Evaluating testis function non-invasively: how epidemiologist–andrologist teams might better approach this task

Opinions herein focus on epidemiology-based publications using semen to study testis function, but several have broader applicability. 'Opinion 1': authors often fail to write out an explicit question(s) or hypothesis, and to stipulate how measured outcomes will be used to refute or support the hypothesis. Might critical thinking be lax? 'Opinion 2': authors often fail to consider the biology underlying a question or hypothesis, and/or which analytical methods really provide meaningful information or should be rejected. 'Opinion 3': spermatogenesis cannot be evaluated in a meaningful manner via conventional semen attributes. Quantitative evaluation of spermatogenesis requires a 'rate attribute', not provided by number of sperm per milliliter of semen or total number per ejaculate (TSperm). Influence of abstinence interval is under-appreciated. The rate attribute, TSperm per hour of abstinence (TSperm/h), meaningfully estimates sperm production if the abstinence interval is 42-60 h. Most attributes of individual sperm do not reflect quality at spermiation. 'Opinion 4': reliance on a single semen sample per subject might hamper detection of the association sought, because an imprecise value might not establish if a subject's testes were dysfunctional or not. 'Opinion 5': curve-fitting, to adjust quantitative data, for a sample provided after an abstinence interval falling within a broad range, to a standardized abstinence interval, distorts outcomes for many samples provided after approximately 60 h abstinence. TSperm values for individuals with good daily sperm production are artifactually low and those for individuals with poor daily sperm production are artifactually high. Hence, it is important to explain the importance of abstinence interval to participants and censor samples outside an acceptable 37-64 h abstinence range.