What is the appropriate ICD-10 (International Classification of Diseases, 10th Revision) code and treatment approach for a male-to-female transgender patient being referred to endocrinology for hormone replacement therapy (HRT)?

ICD-10 Coding and Endocrinology Referral for Male-to-Female Transgender Patients

For a male-to-female transgender patient requiring endocrinology referral for hormone therapy, use ICD-10 code F64.0 (Transsexualism) or the broader F64.9 (Gender identity disorder, unspecified), with F64.0 being more specific and preferred when the patient clearly identifies as a transgender woman seeking medical transition. 1

ICD-10 Code Selection

The current ICD-10 system in the United States uses codes from the F64 series for gender-related diagnoses:

• F64.0 (Transsexualism): Most specific code for transgender women (assigned male at birth, female gender identity) seeking medical transition 1, 2
• F64.8 (Other gender identity disorders): Used for gender-nonconforming or nonbinary individuals 1
• F64.9 (Gender identity disorder, unspecified): Broader code when specific identity is unclear 1, 2

Important context: These codes remain necessary for insurance billing and reimbursement despite the terminology being outdated. 1 The ICD-11 has replaced "gender dysphoria" with "gender incongruence" and moved it to a sexual health chapter, but ICD-10 remains in use in the United States. 1

Coding Sensitivity and Specificity

Chart review studies demonstrate that F64 codes have 88-100% sensitivity in identifying transgender patients, with the majority being transgender women when combined with clinical context. 2 However, false negatives occur at approximately 15%, meaning some transgender patients may not have these codes documented. 2

Documentation Best Practices

When making the endocrinology referral, include the following specific information:

• Sex assigned at birth: "Assigned male at birth" (avoid outdated terms like "biologically male" or "natal male") 1
• Current gender identity: "Transgender woman" or "trans woman" 1
• Preferred name and pronouns: Document affirmed name (not "dead name") and pronouns (typically she/her) 1
• Organ inventory: Specify presence of testes, prostate, and any prior gender-affirming surgeries 1
• Duration of social transition: If applicable 1

Referral Content for Endocrinology

Your referral should specify the patient is seeking gender-affirming hormone therapy (GAHT) for male-to-female transition. 1, 3

Pre-Referral Baseline Assessment

Before or concurrent with endocrinology referral, ensure the following baseline labs are obtained:

• Complete blood count (hemoglobin will decrease with estrogen therapy) 1, 4
• Comprehensive metabolic panel (liver function, kidney function) 4
• Lipid profile 4
• Fasting glucose 4
• Baseline hormone levels (testosterone, estradiol) 3, 4

Expected Hormone Therapy Regimen

Inform the patient that endocrinology will likely prescribe:

Estradiol (cornerstone of feminizing therapy):

• Available as oral, transdermal patch, or injectable forms 1, 3
• Target estradiol levels: Adult cisgender female reference range 3
• Induces breast development, decreased muscle mass (3-5% reduction in lean body mass), skin softening, decreased body/facial hair, and feminized body composition 1, 3

Anti-androgen therapy (to suppress testosterone):

• Spironolactone: Most commonly used in the United States, starting dose typically 50-200 mg daily (not 25 mg as sometimes suggested) 3
• Alternative options: Cyproterone acetate, GnRH agonists, bicalutamide, or finasteride 1, 3
• Target testosterone level: <50 ng/dL (female range) 3

Timeline of Physical Changes

Set realistic expectations:

• Breast development occurs over 3+ years, with variable results (cup sizes ranging from A to E, though most fall in A-B range) 1, 3
• Muscle mass decreases by 5% in thigh volume and 4% in quadriceps cross-sectional area, though transgender women retain greater muscle mass than cisgender women 1
• Hemoglobin decreases significantly to female reference range 1

Critical Safety Considerations

Cardiovascular Risk

Transgender women on estrogen therapy have significantly elevated thrombotic risk compared to both cisgender men and cisgender women, including those on oral contraceptives or menopausal hormone therapy. 3

Specific risks include:

• Venous thromboembolism (VTE): Three-fold increased risk compared to cisgender women 3
• Ischemic stroke: Elevated risk independent of estrogen formulation 3
• Myocardial infarction: Increased risk 3
• Cardiovascular death: Three-fold increase compared to cisgender women 3

Clinical pitfall: The VTE risk in transgender women is dose-dependent and persists despite modern estradiol preparations. 3 Avoid ethinyl estradiol, which carries even higher VTE risk. 3

Monitoring Protocol

Endocrinology will implement the following schedule:

• 3 months: Check estradiol and testosterone levels, adjust doses 3, 4
• Every 3-6 months during first year: Hormone levels, clinical response 3, 4
• Annually once stable: Hormone levels, cardiovascular risk assessment, lipids, glucose 4

Common Pitfalls to Avoid

1. Using outdated or offensive terminology: Never use "transvestite," "transgenderism," or "transsexual" (unless patient specifically prefers it). Use "transgender woman" or "trans woman" as an adjective, not "a transgender." 1

2. Calling patient by birth name: Always use affirmed name throughout all documentation and verbal communication. 1

3. Assuming mental health diagnosis: Gender identity is not a mental health condition per se; the F64 codes are used for billing purposes only. 1

4. Inadequate cardiovascular risk assessment: Given the elevated VTE and cardiovascular risks, screen for additional risk factors (smoking, obesity, thrombophilia, age >40, hypertension). 3

5. Misinterpreting lab values: After >1 year of hormone therapy, interpret most lab values (except hormone levels themselves) based on affirmed gender (female reference ranges). 5, 4

Fertility Counseling

Before initiating hormone therapy, endocrinology should provide fertility preservation counseling, as feminizing hormone therapy may permanently affect fertility. 4 If the patient desires future biological children, sperm banking should be discussed before starting GAHT.

Mental Health Support

While not required for hormone therapy initiation per current guidelines, be aware that transgender individuals have higher rates of anxiety, depression, and suicidality. 1, 4 Gender-affirming hormone therapy itself improves quality of life and reduces depression and suicidality. 1