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No measurable marker for gender identity

There is no validated biological test that can establish or refute 'gender identity': no blood value, no hormone profile, no scan, no gene. According to the Cass Review, research has so far not reliably identified brain changes directly linked to gender incongruence (para. 8.20) (source).

What a marker should be

A biological marker is a measurable indicator of a biological state. For diabetes: HbA1c. For pregnancy: hCG. For sex : gametes, karyotype, gonadal anatomy. For "gender identity": nothing. No lab test, no scan, no criterion. It is impossible for a doctor to determine that someone has a "female gender identity" — he can only repeat what the patient says. That is not diagnosis; that is dictation.

What research has tried — and did not find

Brain scans ( no brain marker ), genetic studies ( no genetic marker ), hormone levels, finger-length ratios, the classic 'trans brain' claims around the Zhou BSTc study : nothing has produced a consistent, replicable, clinically useful distinction. According to the Cass Review (2024), research has so far not reliably identified brain changes directly linked to gender incongruence (para. 8.20), and there is no clear evidence of a simple biological cause (para. 8.21). Moreover, a formal diagnosis of gender dysphoria does not reliably predict whether a young person will remain gender incongruent, or whether medical treatment is the best option (source).

The epistemic consequence

Without a marker, only self-reporting remains. But self-reporting without an independent criterion immediately falls into circular reasoning : "I am trans because I feel trans, and I feel trans because I am trans." This is not a detail. It is a fundamental epistemic defect. In operational terms, we do not even know what we are talking about. The claim is unfalsifiable and is therefore, strictly speaking, a metaphysical claim , not a scientific one.

Comparison with actual diagnoses

For depression or ADHD there are no direct biomarkers, but there are validated behavioural scales, observation criteria and outcome measures. For gender dysphoria, according to the Cass Review, few guidelines recommend formal measurement tools, and the existing ones are poorly validated (para. 10.8) (source). That difference makes the concept fundamentally unsuitable as a basis for irreversible medical interventions. In her foreword, Hilary Cass writes that there are few other areas of healthcare where professionals are so afraid to openly discuss their views (source).