What is kidney infection?

Kidney infection is also known as pyelonephritis.  This disease occurs when the kidneys get infected which is usually due to a urinary tract infection (UTI) that has ascended from the urethra- a tube connecting the bladder to the opening of the genitalia for removal of urine.  This condition is usually caused by bacterial infections.  Kidney infection is a disease that requires immediate medical attention as it can damage the kidneys permanently and can even be life-threatening.

In the United States, kidney infection affects at least 250,000 people annually.  In addition, it is significantly more common in females than in males.

The management of kidney infection usually requires the use of antibiotics and often hospitalisation.

What are the risk factors for kidney infection?

There are several factors which may increase your risk of developing kidney infection and these include:

• Being female: Females are more at risk of developing kidney infection than men due to the fact that their urethra is shorter which facilitates the entry of bacteria into the bladder.  Furthermore, the anus is very close to the urethra in women which increases the risk of getting bacteria into the urethra.  Once the bacteria reaches the bladder, it can spread to the kidneys causing a kidney infection.  In addition, pregnant women are at highest risk of developing a kidney infection.

• Having a weakened immune system: Some medical conditions (diabetes or human immunodeficiency virus) or medications (corticosteroids) can weaken your immune system which may increase your risk of getting a kidney infection.
• Having a blockage in your urinary tract: Anything causing blockage within your urinary tract such as an enlarged prostate or kidney stone, will increase your risk of developing a kidney infection.
• Having a urinary catheter in place for a long period of time: A urinary catheter is a tube that is inserted into the urethra to reach the bladder to drain urine.  It can be used as a diagnostic test, during and after surgery.  In addition, urinary catheters are also used in people who are bedridden.

What are the signs and symptoms of kidney infection?

The signs and symptoms of kidney infection include:

• Fever (>39.4°C)
• Costovertebral pain: pain located on your back at the bottom of your ribcage.
• Nausea
• Vomiting
• Blood in urine (hematuria)
• Flank pain
• Frequent urination
• Pain or burning sensation when urinating
• Urine having a pungent smell
• Increased heart rate
• Pain below the umbilicus

Making a diagnosis

To make a diagnosis, your doctor will first take a detailed history from you to know more about your symptoms.  After the history taking, your doctor will perform a thorough physical examination to look for signs of pyelonephritis. 

For analysis of your urine, a clean-catch urine specimen will be required.  This is obtained by collecting urine midway during urination.  This is to avoid collection of contaminated urine at the start of urination. 

Urine samples may be obtained via urethral catheterisation also.  This is especially useful if:

• You cannot urinate properly
• The person is aged below 6 years
• You are bedridden
• You are obese
• You are too ill to perform a clean-catch procedure

The urine sample is examined under the microscope to look for white blood cells (WBCs) which will indicate the presence of infection.  In addition, red blood cells may also be identified which will indicate the presence of microscopic hematuria. 

Urine culture can be done to identify exactly which bacteria is causing the infection and which antibiotics will be most appropriate.  This is especially important due to the possibility of antibiotic resistance.

Imaging studies are warranted for people who has acquired immunodeficiency syndrome (AIDS), poorly controlled diabetes or a weakened immune system.  There are different imaging studies which can be performed and these include:

• Computed Tomography (CT) scan: CT scan is the imaging of choice as it can detect any abnormalities within the kidneys such as kidney stones, non-functioning of the kidneys, and thickening of the kidney wall amongst others.  This imaging technique is often done with the help of a contrast material for better imaging.

• Magnetic Resonance Imaging (MRI) scan: MRI scan can detect whether the kidney is functioning normally, masses or urinary obstruction.  As there is no radiation involved in this imaging technique, it can be used during pregnancy.
• Ultrasonography: This imaging technique is less accurate than CT or MRI scans but it can be used at bedside and is relatively inexpensive.  In addition, no radiation is involved and no contrast is required.

What are the treatment options of kidney infection?

Antibiotics are the drugs of choice for the management of pyelonephritis.  The choice of antibiotics to be used will depend on which bacteria is causing the infection.  Your signs and symptoms usually start to improve after a few days following antibiotics use.  However, it is of utmost importance to complete the full course of the antibiotic in order to avoid antibiotic resistance.  After the antibiotic treatment, your doctor may repeat a urine culture to determine whether the infection has been cleared or not.  In very severe cases, hospitalisation may be required to provide the antibiotics through your veins which will increase your rate of recovery.

What are the complications of kidney infection?

If kidney infection is left untreated, the following complications may ensue:

• Scarring of your kidney tissue: This can result in high blood pressure, chronic kidney disease and even kidney failure.

• Septicaemia: This condition is also known as blood poisoning which occurs when the infection spreads to your blood which may be life-threatening.
• Delivering low weight babies: Pregnant women suffering from pyelonephritis have an increased risk of delivering low weight babies.

Prognosis

Diagnosing pyelonephritis early is of utmost importance as it has a significant impact on the prognosis.  Sudden deterioration of health in someone with pyelonephritis indicates the presence of a complication or a resistant bacteria which will require prompt medical intervention.  Follow up of the disease is very important to make sure that the disease progression is satisfactory and that recovery is complete.  People suffering from pyelonephritis along with diabetes are significantly more prone to complications and have longer hospital stays.

J. Alastair, I. and Simon, M., 2016. Davidson's Essentials of Medicine. 2nd ed. London: ELSEVIER.

Parveen, K. and Michael, C., 2017. Kumar & Clarks Clinical Medicine. 9th ed. The Netherlands: ELSEVIER.

Fulop, T., 2020. Acute Pyelonephritis Workup.

Fulop, T., 2020. Acute Pyelonephritis Treatment & Management.