Washington has explicit insurance guidance on transgender-related health care.

Statutes:

• SB 5313 (2021)
  Summary:

  Sec. 2 “(4) Gender affirming treatment must be covered in a manner compliant with the federal mental health parity and addiction equity act of 2008 and the federal affordable care act. Gender affirming treatment can be prescribed to two spirit, transgender, nonbinary, intersex, and other 36 gender diverse individuals. (5) Nothing in this section may be construed to mandate coverage of a service that is not medically necessary."

  Sec. 4 “(2)(a) The authority and any managed care plans delivering or administering services purchased or contracted for by the authority may not apply categorical cosmetic or blanket exclusions to gender affirming treatment. (b) Facial feminization surgeries and facial gender affirming treatment, such as tracheal shaves, hair electrolysis, and other care 30 such as mastectomies, breast reductions, breast implants, or any 31 combination of gender affirming procedures, including revisions to prior treatment, when prescribed as gender affirming treatment, may not be excluded as cosmetic.”

Regulations:

• Wash. Admin. Code 284-43-5940
  Summary:

  (A) “Any health services that are ordinarily or exclusively available to individuals of one sex, based on the fact that an individual's sex assigned at birth, gender identity, or gender otherwise recorded is different from the one to which such health services are ordinarily or exclusively available. For example, a denial of coverage for medically necessary hormone prescriptions for transgender, gender nonconforming, or intersex individuals because the dosages exceed those typically prescribed for cisgender people would be discriminatory against transgender, nonbinary, gender nonconforming, or intersex individuals...”

  (vi) "When prescribed as medically necessary, exclude facial gender affirming treatment (such as tracheal shaves), hair removal procedures, and other care (such as mastectomies, breast reductions, breast implants, or any combination of gender affirming procedures, including revisions to prior treatment) as cosmetic services..."

Bulletins and Announcements:

• Guidance: Letter re: Transgender Health Nondiscrimination Protections
  Issued by: Insurance Commissioner Mike Kreidler
  Issued on: June 23, 2020
  Summary:

  This letter was sent to insurers in response to the announcement the Trump administration made that it intends to limit the protections transgender patients have under the Affordable Care Act. It was accompanied by a press release.

• Guidance: Letter to Health Insurance Carriers in Washington State
  Issued by: Washington Office of Insurance Commissioner
  Issued on: June 25, 2014
  Summary:

  “Reading the provisions of state law in conjunction with the definitions contained in Washington state’s Law Against Discrimination, and the requirements of the federal Affordable Care Act, it is clear that exclusions, prohibitions, and other forms of discrimination by issuers against policy holders who identify as transgender is prohibited.”