Reducing inter-laboratory differences, semen analyses using Z score and regression transformations

Esther Leushuis*, Alex Wetzels, Jan Willem Vandersteeg, Pieternel Steures, Patrick M.M. Bossuyt, Netty Vantrooyen, Sjoerd Repping, Frans A.L. Vanderhorst, Peter G.A. Hompes, Ben Willem J. Mol, Fulco Vanderveen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


Background: Standardization of the semen analysis may improve reproducibility. We assessed variability between laboratories in semen analyses and evaluated whether a transformation using Z scores and regression statistics was able to reduce this variability. Materials and Methods: We performed a retrospective cohort study. We calculated between-laboratory coefficients of variation (CVB) for sperm concentration and for morphology. Subsequently, we standardized the semen analysis results by calculating laboratory specific Z scores, and by using regression. We used analysis of variance for four semen parameters to assess systematic differences between laboratories before and after the transformations, both in the circulation samples and in the samples obtained in the prospective cohort study in the Netherlands between January 2002 and February 2004. Results: The mean CVBwas 7% for sperm concentration (range 3 to 13%) and 32% for sperm morphology (range 18 to 51%). The differences between the laboratories were statistically significant for all semen parameters (all P<0.001). Standardization using Z scores did not reduce the differences in semen analysis results between the laboratories (all P<0.001). Conclusion: There exists large between-laboratory variability for sperm morphology and small, but statistically significant, between-laboratory variation for sperm concentration. Standardization using Z scores does not eliminate between-laboratory variability.

Original languageEnglish
Pages (from-to)534-540
Number of pages7
JournalInternational Journal of Fertility and Sterility
Issue number4
Publication statusPublished - 1 Jan 2016


  • Differences
  • Regression
  • Semen analysis
  • Standardization


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