Many STIs can be diagnosed with blood tests, including HIV, genital herpes, and syphilis. Other STIs can be tested for using a swab taken from the mouth, anus, or sores.

At-home test kits allow you to swab yourself without visiting a doctor. However, these kits may contaminate your sample.

Chlamydia

Chlamydia is a sexually transmitted infection that is spread through unprotected oral, anal, and vaginal sex. Symptoms of chlamydia usually don’t show up right away, and many people don’t know they have it until they’re already spreading it to their sexual partners.

Women who follow CDC guidelines for yearly screening for chlamydia reduce their risk of infertility, pelvic inflammatory disease (PID), and other serious health problems. Routine testing also helps to build trust in relationships, and clinics can help you contact your sexual partners if needed to offer them treatment.

There are several different ways to test for chlamydia, including using swabs from the throat, mouth, genitals, or penis. STI tests that use urine samples are more common, as they’re less invasive and more convenient for doctors to administer.

Syphilis

Syphilis is a serious STD that can cause serious health problems if it’s not treated. It spreads through oral, vaginal and anal sex. Symptoms can include a painful sore in your mouth, on your genitals or on the anus or rectum. In the first stage, syphilis has no symptoms and is called primary syphilis. Then the infection hides (becomes latent) and may go into a second, third or fourth stage.

During the late stages of syphilis, a person may experience severe health complications like brain, nervous system and eye damage. The CDC recommends that all pregnant women get tested for syphilis during their first prenatal visit.

Most syphilis tests involve taking a sample of blood from a vein, dry blood spot or finger prick and sending it to a lab. Sometimes a swab of a sore or rash can be used.

Gonorrhea

Gonorrhea affects both male and female genitals, but most people only experience symptoms in their throat (from oral or anal sex) or on the penis. Symptoms include white, yellow or green discharge from the penis, pain when peeing and itching. Those with more severe symptoms can develop inflammation in the testicles or scrotum.

Untreated gonorrhea can spread to the uterus and fallopian tubes, leading to pelvic inflammatory disease (PID), infertility or ectopic pregnancy. It can also cause problems in newborn infants, including a life-threatening eye infection and joint and heart valve damage.

Treatment for gonorrhea includes antibiotics taken orally. People with gonorrhea should let their recent sex partners know they may have the infection to prevent transmission to them. This can be done anonymously using the Let Them Know website.

Trichomoniasis

Trichomoniasis is caused by a one-celled parasite called Trichomonas vaginalis. It’s passed during vaginal, oral or anal sex between people, and can also be spread to babies born to infected mothers.

Doctors can diagnose trichomoniasis by doing an exam of your genital area and lab tests. They might look at a sample of your vaginal fluid for women or a swab from inside the penis (urethra) for men under a microscope to spot the infection. They may also do a special test called a culture or a nucleic acid amplification test.

Your health care provider will prescribe antibiotic medicine to treat the infection. It’s important to take the full course of medication, and tell your partner(s) about the infection so they can get treated too.

Human Papillomavirus

The human papillomavirus (HPV) is the most common sexually transmitted infection in the United States. It causes genital warts and some types of cancer. HPV vaccines can prevent the infection.

Most people have genital HPV at some time in their lives without having any symptoms. HPV can also cause cancer of the vulva and the cervix. HPV can affect men and women equally.

Regular screening with a Pap test or colposcopy can find cell changes in the cervix before they become cancer. Pap tests can detect most types of cervical cancer. The US Preventive Services Task Force recommends all women get a Pap test starting at age 21, regardless of their sexual activity. Vaccines can help prevent genital HPV infections and cancers. HPV DNA tests can be used to identify the strains of genital HPV that increase a person’s risk for genital warts and cervical cancer.