Section 1
Why can an infection be symptom-free?
Chlamydia and gonorrhoea are well-known examples of infections that may cause no obvious symptoms. Herpes can also be transmitted when no sore is visible. This is why visual inspection of a partner cannot confirm sexual-health status.
Source: World Health Organization — Sexually transmitted infectionsCDC — Getting tested for STDs
Section 2
Which possible STD symptoms deserve assessment?
Possible signs include unusual discharge, burning urination, sores, blisters, rash, pelvic discomfort, testicular pain, bleeding after sex or other unexplained genital changes.
These symptoms are not proof of an STD. Urinary, skin, hormonal and other conditions can cause similar changes. Avoid self-treatment with leftover antibiotics because it may delay the correct diagnosis and contribute to resistance.
Source: World Health Organization — Sexually transmitted infections
Section 3
Should you test when you feel completely well?
Screening can still be appropriate after a new partner, unprotected contact, a partner's positive result or as part of a risk-based routine plan.
There is no universal panel or schedule for everyone. Ask which infections are included, whether throat or rectal samples are relevant, and whether an early test needs repeating.