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Background: Blood (serum) testing is the standard method for monitoring testosterone (T) replacement therapy (TRT). Nevertheless, alternative methods, such as saliva testing, are gaining popularity because of their practical advantages. Objective: This review aims to offer evidence-based, clinically relevant information to enable healthcare providers to make rational decisions regarding management of TRT. Providers need to know which combinations of ROA (route of administration) and testing method best track and reflect dosing and clinical outcomes. To that end, we summarize the large body of evidence for serum T testing during transdermal (TD) TRT monitoring, as well as the smaller body of evidence for saliva T testing in the context of TRT. Also discussed is T testing via capillary dried bloodspot (DBS) and urine. We chose to focus on TD formulations (gels, creams) because they are well-studied and commonly prescribed. Methods: We conducted a literature search using online databases (PubMed/MEDLINE, ScienceDirect, and Google Scholar) and also reviewed real-world evidence available from large commercial laboratory databases. The clinical interpretation of these findings are discussed with regard to which tests best reflect clinical reality. Results: deletion. Conclusions: saliva and DBS T testing lack sufficient clinical correlation and should not be used for TD TRT monitoring. In particular, saliva T testing with TD TRT can yield misleading, erroneously high results, which can open the door to underdosing, loss of therapeutic benefit, and safety concerns.
Newman et al. (2026) studied this question.