Kidney Infection (Pyelonephritis)

Reviewed on 10/26/2022

Things to Know About a Kidney Infection (Pyelonephritis)

Common symptoms of a kidney infection are nausea, fatigue, and dull lower back pain.
  • The kidneys are a component of the urinary system, which also includes the ureters, urinary bladder, urethra, and prostate (in men). The kidneys are located on either side of the middle back and under the diaphragm. The main functions of the kidneys include filtering the waste products from the body, regulating blood pressure, maintaining the normal concentration of electrolytes (sodium, calcium, potassium, magnesium, etc.) in the body, and contributing to the production of blood cells.
  • The urine is drained downward from each kidney into the ureters, which are thin, tube-like structures that connect the kidneys to the bladder. The urine, then, drains from the bladder via another tube-like structure, called the urethra, and exits the body.
  • Kidney infections belong to the family of infections of the urinary system called urinary tract infections (UTIs). In general, the infection of the urethra, bladder, and prostate is known as a lower urinary tract infection. When the infection ascends to involve the kidneys, then it is called an upper urinary tract infection. Infection of the kidney(s) is also known as pyelonephritis.
  • Urinary tract infections are very common and may affect 40% of women and 10% of men in their lifetime. They are most common in women younger than 50 years of age, whereas, they are rare in men of the same age group. Urinary tract infections are also common in children and may be difficult to diagnose because the symptoms are not easily recognizable. In children, urinary tract infections may be seen more frequently in boys less than 1 year of age and girls less than 4 years of age.
  • In chronic (long-standing) kidney infections, the symptoms may be milder, but more long-lasting.
  • The most important test in diagnosing kidney infection is a urinalysis (UA).
  • The most important component of the treatment of kidney infection is the prompt administration of antibiotics.
  • Rarely, serious complications from a kidney infection occur.

What are Symptoms and Signs of Kidney Infections in Men and Women?

Some of the more common symptoms of kidney infection are:

  1. fever,
  2. chills,
  3. nausea,
  4. vomiting,
  5. generalized weakness,
  6. fatigue,
  7. a burning sensation with urination (dysuria),
  8. dull pain on the side or lower back pain (dull kidney pain), and
  9. dehydration.

In addition to a comprehensive history and physical examination, the signs that a doctor may look for in evaluating for urinary tract infection may include:

  1. tenderness on the flanks immediately below the lowest rib (costo-vertebral angle tenderness),
  2. fever,
  3. physical evidence of dehydration, and
  4. a rapid heart rate.

In women, a pelvic exam may be necessary in order to rule out other similar conditions, such as pelvic inflammatory disease (PID).

In chronic (long-standing) kidney infections, the symptoms may be milder, but more long-lasting.

What Causes Kidney Infections in Children, Men, Women, and During Pregnancy?

  • Kidney and urinary tract infections may be caused by bacteria invading the urine, which is normally a sterile body fluid. Bacteria most commonly gain access to the urine through the urethra, which can be exposed to bacteria from outside of the body.
  • Common sources of bacteria that enter the urinary system are the vagina, anus, and skin. Because of the shorter length of the urethra in women, urinary tract infections are more common in women compared to men. Some factors may predispose certain people to urinary tract infections.
  • Sexual intercourse may increase the risk of urinary tract infections in women. Kidney infection may be facilitated by the introduction of bacteria from outside (vagina) to the urinary system through the urethra.
  • Pregnant women may be at higher risk for developing urinary tract infections. This may be caused by increased pressure on the ureters from the enlarged uterus. Approximately 10% of pregnant women may develop kidney and urinary tract infections during their pregnancy.
  • Kidney stones are another factor that may increase the likelihood of urinary tract infection. Stones can cause partial or complete obstruction to the flow of urine from the kidneys and ureters. This obstruction may act as a focus of infection in the urinary system, leading to urinary tract infections.
  • Bladder catheters (Foley catheters) are sometimes placed into the bladder in order to aid the outflow of urine from the bladder. There are many uses for bladder catheters, for example, paralysis with nerve damage, bladder obstruction from an enlarged prostate, or immobilized or hospitalized patients who are not able to independently urinate. These catheters may act as a vehicle for bacteria to gain access to the urine inside the bladder causing urinary infections.
  • In children, some risk factors include female gender, an uncircumcised male, or a structural abnormality of the urinary system.
  • The most common bacteria causing urinary tract infections or kidney infections are those that are normally seen in the vagina, gastrointestinal tract, or skin. By far, the most common organism causing urinary tract infection is Escherichia coli (E. coli), responsible for up to 80% of kidney and urinary infections. Other common bacteria include Klebsiella, Proteus, Pseudomonas, Enterococcus, and Staphylococcus saprophyticus.

When Should You Go to the Hospital or Doctor If You Think You Have a Kidney Infection?

If symptoms suggestive of a urinary tract or kidney infection are present, medical attention should be sought. Correct diagnosis of kidney infection is important because it will determine the appropriate therapy and length of treatment.

Once the doctor diagnoses kidney infection, home therapy with antibiotics and adequate oral intake of food and fluid may be adequate. In severe cases of infection or uncontrolled nausea and vomiting, hospitalization may be necessary.

What Procedures and Tests Diagnose Kidney Infections in Men and Women?

The most important test in diagnosing kidney infection is a urinalysis (UA). Urinalysis is a test to analyze urine samples and evaluate for an infection in the urine. Urinalysis is done by collecting a clean catch, midstream urine in a sterile collection cup. The urine may be analyzed by the doctor in the office using or by analysis in a laboratory.

