What STDs Cause Blood in Urine and Why It Happens

Several sexually transmitted infections can cause blood to show up in your urine, most commonly chlamydia and gonorrhea, though trichomoniasis, genital herpes, and even HPV have been linked to it as well. The blood almost always traces back to one thing: inflammation. When an STI infects the urethra, cervix, or surrounding tissue, the irritated lining can bleed, and that blood mixes with urine on its way out. The picture is more complicated than a simple checklist, though, because blood in urine has dozens of possible causes, and figuring out whether an STI is responsible takes more than a standard urinalysis.

Chlamydia and Gonorrhea Are the Most Common STI-Related Causes

Chlamydia (caused by Chlamydia trachomatis) and gonorrhea (caused by Neisseria gonorrhoeae) are the two infections most frequently tied to blood in urine. Both organisms target the urethra, and urethritis is the hallmark of each infection in men and a frequent manifestation in women.¹ When the urethral lining becomes inflamed, small blood vessels in the tissue can break. Blood then mixes with urine during urination, sometimes producing a pinkish or rust-colored stream, sometimes only detectable under a microscope.

Gonorrhea tends to cause more dramatic symptoms than chlamydia. A thick, yellowish-green discharge and burning during urination are classic signs, and visible blood in the urine or discharge is not unusual. Chlamydia, on the other hand, is often called the “silent” infection because many people have no symptoms at all. When chlamydia does produce blood in the urine, it may be the only noticeable sign that something is wrong, which makes it easy to blame on a urinary tract infection instead.

A retrospective study of young men with urethritis-like symptoms found that among those whose standard urinalysis and urine culture came back negative, about 30% were later diagnosed with gonorrhea or chlamydia through more sensitive molecular testing. Discharge turned out to be the strongest predictor, but many patients had no discharge at all and were still infected.² That finding underscores a recurring theme: these infections can be present and causing subtle urinary tract irritation even when the classic red flags are absent.

Trichomoniasis

Trichomoniasis, caused by the parasite Trichomonas vaginalis, is the most common curable STI worldwide and another established cause of blood in the urine. In women, the parasite infects the vagina and cervix, where it can trigger enough inflammation to produce a frothy, greenish discharge tinged with blood. The cervix sometimes develops a distinctive spotted appearance sometimes called a “strawberry cervix” because of its punctate red dots, though this shows up in only about 10% of cases on a routine exam.³ When the cervix or vaginal walls are inflamed and bleeding, blood can easily mix with urine during urination, giving the appearance of hematuria.

In men, trichomoniasis usually infects the urethra and can cause a mild burning with urination or a thin discharge. Frank blood in the urine is less common in men but still possible. One complication with trichomoniasis is that many infected people, particularly men, have no symptoms for weeks or months. By the time blood shows up, the infection may have been quietly present for a while.

Genital Herpes and the Urinary Tract

Genital herpes, caused by herpes simplex virus (usually HSV-2, sometimes HSV-1), is best known for painful blisters around the genitals. But the virus can also infect the urethra directly. Researchers have detected HSV in urethral swabs and first-voided urine from men with acute urethritis who had no visible herpes sores at all.⁴ When herpes causes urethritis, the inflammation can produce dysuria, discharge, and occasionally blood in the urine.

In women, herpes outbreaks near the urethral opening can make urination extremely painful, and open sores in that area may bleed when urine passes over them. This is technically blood mixing with urine from an external source rather than bleeding inside the urinary tract, but the practical effect for the person is the same: they see blood when they urinate. During a first herpes outbreak, which tends to be the most severe, this symptom can be alarming enough to prompt an emergency room visit.

Less Familiar Infections That Can Be Involved

Mycoplasma genitalium is a bacterium that has only gained widespread clinical attention in the last couple of decades. It is now recognized as a cause of both acute and chronic urethritis in men, and evidence suggests it can also cause cervicitis and pelvic inflammatory disease in women.⁵ Because it triggers the same kind of urethral inflammation as chlamydia or gonorrhea, it can also lead to blood appearing in the urine. The tricky part is that many clinics do not routinely test for it, so a person could be treated for a “non-specific urethritis” without the underlying organism ever being identified.

Human papillomavirus, better known for causing genital warts and cervical cancer, does not typically cause urinary symptoms. In rare cases, though, HPV can affect the urethra or even the bladder lining. One documented case involved a young woman with persistent lower urinary tract symptoms whose biopsy revealed HPV-related changes in the bladder wall itself, along with warts near the urethral opening.⁶ Cases like this are uncommon, but they illustrate that when standard testing comes back negative and urinary symptoms persist, less obvious infections should be on the radar.

