, Suzuki R, et al. Can the wet suction technique change the efficacy of endoscopic ultrasound-guided fine-needle aspiration for diagnosing autoimmune pancreatitis type 1? A prospective single-arm study. World J Clin Cases 2020;8:88-96.  Back to cited text no. 24
Mok SR, Diehl DL, Johal AS, et al. A prospective pilot comparison of wet and dry heparinized suction for EUS-guided liver biopsy (with videos). Gastrointest Endosc 2018;88:919-25.  Back to cited text no. 25
Hasan MK, Bang JY, Varadarajulu S. Diagnostic value of priming the endoscopic ultrasound-guided fine-needle aspiration needle with heparin to improve specimen quality. Dig Endosc 2014;26:491.  Back to cited text no. 26
Berzosa M, Uthamaraj S, Dragomir-Daescu D, et al. Mo1395 EUS-FN wet vs. dry suction techniques; a proof of concept study on how column of water enhances tissue aspiration. Gastrointest Endosc 2014;79:AB421-2.  Back to cited text no. 27


  [Figure 1], [Figure 2]

  [Table 1]


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    -  Ramai D
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    -  Khan SR
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