Yes, pyelonephritis commonly causes hematuria (blood in the urine). In young women with acute pyelonephritis, up to 40% develop visible blood in their urine, and microscopic hematuria, detectable only on a lab test, is even more common. Blood in the urine is not the hallmark symptom of a kidney infection, but it is a frequent one, and understanding why it happens and how long it lasts can save you a lot of worry.
Why a Kidney Infection Causes Bleeding
Pyelonephritis is a bacterial infection that reaches the kidney, usually after bacteria travel up from the bladder through the ureter. Once bacteria establish themselves in kidney tissue, the immune system launches an intense inflammatory response. White blood cells flood the area, and the delicate blood vessels lining the kidney’s filtering units and collecting system become swollen and damaged. Red blood cells leak through those compromised vessel walls and end up in the urine.
The infection can also directly erode the lining of the renal pelvis and ureters, adding another source of bleeding. This is the same basic process that causes bleeding in a simple bladder infection, but because the kidney has a much richer blood supply than the bladder wall, pyelonephritis can produce more noticeable blood in the urine.
Microscopic vs. Visible Blood
Hematuria from pyelonephritis shows up in two forms. Microscopic hematuria means red blood cells appear on a urinalysis but the urine still looks normal to the naked eye. This is the more common pattern and is considered a routine finding in kidney infections. Gross hematuria, where urine turns pink, red, or cola-colored, is more striking but still occurs in a significant minority of cases. That 40% figure for gross hematuria applies mainly to younger women; it is much less common in men with the same infection.
Seeing visible blood in your urine during a kidney infection does not automatically mean the infection is more severe. However, if hematuria is present, clinicians also consider whether a kidney stone could be contributing, since stones and infections sometimes occur together and both independently cause bleeding.
Other Symptoms That Accompany Hematuria
Blood in the urine rarely appears as the only sign of pyelonephritis. The classic combination includes fever (often above 101°F), flank pain on one or both sides, nausea or vomiting, and general malaise. Many people also have lower urinary tract symptoms like burning with urination, urgency, and frequency, especially if the infection started as a bladder infection that ascended to the kidney. A urinalysis typically also shows bacteria and a high number of white blood cells alongside the red blood cells.
How Long Hematuria Lasts After Treatment
One of the most practical questions is when the blood in your urine should clear up. The answer is slower than most people expect. A study tracking hematuria resolution after urinary tract infections found that only 38% of patients had clear urinalyses at 30 days. The median time to resolution was about 60 days, and 25% of patients still had microscopic blood at the six-month mark. Because of this slow timeline, repeat urine testing is generally recommended around 12 weeks after treatment rather than sooner. Testing too early can lead to unnecessary concern or additional workups for hematuria that would have resolved on its own.
If you finish a full course of antibiotics and still notice pink or red urine weeks later, that timeline alone is not a red flag. Persistent microscopic hematuria beyond six months, on the other hand, warrants further evaluation to rule out other causes.
When Hematuria Points to Something Else
Several conditions share the combination of flank pain and blood in the urine, so hematuria during what seems like a kidney infection is not always caused by the infection alone. Kidney stones are the most common overlap: a stone can obstruct urine flow and create conditions that promote infection while also scratching the ureter lining and causing bleeding independently. Other possibilities include blood clots in the kidney’s blood vessels, IgA nephropathy (a type of kidney inflammation unrelated to infection), and, rarely, kidney tumors or cysts.
A condition called loin pain hematuria syndrome can mimic pyelonephritis with ongoing flank pain and blood in the urine, but it persists for months without evidence of infection or stones. Nutcracker syndrome, where a vein near the left kidney gets compressed, can also cause left-sided flank pain with hematuria. These are uncommon, but they are worth knowing about if symptoms keep returning without a clear infectious cause. Imaging with CT and sometimes cystoscopy (a camera exam of the bladder) helps sort out these possibilities.
Severe Infections and Hematuria
In most cases, hematuria from pyelonephritis resolves with standard antibiotic treatment. But a rare and dangerous form of kidney infection called emphysematous pyelonephritis, where gas-forming bacteria destroy kidney tissue, lists hematuria among its presenting signs along with high fever, flank pain, and rapid deterioration toward sepsis or shock. This condition can lead to kidney abscesses, acute kidney failure, and multi-organ failure. It occurs most often in people with uncontrolled diabetes or urinary tract obstruction. The key difference from ordinary pyelonephritis is how sick the person looks and how quickly they worsen, not the hematuria itself.
For typical acute pyelonephritis, blood in the urine is a common, expected finding that resolves gradually over weeks to months. Watching it persist during recovery is unsettling but normal, as long as your other symptoms (fever, pain, feeling unwell) are improving with treatment.