13 Signs and Symptoms of Kidney Infection (Pyelonephritis)
Your kidneys are essential for overall health, as they remove toxins from your bloodstream and regulate fluid levels in your body. Bacteria can invade the kidneys and cause an infection (pyelonephritis), presenting warning signs that must be taken seriously.
A kidney infection usually starts as a lower urinary tract infection (UTI) in the bladder and can spread to the kidneys, causing disruptive symptoms. Unlike a typical UTI, a kidney infection is more serious, can lead to complications, and can quickly become dangerous if not treated promptly.
Common Symptoms
Kidney infections cause significant symptoms that often affect both your urinary system and overall health. Most people experience a combination of urinary issues and whole-body effects, which worsen as the infection progresses.
Fever and Chills
Fever and chills are among the most prevalent symptoms and possibly indicate that the infection has reached your kidneys. A fever of 101°F (38.3°C) or higher may develop suddenly, making you feel weak, fatigued, and unwell.
These symptoms show that your immune system is actively fighting the infection. Your body may also respond with shivering and chills, which can alternate with periods of sweating as it tries to regulate body temperature.
If your fever rises rapidly, becomes persistent, or does not respond to over-the-counter fever medications, seek medical attention immediately. This may signal that the infection is worsening or possibly spreading to the bloodstream.
Flank Pain
Flank pain is a key symptom of a kidney infection. It usually occurs on one side of the lower back or side, depending on which kidney is affected.
The discomfort typically starts below the ribs or near the waistline, presenting as a dull, constant ache or intermittent sharp pains that worsen with movement, deep breaths, or when pressure is applied to the affected area.
Unlike typical back pain, flank pain does not improve with rest or posture changes, and tends to persist or worsen if the infection is left untreated.
Painful or Burning Urination
Painful or burning urination (dysuria) can occur with a kidney infection, particularly if the infection begins as a lower urinary tract infection (UTI) and spreads to the kidneys.
You may experience a burning, stinging, or sharp pain when urinating, which may persist even after urination. This results from inflammation and irritation in the urinary tract, making the urethra more sensitive to urine flow.
Some people experience pressure, cramping, or a dull ache in the lower abdomen, along with pain or discomfort during urination.
Frequent Urge to Urinate
You may feel the need to urinate more often than usual, sometimes with a sudden and urgent sensation. Even after urinating, your bladder may feel partially emptied, leading to a constant need to use the toilet.
Despite frequent trips to the bathroom, you may only pass small amounts of urine each time. This symptom occurs because a kidney infection can inflame or irritate the bladder, causing it to signal the need to urinate more frequently.
This symptom can also wake you up multiple times at night (nocturia), disrupting your sleep. In some cases, kidney infections cause only a moderate increase in urination frequency, while in others, the urgency can be just as intense as when the bladder is infected.
Cloudy, Foul-Smelling, or Bloody Urine
A kidney infection can cause noticeable changes in urine color, clarity, and smell. Instead of being clear or light yellow, urine may become cloudy or murky due to the presence of pus, white blood cells, and bacteria.
It may also contain visible particles or sediment, making it thicker than usual. A strong, unpleasant odor is another common sign. Some people notice a foul, ammonia-like, fishy, or sulfuric urine smell caused by bacterial waste products.
Blood in the urine (hematuria) may appear pink, red, or brown, indicating that inflammation or irritation has damaged small blood vessels in the kidneys or urinary tract. Sometimes, the blood is microscopic and not visible, requiring laboratory testing for detection.
Additional Symptoms
A kidney infection can cause symptoms beyond fever and flank pain, affecting digestion, energy levels, and other parts of the abdomen. These additional symptoms may indicate the disease is spreading and impacting multiple systems, potentially signaling a worsening condition.
Fatigue and Weakness
When you have a kidney infection, your body uses extra energy to fight off bacteria, leaving you physically and mentally exhausted. Fatigue may start as mild tiredness but can become severe and persistent, making it difficult to complete tasks and activities.
You may still wake up feeling drained and sluggish despite needing extra sleep due to the effects of the infection and the other symptoms experienced.
Weakness often accompanies fatigue, making movements harder and causing difficulty standing for long periods, lifting objects, or climbing stairs due to muscle fatigue.