Because urine is normally sterile, any finding suggesting an infection may be considered abnormal and supportive of a kidney infection.

  • Gross inspection of urine (macroscopic analysis) may reveal cloudy urine.
  • With a dipstick urine test, typical findings consistent with urinary tract infection include positivity for leukocyte esterase, nitrates, or blood.
  • In microscopic urinalysis (analysis under the microscope), the presence of white blood cells, red blood cells, or bacteria in the urine is highly suggestive of a kidney infection. Generally, visualization of 100,000 bacteria in one cc of a urine sample supports the diagnosis of urinary tract infection or kidney infection.
  • In some situations, less than 100,000 bacteria may still be enough to make the diagnosis. If no white blood cells or bacteria are seen in the urine, then another diagnosis may need to be considered.
  • When bacteria are recovered from urine, they need to be further analyzed to determine the exact type of bacteria. Once the exact type of bacteria is known, usually its sensitivity to typical antibiotics is also tested to further guide treatment.
  • In more complicated kidney infections, imaging studies, such as a CT scan of the abdomen and pelvis, or an abdominal ultrasound, also may be necessary. Complicated kidney infections are usually associated with more severe symptoms and with the more significant involvement of the kidneys including an abscess or gas formation in the kidney which can be detected by CT scan or ultrasound.
  • Recurrent or long-standing (chronic) kidney infections sometimes result from kidney stones or other structural abnormalities, such as an enlarged prostate or long-standing reflux of urine in the ureters (vesicoureteral reflux). X-rays, ultrasounds, or CT scans may be necessary to investigate these cases.

Can You Treat Kidney Infections at Home with Remedies?

Home remedies will not cure kidney infections. However, home and natural remedies may help manage kidney infection symptoms like fever and nausea. Moreover, most kidney infections can be treated in a home setting with adequate oral hydration and antibiotics. 

What Antibiotics Are Used for the Treatment and Cure of Kidney Infections?

The most important component of the treatment of kidney infection is the prompt administration of antibiotics. As soon as the diagnosis of UTI or kidney infection is made by an analysis of urine, antibiotics need to be started. Typically, a strong antibiotic is started first, one which would be effective in treating all typical bacteria suspected of causing the infection. Once the actual bacteria are recovered and their sensitivity is determined, then a different antibiotic may be selected if the bacteria show resistance to the antibiotic that was originally started.

Several types of antibiotics are available and used to treat kidney infections. The choice depends on specific situations, clinical settings, tolerance, allergies, and ability to take oral medications.

Some of the common antibiotics used include

The doctor diagnosing the kidney infection can determine what is the most appropriate in a given situation. 

Similar to any infection, a routine follow-up with the physician treating the kidney infection is important to assure that therapy has been effective. More immediate follow-up may be necessary if the symptoms of the infection do not improve after a few days of antibiotics and supportive care. In such cases, further investigation may be necessary to rule out a complicated kidney infection and to assure that the organism causing the infection is sensitive to the prescribed antibiotics.

Are Kidney Infections Serious? What Is the Prognosis?

Generally, urinary tract and kidney infections are common conditions with an overall favorable outlook.

  • A kidney infection can be managed at home if the infection is diagnosed and treated early with antibiotics.
  • Severe or complicated infections may require more intensive treatment and possible hospitalization.
  • Personal hygiene is important in the prevention of recurring kidney infections.
  • Cranberry juice is a simple natural remedy to prevent recurring kidney infections.

Rarely, serious complications from a kidney infection may occur.

Can You Prevent Kidney Infections?

Prevention of urinary tract and kidney infections primarily focuses on reducing the associated risk factors. As mentioned earlier, the majority of urinary tract infections are caused by bacteria gaining entry into the urinary system through the urethra. Therefore, personal hygiene plays an important role in preventing kidney infections.

Examples of preventative measures include:

  • Emptying the bladder (urinating) after sexual intercourse or wiping it from front to back after going to the bathroom may significantly reduce the chance of developing kidney infection in women.
  • Drinking plenty of fluids (especially water) has been shown to be the single most effective measure for preventing urinary tract infections.
  • In individuals with long-standing urinary catheters, routinely scheduled changing of the catheter as well as regular cleaning around the catheter's entry into the urethra are important steps in the prevention of urinary tract infections.
  • If kidney stones are the predisposing factor to repeated kidney infections, the removal of the stone and preventing future stones from forming may be necessary. These individuals may be referred to a specialist (urologist) for further evaluation and removal of kidney stones.
  • Cranberries and cranberry juice can be beneficial in preventing kidney infections. It is important to note that cranberries may not treat an existing kidney infection, but have been found to be a simple preventive measure in addition to the other measures listed above.

Health Solutions From Our Sponsors

Urinary Tract Infection (UTI) Symptoms

Kidney infections often are caused by urinary tract infections (UTIs). Symptoms of a UTI include a sudden urge to urinate, pain or burning when urinating, and urine that is bloody, milky, with a foul odor. Contact your doctor if you think you may have a urinary tract infection.

Reviewed on 10/26/2022
Brusch, JL, MD, et al. Urinary Tract Infection (UTI) and Cystitis (Bladder Infection) in Females. Medscape. Updated: Jan 02, 2020.

Fulop, T, MD, et al. Acute Pyelonephritis. Medscape. Updated: Jun 14, 2019.