BACKGROUNDHerein, we describe the consensus guideline methodology, summarize the evidence-based recommendations we provided to the World Health Organization (WHO) for their consideration in the development of global guidance and present a narrative review of the diagnosis of male infertility as related to the eight prioritized (problem or population (P), intervention (I), comparison (C) and outcome(s) (O) (PICO)) questions. Additionally, we discuss the challenges and research gaps identified during the synthesis of this evidence.OBJECTIVE AND RATIONALEThe aim of this paper is to present an evidence-based approach for the diagnosis of male infertility as related to the eight prioritized PICO questions.SEARCH METHODSCollating the evidence to support providing recommendations involved a collaborative process as developed by WHO, namely: identification of priority questions and critical outcomes; retrieval of up-to-date evidence and existing guidelines; assessment and synthesis of the evidence; and the formulation of draft recommendations to be used for reaching consensus with a wide range of global stakeholders. For each draft recommendation the quality of the supporting evidence was then graded and assessed for consideration during a WHO consensus.OUTCOMESEvidence was synthesized and recommendations were drafted to address the diagnosis of male infertility specifically encompassing the following: What is the prevalence of male infertility and what proportion of infertility is attributable to the male? Is it necessary for all infertile men to undergo a thorough evaluation? What is the clinical (ART/non ART) value of traditional semen parameters? What key male lifestyle factors impact on fertility (focusing on obesity, heat and tobacco smoking)? Do supplementary oral antioxidants or herbal therapies significantly influence fertility outcomes for infertile men? What are the evidence-based criteria for genetic screening of infertile men? How does a history of neoplasia and related treatments in the male impact on (his and his partner's) reproductive health and fertility options? And lastly, what is the impact of varicocele on male fertility and does correction of varicocele improve semen parameters and/or fertility?WIDER IMPLICATIONSThis evidence synthesis analysis has been conducted in a manner to be considered for global applicability for the diagnosis of male infertility.

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The acrosome reaction of spermatozoa appears to be analogous to various somatic cell exocytotic events which involve cascade reactions, i.e., transmission of an external signal across the cell membrane resulting in activation of an "amplifier" enzyme and the generation of a second messenger. Using a synchronous acrosome reaction system (De Jonge et al., J. Androl., 10:232-239, '89a), it was found that analogues of the second-messenger cAMP, dibutyryl cAMP (dbcAMP) and 8-bromo cAMP, stimulated the acrosome reaction of capacitated spermatozoa. Additionally, treatment of spermatozoa with either xanthine or non-xanthine phosphodiesterase inhibitors induced a significant (P less than 0.05) increase in the percent acrosome reaction after a period of capacitation in comparison to untreated controls. These results indicate that analogues of cAMP or inhibitors which prevent cAMP hydrolysis can induce the human sperm acrosome reaction. Subsequent experiments were conducted to test whether the amplifier enzyme in the cascade reaction, adenylate cyclase, has a role in the acrosome reaction. Forskolin, an adenylate cyclase stimulator, caused a significant (P less than 0.01) increase in the percent acrosome reaction in comparison to controls. Modulators of adenylate cyclase--adenosine, 2'-0-methyladenosine, and 2',3'-dideoxyadenosine--significantly (P less than 0.01) inhibited the forskolin-induced acrosome reaction. dbcAMP was able to overcome the inhibition by adenosine. Two inhibitors of protein kinase A, the Walsh inhibitor and H-8, caused a significant (P less than 0.01) inhibition of the dbcAMP-induced acrosome reaction. Finally, in the absence of extracellular calcium, dbcAMP induced a significant (P less than 0.01) increase in the acrosome reaction in contrast to A23187. These results suggest that: 1) a molecular mechanism for the human sperm acrosome reaction involves the cAMP second-messenger system; i.e., activation of adenylate cyclase, the amplifier enzyme that produces cAMP, production of cAMP as a second messenger, and activation of cAMP-dependent kinase A; and that 2) activation of adenylate cyclase occurs after calcium influx.