HK’s public sector Social Hygiene Clinics offer free STD tests for eligible HKID holders, just walk-in and get tested on same day. It has to be a Social Hygiene clinic; and, not a Dermatological Clinic.
Please select your preferred location (call to book) …
https://www.dh.gov.hk/english/tele/tele_chc/tele_chc_dc.html
https://www.dh.gov.hk/english/useful/useful_fee/useful_fee.html
Fees and Charges for Public Health Care Services provided by the Department of Health
1. Patients falling into the following categories are eligible for the rates of charges applicable to Eligible Persons:
(i) holders of Hong Kong Identity Card issued under the Registration of Persons Ordinance (Chapter 177), except those who obtained their Hong Kong Identity Card by virtue of a previous permission to land or remain in Hong Kong granted to them and such permission has expired or ceased to be valid;
https://www.dh.gov.hk/english/useful/useful_fee/useful_fee_os.html
OUTPATIENT SERVICES.
(A) Eligible Persons:
f) Attendance at Social Hygiene and Special Skin Clinics for any investigation or treatment relating to sexually transmitted diseases or leprosy, Maternal and Child Health Centres and Tuberculosis and Chest Clinics:
No charge.
(B) Non-eligible Persons: Item f) HKD $1,190.