How STIs Actually Produce Blood in Urine

The unifying mechanism is inflammation. The urethra, cervix, and surrounding mucosal tissues are lined with thin, well-vascularized membranes. When a pathogen colonizes these surfaces, the immune system responds by flooding the area with white blood cells, dilating small blood vessels, and releasing chemical signals that increase tissue permeability. The membrane becomes swollen, fragile, and prone to micro-bleeding. As urine passes through an inflamed urethra, it picks up red blood cells shed from those damaged surfaces.

In some cases, the infection produces actual ulceration. Herpes sores, syphilitic chancres, and the lesions of less common infections like donovanosis can all erode the mucosal surface deeply enough to bleed on contact. A study of women with genital ulcer disease in South Africa found that bleeding was observed from the ulcers of 59 patients during specimen collection, spanning infections including syphilis, herpes, donovanosis, and chancroid.⁷ If those ulcers are near the urethral opening, blood readily enters the urine stream. The amount can range from microscopic traces detectable only with a dipstick to visible red or brown discoloration.

Women face an additional wrinkle. Because the urethra, vagina, and cervix are in close proximity, cervical or vaginal bleeding from an STI can mix with urine during urination even though the urinary tract itself is not infected. A person may report blood in the urine when the actual source is the cervix. This anatomical overlap is one reason clinicians often need a pelvic exam, not just a urine test, to sort out what is actually going on.

Why a Routine Urine Test Can Miss STIs Entirely

Many people assume that if they give a urine sample and it comes back “normal,” they do not have an infection. That assumption is dangerously wrong when it comes to STIs. A standard urinalysis looks for bacteria, white blood cells, and other signs of a typical urinary tract infection. It is not designed to detect chlamydia, gonorrhea, trichomoniasis, or any other sexually transmitted pathogen. Research has confirmed that infections with T. vaginalis, N. gonorrhoeae, and C. trachomatis were not associated with a positive urine culture in emergency department patients.⁸ In other words, a person could walk in with an active gonorrhea infection causing urethritis and blood in the urine, and their urine culture could still read as negative.

Detecting these infections requires nucleic acid amplification testing, commonly called NAAT, which searches for genetic material from the specific organisms. NAAT is highly sensitive and can be run on a urine sample, but the clinician has to order it explicitly. In the study of young men with urethritis-like symptoms mentioned earlier, nearly a third of those with negative standard urine tests were found to have gonorrhea or chlamydia once NAAT was performed.² If you are experiencing blood in your urine and there is any possibility of an STI, ask specifically for STI testing rather than assuming a basic urinalysis will catch everything.

How to Tell If Blood in Urine Is from an STI or Something Else

Blood in the urine, medically called hematuria, has a long list of possible causes that have nothing to do with sexual activity. Kidney stones, bladder infections, vigorous exercise, certain medications, and even eating beets can produce pink or red urine. In older adults, hematuria can sometimes signal bladder or kidney cancer. So seeing blood does not automatically mean you have an STI.

A few features make an STI-related cause more likely:

Discharge: Any urethral or vaginal discharge, especially if it is colored or has an odor, raises the probability of an STI over a simple urinary tract infection.
Pain during sex: Dyspareunia alongside bloody urine points toward a genital infection rather than a kidney or bladder problem.
Recent unprotected contact: A new partner or unprotected encounter within the past few weeks makes STI testing a priority.
Absence of typical UTI bacteria: If a urine culture is negative but symptoms persist, an STI should be considered before assuming the sample was contaminated.

None of these features is definitive on its own, but when several appear together, they paint a clearer picture. A clinician evaluating blood in urine will often check for both UTI and STI simultaneously if the history suggests sexual transmission is possible.

When the STI Is Not in the Urethra at All

Most discussions of STIs and bloody urine focus on urethritis, but in women, infections higher in the reproductive tract can also be responsible. Pelvic inflammatory disease, which occurs when bacteria like chlamydia or gonorrhea ascend from the cervix into the uterus and fallopian tubes, can occasionally produce hematuria. A systematic review of PID cases in pediatric and adolescent patients noted that while lower abdominal pain and fever were the dominant symptoms, one patient presented with macroscopic hematuria as a notable finding.⁹ PID-related hematuria is uncommon, but it illustrates that an STI’s effects are not always confined to the spot where the organism first took hold.

