Urine during a kidney infection typically looks cloudy or milky and may appear pink, red, or brown if blood is present. It often smells noticeably foul. These changes happen because your body is flooding the urinary tract with infection-fighting white blood cells, and the kidneys themselves may be inflamed enough to leak small amounts of blood.
Cloudy or Milky Urine
The most common visible change is cloudiness. Normal urine is pale yellow and mostly transparent. When bacteria infect your kidneys, your immune system sends large numbers of white blood cells to the area, and those cells end up in your urine. This is called pyuria, and it’s what gives urine that milky, opaque look. Mucus and protein from the inflamed kidney tissue can add to the haze.
Cloudiness from a kidney infection tends to be more persistent and pronounced than the slight cloudiness you might see from dehydration or eating certain foods. If your urine consistently looks like diluted milk or has visible particles floating in it, that’s a strong signal something is going on beyond a simple hydration issue.
Pink, Red, or Brown Tones
Blood in the urine is common with kidney infections. When there’s enough blood to see with the naked eye (called gross hematuria), urine can range from faintly pink to deep red or even brownish, similar to cola or iced tea. The shade depends on how much blood is present and how concentrated your urine is at the time.
A light pink tint means a relatively small amount of blood is mixing in. Darker red or brown urine means more blood, or that the blood has had time to break down as it travels from the kidney through the ureter to the bladder. Brown or tea-colored urine in particular suggests the bleeding originates higher up in the urinary tract, closer to the kidneys, rather than in the bladder or urethra.
Not everyone with a kidney infection will see visible blood. Sometimes blood is only detectable under a microscope during a urinalysis. But if you do notice a color shift toward pink, red, or brown alongside other symptoms, it’s worth taking seriously.
Strong or Foul Smell
Kidney infection urine frequently smells bad. The odor comes from bacteria multiplying in the urinary tract and from the waste products those bacteria produce. Some people describe it as sharp, ammonia-like, or simply unpleasant in a way that’s clearly different from normal urine. The smell can be stronger if you’re also dehydrated, since less water in the urine means a higher concentration of everything causing the odor.
Darker Color From Fever and Dehydration
Kidney infections almost always cause fever, and fever drives dehydration. When you’re dehydrated, your kidneys conserve water by producing less urine that’s more concentrated. This makes urine darker, often deep amber or honey-colored, on top of any cloudiness or blood that’s already present.
The combination can be striking: urine that is simultaneously dark, cloudy, and foul-smelling. You may also notice you’re urinating less frequently or producing smaller amounts than usual. Higher fevers tend to cause more severe dehydration, which intensifies all of these changes. Drinking fluids helps dilute the urine somewhat, but won’t resolve the underlying infection.
How It Differs From a Bladder Infection
A lower urinary tract infection (bladder infection) can also cause cloudy or smelly urine, so the urine changes alone don’t tell you exactly where the infection is. The key difference is what’s happening in the rest of your body. Bladder infections typically cause burning with urination, frequent urges to pee, and lower abdominal discomfort, but you generally feel okay otherwise.
Kidney infections layer on systemic symptoms: fever (often above 101°F), chills, nausea or vomiting, and pain in your back or side, usually just below the ribs on one side. If your urine looks off and you also feel like you have the flu with back pain, that pattern points toward kidney involvement rather than a simple bladder infection. Some people initially have bladder infection symptoms that worsen over a few days as bacteria travel upward to the kidneys.
What Doctors Look For in Your Urine
When you bring a urine sample in, a dipstick test checks for two main markers. One detects white blood cells (a sign of inflammation), and the other detects nitrites, which are produced when certain common bacteria like E. coli break down compounds in your urine. A result showing high levels of white blood cells plus positive nitrites is considered a strong positive for infection.
Under a microscope, kidney infections show something bladder infections typically don’t: white blood cell casts. These are clumps of white blood cells that formed inside the tiny tubes of the kidney and got flushed out. Their presence is a specific marker that the infection has reached the kidneys. Small amounts of protein in the urine are also common during a kidney infection, since inflammation disrupts the kidney’s normal filtering.
When Urine Changes Signal Something Urgent
A significant drop in urine output is the change that matters most in terms of severity. If you notice you’re barely urinating, or your urine output drops sharply over several hours, it can signal that the infection is putting strain on your kidneys. In severe cases, a kidney infection can progress to a bloodstream infection (sepsis), and one of the earliest signs of kidney injury from sepsis is producing very little urine. Research shows that even a few hours of significantly reduced urine output during sepsis is associated with kidney injury.
Other red flags alongside unusual-looking urine include a fever that won’t come down, confusion, rapid heartbeat, or worsening back pain. The combination of very dark, scant urine with high fever and feeling severely ill suggests the infection may be overwhelming your body’s ability to manage it, and that’s a situation that needs emergency care rather than a wait-and-see approach.