Will A Blood Test Detect All STDs?

I am going to the gynecologist next week and I am going to get an STD test. I have always been safe, but I still like to get checked. I am going to get a blood test. Will that detect everything? Or is there anything else that I can do?

First, it is important to realize that neither blood tests nor physical exams will identify all STDs, although doing both an exam and blood tests can pinpoint most. Ignoring the rarer STDs, at least in this country — like chancroid or lymphogranuloma venereum — I will go one by one through the common STDs to discuss how they are diagnosed, and what tests may help in their identification.

Chlamydia and gonorrhea: These two STDs are similar in that both are caused by bacteria, both live in the urethra in men and the cervix in women, and both can cause serious complications, epididymitis (an infection of the tubes behind the testes which channel sperm up to the seminal vesicles) in men and pelvic inflammatory disease and/or infertility in women. Chlamydia may cause no symptoms in either men or women, and even gonorrhea often causes no symptoms in women. Although blood tests have been developed for research purposes for both diseases, there are no practical blood tests available to regular doctors. Both can be diagnosed by running a swab into the urethra in men and the cervix in women, which is then sent to the lab. The test takes several days to return. Asymptomatic men who want this test should ask specifically for it, since it’s now always part of routine STD testing. Similarly, women who are having a Pap smear should also ask for the swab test, and not just assume that it will be done. There is also a urine test for both chlamydia and gonorrhea which is slowly replacing the blood and swab tests.

Syphilis: Also a bacterial disease, syphilis typically first causes a painless ulcer, usually on the genitals but occasionally around the mouth or elsewhere. A good screening blood test exists, and will almost certainly be ordered by almost all doctors if one asks to be tested for STDs. In someone with a syphilitic ulcer, called a chancre, the test will usually not be positive, and the diagnosis must be made by examination and special testing of the ulcer. Such testing is not available in most doctors’ offices, and usually requires referral to a department of health STD clinic, or perhaps a hospital.

Herpes: Herpes is the other common STD that causes ulcers, usually multiple small ones which itch and then sting, and heal in seven to ten days. Most people (80 percent) have herpes in or around their mouths from childhood, where it may show up from time to time as cold sores on the lips. Blood tests for both the oral form, herpes I, and the genital form herpes II do exist, but they are expensive, and would seldom be ordered by a doctor if simply asked to check someone out for STDs. (There are, however, simpler and less expensive new blood tests that can tell you if you have type I or type II herpes. People who want this test should ask for it as it may help them from being unknowing asymptomatic transmitters.) If an ulcer is present, a culture can be done. No physical examination will detect herpes unless a sore is present; thus, to be really sure about this STD, the blood test would be necessary. Since herpes is an annoying but not serious illness in most people, I don’t think doing the blood tests routinely is justifiable. Large-scale testing has shown that about 30 percent of people who have a positive blood test for herpes II have never had an outbreak.

Human papilloma virus (HPV): Although blood tests for HPV have been done for research purposes, no such tests are available to most doctors. Therefore, the diagnosis is made on the basis of physical exam, that is checking for warts on the genitals, or by observing typical wart changes on a Pap smear. In addition, there is a new HPV test called the Hybrid Capture II, which is currently approved for women who have had an abnormal Pap. To thoroughly check a male penis for warts requires soaking it in vinegar for several minutes to make any wart more obvious, and then inspecting the penis with at least a magnifying glass. Few doctors do this when asked to check for STDs. Putting vinegar on a woman’s genitals and then inspecting them closely with a magnifying glass is seldom done during a routine Pap, but is often done when a woman has a colposcopy. The strains of HPV causing most cases of cervical cancer in women, HPV 16 and 18 and others do not seem to produce visible warts in most men even when the vinegar soaking is done. Where the virus resides in men, who obviously transmit it to women, is something of a mystery.

HIV and hepatitis B: These are the really nasty STDs, and there is nothing on physical examination that will allow a doctor to diagnose either of them. Both are caused by viruses, and good blood tests are available for both (there is also a vaccination available for hepatitis B). Any doctor asked to check for STDs should, I believe, do them; but testing for HIV is made complicated in many states by special regulations, and many doctors will simply tell someone asking for HIV testing to go to the local department of health. Having to make that extra trip will, of course, discourage many people.

To summarize, the only blood tests commonly done for STDs test for syphilis, HIV and hepatitis B. A blood test for herpes exists but is seldom done. A good urethral test for gonorrhea and chlamydia exists, but is seldom done in men unless specifically requested. HPV is diagnosed by inspection, and I believe men and women commonly carry the virus without showing any signs on an exam, even with magnification.

I would say by all means get your Pap smear, which may pick up changes caused by HPV. The exam should include a urine test for both gonorrhea and chlamydia. Get tested for syphilis, HIV and hepatitis B, which will probably all be negative if you have practised safe sex; but I don’t think it is worth it to routinely do the blood tests for herpes. Keep on practicing safe sex until you and your partner are in a long-term monogamous relationship and you both know you don’t have any of the nasty STDs. You may then decide that the other risks are worth taking.

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