Syphilis is another example. A primary syphilitic chancre on or near the genitals can bleed, and in a study of women with genital ulcer disease, syphilis was diagnosed in 40% of patients, making it the single most common cause of genital ulceration in that population.⁷ A bleeding chancre near the urethral meatus could easily be mistaken for blood in the urine, especially if the sore is painless and goes unnoticed, as primary syphilis chancres often are.

Why Symptoms Can Lag Behind Infection

One pattern that catches people off guard is the delay between exposure and symptoms. Chlamydia can incubate for one to three weeks before producing any sign of trouble, and gonorrhea typically takes two to five days but can take longer. Trichomoniasis has an incubation window that ranges from a few days to nearly a month. Herpes outbreaks can appear within days of exposure or lie dormant for months before the first flare. So if blood in your urine appeared weeks after a sexual encounter, that does not rule out an STI. In fact, the delay is the norm rather than the exception.

Conversely, not every STI will eventually produce bloody urine. Most chlamydia infections, for example, cause no visible bleeding. The likelihood depends on the organism, the severity of inflammation, and individual anatomy. People with shorter urethras (generally women) may notice blood more readily because the inflamed area is closer to the external opening, but they may also confuse vaginal bleeding with urinary bleeding. People with longer urethras (generally men) are less likely to see gross blood but may still have microscopic hematuria detectable on a dipstick test.

Getting Tested and What to Expect

If you suspect an STI is behind blood in your urine, the most useful step is requesting a comprehensive STI panel rather than relying on a basic urine test. In most clinics, this means a NAAT test for chlamydia and gonorrhea at minimum. Testing for trichomoniasis may require a separate test, and Mycoplasma genitalium testing is not yet standard everywhere, so you may need to ask for it by name. Herpes is typically diagnosed by clinical examination of lesions or by a type-specific blood test rather than a urine test.

If your STI tests return positive, the reassuring news is that the most common culprits are treatable. Chlamydia and gonorrhea respond to antibiotics, though gonorrhea’s rising resistance to certain drugs means your provider may use a specific regimen. Trichomoniasis is curable with a single course of antiparasitic medication. Mycoplasma genitalium can be harder to treat because resistance to first-line antibiotics is growing, but it is still manageable with the right drug combination. Once the infection clears, the inflammation subsides, and the blood in the urine resolves along with it.

If STI testing and standard cultures are both negative but blood persists, further evaluation is warranted. Depending on your age, sex, and risk factors, a clinician may consider imaging of the kidneys and bladder, a cystoscopy to look at the bladder lining directly, or testing for rarer conditions. Persistent unexplained hematuria should never be brushed off as “probably nothing,” because in a small percentage of cases it can point to something that needs prompt attention.

Co-Infections and Compounded Risk

Having one STI makes you more likely to have another simultaneously. Chlamydia and gonorrhea are frequently found together, and either one can coexist with trichomoniasis or herpes. Co-infection matters because each pathogen adds its own inflammatory burden, which can amplify symptoms like bleeding. The case study of a 27-year-old man with simultaneous gonorrhea and a parasitic co-infection is an unusual example, but the general principle applies broadly: when multiple organisms are attacking the urethral lining at once, tissue damage is worse and symptoms like hematuria become more likely.¹

Co-infection also complicates diagnosis. If a clinician tests for gonorrhea, finds it, treats it, and the blood in the urine improves but does not fully resolve, a second pathogen may be lurking. This is one reason comprehensive panels that test for multiple organisms at once are more efficient than a stepwise approach. Treating everything present in a single round prevents the frustrating cycle of partial improvement followed by relapse.

1
Die Urologie. Urethritis due to coinfection with Neisseria gonorrhoeae and Enterobius vermicularis in a 27-year-old man
2
Scientific Reports. Diagnosis and treatment outcomes of urethritis-like symptoms in young males: a retrospective cohort study
3
Scientific Archives. Strawberry Cervix- A Clinical Image of Trichomonas vaginalis: A Case Report
4
ScienceDirect. Clinical courses of herpes simplex virus-induced urethritis in men
5
PubMed Central. Mycoplasma genitalium: should we treat and how?
6
PubMed Central. Human papillomavirus infection causing refractory lower urinary tract symptoms in a young female
7
PubMed Central. Genital ulcer disease in women in Durban, South Africa
8
PubMed Central. Association Between Sexually Transmitted Infections and the Urine Culture
9
PubMed Central. Diagnostic Challenges and Management Strategies of Pelvic Inflammatory Disease in Sexually Inactive Pediatric and Adolescent Patients: A Systematic Review of Case Reports