A kidney infection doesn’t typically cause leg pain directly, but it can in certain situations. The pain most commonly associated with a kidney infection sits in the lower back or flank, below the rib cage on one or both sides. However, the infection can produce referred pain that travels to the groin, inner thigh, or upper leg. In rare but serious cases, the infection can spread to a nearby muscle and cause significant leg pain that makes walking difficult.
How Kidney Infections Cause Referred Pain
Your kidneys share nerve pathways with other parts of your lower body. When a kidney becomes inflamed or infected, those nerves can send pain signals that your brain interprets as coming from somewhere else, like your groin, pelvis, or upper thigh. This is called referred pain, and it’s the same reason a heart attack can cause arm pain even though nothing is wrong with the arm itself.
Research into urinary tract infections has revealed that infection-driven inflammation can trigger a process called central sensitization, where the spinal cord essentially becomes “turned up” in how it processes pain signals. This heightened state can cause skin sensitivity and discomfort in areas far from the infection site, including the pelvic region and lower extremities. Pain receptors involved in this process can both initiate and maintain chronic discomfort even as the infection itself is being treated.
Kidney stones, which sometimes accompany or are confused with kidney infections, are more likely to produce pain that clearly radiates from the flank down toward the groin. If you’re feeling pain that seems to travel from your side down into your inner thigh or groin area, a kidney stone could be involved alongside or instead of an infection.
When Infection Spreads to the Psoas Muscle
The more concerning way a kidney infection causes leg pain is by spreading to the psoas muscle. This large muscle runs along either side of your spine and connects to your upper thigh bone, playing a key role in hip flexion and walking. When a urinary tract infection travels into this muscle, it can form a pocket of pus called a psoas abscess.
A psoas abscess can produce thigh pain severe enough to cause limping. In one documented case, a patient with a urinary tract infection developed such intense pain in her thigh that she couldn’t walk normally. Even passive movement of her leg made the pain worse. Other signs of a psoas abscess include vague abdominal or back pain, fever, nausea, painful urination, fatigue, and weight loss. People who are immunocompromised are at higher risk for this complication.
This is uncommon, but it’s worth knowing about because a psoas abscess can easily be mistaken for a simple back or leg problem. If you have a known or suspected kidney infection and develop worsening leg or thigh pain, especially with a limp or pain during hip movement, that combination of symptoms needs prompt medical evaluation.
Telling Kidney Pain Apart From Back or Leg Problems
Kidney-related pain and musculoskeletal pain like sciatica can feel similar, but they behave differently. Kidney pain tends to sit deep in the flank below your ribs, often on one side. It may be sharp and come in waves or feel like a constant dull ache. It doesn’t usually change with movement or position.
Back and leg pain from a slipped disc or sciatica, by contrast, tends to worsen when you bend, lift, twist, or sit. It often produces shooting or stabbing sensations and may come with numbness or tingling down the leg. The pain typically follows a path from the lower back through the buttock and down one leg.
The clearest distinguishing factor is what accompanies the pain. Kidney infections almost always come with additional urinary symptoms: a frequent or urgent need to urinate, burning during urination, cloudy or bloody urine, fever, nausea, or vomiting. If your leg pain comes with any of these, the kidneys are a more likely culprit than a muscle or nerve issue. Pure musculoskeletal problems rarely cause fever or urinary changes.
How Doctors Check for Kidney Involvement
One of the simplest physical tests is checking for costovertebral angle tenderness. A doctor places a hand on your back just below the ribs on each side and taps it with the other fist. If this produces a sharp spike of pain, particularly on one side more than the other, it strongly suggests kidney involvement. Urine tests and blood work can then confirm whether an infection is present, and imaging may be ordered if a complication like an abscess is suspected.
Signs the Infection Is Becoming Serious
Most kidney infections respond well to antibiotics, with symptoms beginning to improve within a few days of starting treatment. Full courses typically last a week or longer. But a kidney infection that goes untreated or doesn’t respond to medication can progress to sepsis, a life-threatening condition where the infection enters the bloodstream.
Warning signs of sepsis include a high heart rate or weak pulse, confusion or disorientation, extreme pain, fever with shivering or feeling unusually cold, shortness of breath, and clammy or sweaty skin. If you have a kidney infection and develop any of these symptoms, or if your symptoms are getting worse rather than better, that requires emergency care. Leg pain that suddenly worsens or appears alongside these systemic symptoms is especially concerning, as it could indicate the infection is spreading beyond the kidney.
What to Expect During Recovery
Once antibiotics are started for a kidney infection, most people notice their fever dropping and pain easing within two to three days. Referred pain in the groin or thigh typically follows the same timeline, fading as the kidney inflammation subsides. If a psoas abscess has formed, treatment takes longer and may require drainage in addition to antibiotics.
Leg pain that persists or worsens after several days of antibiotic treatment is a signal that something else may be going on, whether that’s an abscess, a kidney stone complicating the infection, or an unrelated musculoskeletal problem that was coincidentally timed. Persistent pain after treatment warrants follow-up imaging to rule out complications.