This study investigated the effects of varicocele on semen parameters in infertile men based on the new 2010 World Health
Organization laboratory manual for the examination of human semen. Semen analysis results (volume, sperm count, motility, and
morphology) were the primary outcomes. An electronic search to collect the data was conducted using the Medline/PubMed, SJU
discover, and Google Scholar databases. We searched articles published from 2010 to August 2015, i.e., after the publication of
the 2010 WHO manual. We included only those studies that reported the actual semen parameters of adult infertile men diagnosed
with clinical varicocele and contained a control group of either fertile men or normozoospermic men who were not diagnosed with
varicocele. Ten studies were included in the meta‑analysis, involving 1232 men. Varicocele was associated with reduced sperm
count (mean difference: −44.48 × 106 ml−1; 95% CI: −61.45–−27.51 × 106 ml−1; P < 0.001), motility (mean difference: −26.67%;
95% CI: −34.27–−19.08; P < 0.001), and morphology (mean difference: −19.68%; 95% CI: −29.28–−10.07; P < 0.001) but
not semen volume (mean difference: −0.23 ml; 95% CI: −0.64–0.17). Subgroup analyses indicated that the magnitude of effect
was influenced by control subtype but not WHO laboratory manual edition used for semen assessment. We conclude that varicocele
is a significant risk factor that negatively affects semen quality, but the observed pooled effect size on semen parameters does not
seem to be affected by the WHO laboratory manual edition. Given most of the studies published after 2010 still utilized the 1999
manual for semen analysis, further research is required to fully understand the clinical implication of the 2010 WHO laboratory
manual on the association between varicocele and semen parameters.

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