Evidence check: Testosteron in the context of fertility

Testosterone is crucial for male fertility, especially for spermatogenesis. Deficiency can impair sperm production and quality, but the relationship is nuanced: both low and high levels can disrupt fertility. Direct-to-consumer (DTC) tests (saliva or blood) typically measure total testosterone, not free or bioavailable fractions, and ignore diurnal variation or other key hormones (LH, FSH, prolactin). Evidence for using such tests to assess fertility is weak; they cannot replace clinical evaluation. For couples trying to conceive, a doctor should perform comprehensive hormone panels and semen analysis. Genetic variants (e.g., in AR, INSL3) are rarely included in DTC panels or lack clinical validation. Conclusion: Testosterone matters, but a single measurement without context is misleading. Evidence: human-moderate for the general role; for DTC fertility tests: limited.