Referrals for gender-affirming healthcare services have surged in recent decades, presumably driven by increased visibility, acceptance and reduced barriers to care. Despite these advances, transgender and gender-diverse individuals continue to face significant mental health challenges, including elevated rates of anxiety, depression as well as high prevalence of autistic traits. Gender-affirming hormonal treatment (GAHT) has been suggested to improve mental health and quality of life (QoL) among transgender individuals; however, the short- and long-term treatment effects of GAHT are not yet fully understood. Therefore, this study aims to establish a comprehensive cohort of transgender individuals at the Centre for Gender Identity (CGI), Aalborg University Hospital, Denmark, to enhance understanding and treatment outcomes.

The Transgender Cohort (TraCK) will recruit participants from February 14, 2024, with recruitment occurring continuously alongside yearly follow-up. This single-centre cohort study will include both retrospective and prospective data collection. Transgender individuals referred to CGI will be invited to participate in the study via the Danish digital mail system called e-Boks. Participants must provide informed consent and complete a baseline questionnaire. Data will be collected from self-reported questionnaires and medical records across multiple specialists. Self-reported questionnaires include WHO-Quality of Life BREF, Eating Disorders Examination Questionnaire, Autism Spectrum Quotient, Transgender Congruence Scale, and Gender Minority Stress and Resilience Measure. Medical records will provide information on demographics, mental health, physical health, and gender-affirming treatment details. Data will be managed using REDCap, ensuring compliance with GDPR and the National Data Protection Act.

While recognising the potential privacy risks associated with data collection, the study considers these outweighed by the benefits of advancing knowledge on gender diversity and the impacts of gender-affirming care. The North Jutland Region Ethics Committee reviewed the project, determining no formal approval was needed, but it was registered and approved (no. F2024-012) by the North Jutland Region. Findings will be disseminated through peer-reviewed journals, conferences, and accessible reports for participants.

This study is registered with the North Jutland Region (no. F2024-012). Recruitment and data collection began on February 14, 2024, and will continue alongside yearly follow-up. Transgender individuals, transgender and gender-diverse, transgender cohort, transgender health, transgender research, cohort study, gender-affirming care.

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Transgender and gender-diverse (TGD) individuals have a gender identity that does not match the sex assigned to them at birth.1 To address gender incongruence, gender-affirming healthcare services can be provided. Over the past decades, there has been a significant increase in referrals for these services.2 3 This rise in referrals may be attributed to the notable increase in visibility, acceptance and destigmatisation of transgender people, likely driven by greater awareness through the internet and social media.4 Another contributing factor could be lowered barriers to healthcare, enabling more individuals to obtain gender-affirming treatment.4

However, transgender individuals still face a variety of challenges in their daily lives, including mental health problems such as anxiety, depression, and eating disorders as well as a high prevalence of autistic traits.5–10 Studies have shown that the mental health and quality of life (QoL) among transgender individuals can be improved by gender-affirming hormonal treatment (GAHT).11–14 GAHT consists of either feminising or masculinising hormone therapy, depending on the assigned sex at birth. In Europe, feminising GAHT commonly includes oestrogen in combination with testosterone-blocking treatment consisting of either cyproterone acetate, spironolactone or gonadotropin-releasing hormone agonist. Masculinising GAHT consists only of testosterone.13 15–18

There are two overall goals of GAHT, including (1) a reduction of endogenous sex hormones to achieve a decrease in secondary sex characteristics and (2) a replacement of endogenous sex hormones to develop secondary sex characteristics that align with the individual’s gender identity.19 The critical effects of feminising GAHT occur through stimulation of secondary sex characteristics, including breast growth, fat redistribution at the hips, decreased body hair, skin softening, and reduced erections.17 19 Masculinising GAHT induces virilisation, which leads to an increase in facial and body hair growth, a deeper voice, an increase in muscle mass, and amenorrhea.19 20