Nausea and Vomiting
Nausea and vomiting can occur with a kidney infection, though they are not always present. These symptoms arise from the body’s systemic response to infection and inflammation, which can affect the gastrointestinal system.
Nausea may begin mildly and progress, making eating or drinking difficult. Vomiting may follow, potentially leading to dehydration if fluid deficiency is not addressed. Dehydration can further strain kidney function and worsen symptoms.
Lower Abdominal or Pelvic Pain
Pain from a kidney infection can spread from your back to the lower abdomen or pelvic region, causing aching, pressure, or tenderness above your pubic bone. This discomfort occurs due to inflammation affecting the nearby structures.
The discomfort can be constant, enough to cause disruption to your sleep and activities when awake, while aching can be sharp and spasmodic, similar to menstrual cramps.
Some individuals may also experience stomach bloat or a sensation of fullness around that area, which could be linked to urinary retention or bladder irritation.
This discomfort is often accompanied by other worsening urinary symptoms and can significantly impact daily life, leading to anxiety and distress.
Severe Symptoms
When kidney infections become severe, they can lead to life-threatening complications that require emergency medical care. Prompt and early recognition of these symptoms is critical to preventing serious health consequences.
High Fever with Uncontrollable Chills
A fever above 103°F (39.4°C) with intense chills can indicate a severe kidney infection. The fever may start mildly but can rapidly escalate and become difficult to manage, sometimes resisting fever-reducing medications.
As the fever subsides, the body reacts with violent chills and shaking to increase internal temperature. These episodes can last several minutes, recur frequently, and are often followed by profuse sweating as the body attempts to regulate its temperature.
This cycle can be both exhausting and disorienting, leaving individuals feeling drained and vulnerable. It’s essential to stay hydrated and monitor symptoms closely during such times.
Severe Flank Pain
If the flank pain becomes intense, persistent, and difficult to manage, this may signal a worsening infection or kidney injury.
The pain can spread to your abdomen, groin, or upper back and often feels deep and unrelenting, rather than a typical backache.
You may experience sharp, stabbing, or pressure-like pain, making it hard to find a comfortable position. As the infection advances, the kidney may become swollen or develop abscesses, leading to severe tenderness.
Gentle tapping over the kidney area can intensify the pain, indicating worsening inflammation. Over-the-counter pain relievers are often ineffective for severe pain and require urgent medical treatment.
Confusion or Brain Fog
A sudden change in mental state can indicate that a kidney infection has become severe or progressed to sepsis. You may experience difficulty concentrating, memory problems, slowed thinking, trouble forming sentences, or difficulty following conversations.
Confusion occurs when bacteria from the kidneys spread into the bloodstream (bacteremia), triggering inflammation that disrupts brain function. In older adults, confusion may be the first or only symptom of a severe kidney infection, often mistaken for dementia or delirium.
Family members may notice unusual behavior, difficulty responding to questions, forgetfulness, and frequently losing personal items, in addition to sudden personality changes.
If confusion persists or worsens, seek immediate medical care, as it may indicate a severe infection or a negative reaction of the immune system needing urgent treatment.
Rapid Pulse
A rapid heart rate (tachycardia) above 100 beats per minute at rest can be a severe symptom of pyelonephritis. This happens as the body fights the infection, increasing circulation to deliver more oxygen and immune cells.
You may feel a racing or pounding heartbeat in your chest, neck, or temples. This can occur suddenly or persist throughout the day, often worsening with movement, when standing up, or during stressful situations.
Tachycardia is frequently accompanied by shortness of breath, dizziness, and weakness. In severe cases, you may experience cold, clammy skin, confusion, or fainting, which could indicate septic shock, a life-threatening condition.
Low Blood Pressure
If you develop low blood pressure from a kidney infection, it is considered a critical emergency that can quickly escalate to septic shock, a life-threatening condition caused by severely impaired circulation.
This occurs when bacteria enter the bloodstream and trigger widespread inflammation, which dilates blood vessels and reduces blood flow. You may feel dizzy, unsteady, or even black out, especially when standing up suddenly (postural hypotension).
As circulation weakens, symptoms may worsen, leading to cold skin, a pale complexion, and extreme weakness due to insufficient oxygen delivery. Without immediate medical treatment, septic shock can lead to multiple organ failure and quickly become fatal.
