Urine that’s unexpectedly bloody warrants a trip to the hospital or emergency room. Flu-like symptoms may also be a sign of severe infection, so it’s important to seek medical care. Prompt diagnosis and treatment can help reduce the risk of long-term complications.

Most UTIs affect the lower urinary tract, which is made up of the urethra and bladder. This usually results in localized symptoms related to urination.

However, if left untreated, lower UTIs can migrate to the upper portion of the urinary tract. Upper UTIs cause systemic, flu-like symptoms, such as malaise, fever, chills, vomiting, nausea, and back or side pain.

“An upper UTI can also lead to blood in your urine,” says Monte Swarup, MD, OB-GYN, founder of the health information site HPV HUB.

These symptoms warrant a visit to the emergency room because they suggest that the infection has overtaken the kidneys, says Jill Krapf, MD, OB-GYN, with The Center for Vulvovaginal Disorders in Tampa, Florida.

She notes that medical attention is especially important if you’re at risk for a complicated UTI. This includes people who:

According to Krapf, you can expect a combination of the following:

“If you’re diagnosed with a UTI in the ER, the doctor will determine the appropriate treatment based on the severity of the infection,” she says.

Mild cases can usually be resolved with oral antibiotics. “For more severe infections, treatment may involve hospitalization and intravenous (IV) antibiotics,” explains Krapf.

To be clear: If you have symptoms of a UTI, you should seek medical care. Following the prescribed treatment plan is important if your clinician diagnoses a UTI.

“Left undiagnosed and untreated, a UTI can lead to medical issues that are more serious, such as kidney damage, kidney scarring, and sepsis,” says Swarup. Sepsis can be fatal if left untreated.

In some cases, bladder or prostate damage can also occur.

Some symptoms of UTIs — such as upper back pain, vomiting, blood in your urine, fever, and chills — warrant immediate medical attention.

Left untreated, UTIs can progress, leading to serious, sometimes permanent, side effects.

Gabrielle Kassel (she/her) is a queer sex educator and wellness journalist who is committed to helping people feel the best they can in their bodies. In addition to Healthline, her work has appeared in publications such as Shape, Cosmopolitan, Well+Good, Health, Self, Women’s Health, Greatist, and more! In her free time, Gabrielle can be found coaching CrossFit, reviewing pleasure products, hiking with