Besides the gender-affirming effects of GAHT, side effects may occur. Common side effects of feminising GAHT include decreased libido, mood swings, weight gain, increased risk of venous thromboembolism, and cardiovascular disease.21 22 Common side effects of masculinising GAHT include increased risk of acne, alopecia, erythrocytosis, sleep apnoea, and hypertension.19 21

Gender-affirming healthcare is offered in most European countries and is often provided by multidisciplinary centres.2 23–25 In Denmark, comprehensive support for transgender individuals is offered by the Danish free public healthcare service, and medication is partially reimbursed.2 These healthcare services include GAHT and gender-affirming surgeries and are provided by a mandatory multidisciplinary team including psychologists, psychiatrists, gynaecologists, endocrinologists, and plastic surgeons in one of the three public Centres for Gender Identity.2 26

Despite the crucial role of specialised healthcare centres in providing personalised, comprehensive and professional care for transgender individuals, recent studies from Denmark have shown that hormone use outside of these services is common among this patient group with a rate of approximately 20%.27 28 This rate reflects an unmet need in the Danish healthcare service and is influenced by the easy access to medication purchased via the internet.27 28 Notably, it has been reported that individuals who use hormones outside of healthcare services are often less aware of potential side effects, leaving them at a higher health risk compared with those who seek care from qualified physicians.19 21 22 29

All of this illustrates the importance of addressing the challenges of transgender individuals and providing the appropriate treatment. Moreover, there is a need to strengthen the evidence base concerning short- and long-term treatment effects through large, prospective cohort studies to guide the care of individuals experiencing gender incongruence.2 26 With an extended knowledge of the challenges faced by transgender individuals, increasing awareness of effective treatments, and greater knowledge regarding the impact of these treatments on QoL, mental well-being and physical health, healthcare professionals can provide stronger evidence-based recommendations. Hence, it is crucial to obtain a systematic overview of transgender individuals and to monitor treatment effects and consequences.

The Transgender Cohort called TraCK (Transkohorte ved Center for Kønsidentitet) is based at the CGI and is developed in a multidisciplinary collaboration with the Department of Obstetrics and Gynaecology, Department of Endocrinology and the Psychiatric Research Unit at Aalborg University Hospital, as well as the Department of Health Science and Technology at Aalborg University. The study plans to recruit participants from 14 Feruary 2024, and recruitment will occur continuously alongside yearly follow-up.

Data will be collected, stored and managed using Research Electronic Data Capture (REDCap),37 38 an electronic data capture tool hosted at Aalborg University Hospital, Denmark.37 38 REDCap is a secure, web-based software platform designed to support data capture for research studies, providing (1) an intuitive interface for validated data capture; (2) audit trails for tracking data manipulation and export procedures; (3) automated export procedures for seamless data downloads to common statistical packages; and (4) procedures for data integration and interoperability with external sources. Personal information will be managed in compliance with GDPR and the National Data Protection Act and was registered in North Denmark Region’s internal directory, ID number F2024-012.37 38

Potential risks associated with this study centre around data collection and privacy concerns. We acknowledge that the questionnaire contains personal and sensitive information, potentially leading to negative, uncomfortable or distressing emotions among some participants. Hence, it is crucial to always uphold the dignity and autonomy of the participants. However, we consider that the benefits outweigh the minimal risks, as this cohort will generate new knowledge and understanding related to psychological and physiological aspects of gender identity and both short- and long-term treatment effects. This comprehension is essential for enhancing the evidence base regarding gender-affirming care. The project was submitted to the Ethics Committee for the North Jutland Region (no. 108239), which assessed on November 14, 2023, that this project does not require approval. However, TraCK has been registered and approved on February 1, 2024, by the North Jutland Region (no. F2024-012). The findings from this cohort will be disseminated through international peer-reviewed journals and national and international congresses. Besides this, participants involved in this study can gain insight into the latest research by contacting the database administrator.