When to Go to the Hospital for a Kidney Infection
Medically reviewed by Michael Menna, DO
There are times when the symptoms of a kidney infection can turn severe. Knowing the signs and when to go to the hospital can help you avoid potentially life-threatening complications like kidney failure and sepsis.
A kidney infection (also known as pyelonephritis) is a type of urinary tract infection (UTI) that typically starts in the tube that carries urine from the body (urethra) or the bladder. While many cases can be treated at home with oral antibiotics, hospitalization may be needed for especially severe cases.
This article explains how kidney infections occur, including the causes and symptoms. It also describes the signs of a severe kidney infection and what to expect if hospitalization is needed.
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A Note on Gender and Sex Terminology
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Sex refers to biology: chromosomal makeup, hormones, and anatomy. People are most often assigned male or female at birth based on their external anatomy; some people do not fit into that sex binary and are intersex.
Gender describes a person's internal sense of self as a woman, man, nonbinary person, or another gender, and the associated social and cultural ideas about roles, behaviors, expressions, and characteristics.
Research studies sometimes don't use the terminology in this way. Terms that describe gender (“woman,” “man”) may be used when terms for sex (“female,” “male”) are more appropriate. To reflect our sources accurately, this article uses terms like "female," "male," "woman," and "man" as the sources use them.
How Does a Kidney Infection Start?
A kidney infection is typically caused by bacteria. Around 90% are due to bacteria called Escherichia coli (E. coli), but others like Enterococcus faecalis, Pseudomonas aeruginosa, and Klebsiella pneumoniae can also cause an infection.
Most cases start off as a lower urinary tract infection that migrates up the urethra to the bladder. Thereafter, the infection can spread to one or both kidneys through tubes that connect the bladder to the kidneys, called ureters.
On rare occasions, a kidney infection can occur after kidney surgery or when an infection from another surgery (such as a heart valve or artificial joint replacement) spreads to the kidneys.
Kidney infections affect females more than males due to their urethras being shorter and situated close to the anus. Fluctuations in the hormone estrogen—which helps maintain the integrity of vaginal and urinary tract tissues—can also increase the risk of infection during menstruation, pregnancy, and menopause.
Several other factors can significantly increase your risk of a kidney infection, including:
Urinary tract obstruction: This includes having a kidney or bladder stone, enlarged prostate, bladder outlet obstruction, or urethral stricture (a narrowing of the urethra).
Urinary catheters: The prolonged use of catheters increases the risk of bacterial infection.
Vesicoureteral reflux: This is a condition in which urine flows backward (refluxes) from the bladder to the kidneys.
Having a weakened immune system: People with untreated human immunodeficiency virus (HIV), organ transplant recipients, or people on immunosuppressant drugs have a harder time fighting infections.
Having diabetes: High blood sugar damages tissues of the urinary tract and provides "fuel" for bacteria to grow on.
Neurogenic bladder: This is the nerve-related dysfunction of the bladder often seen in people with multiple sclerosis, stroke, spina bifida, or spinal cord trauma.
Related: Causes of Kidney Pain You Should Know
What Does a Kidney Infection Feel Like?
A kidney infection can either be acute (sudden and severe) or chronic (persistent or recurrent). Both can cause serious complications if left untreated.
Acute pyelonephritis typically develops quickly over the course of a few hours or a day, causing symptoms like:
High fever
Flank pain (affecting the sides of the abdomen between the lower ribs and hips)
Nausea and vomiting
Chronic pyelonephritis is often caused by ongoing conditions like vesicoureteral reflux, causing symptoms like:
Persistent low-grade fever
Persistent flank pain
Chronic fatigue
Unintentional weight loss
Related: Kidney Infection: Signs, Symptoms, and Complications
How Severe Is a Kidney Infection?
Acute pyelonephritis is designated as either uncomplicated or complicated. Uncomplicated kidney infections can usually be treated at home, while complicated cases may require inpatient care in a hospital.
Complicated acute pyelonephritis most often affects vulnerable people, including immunocompromised people, pregnant people, and people with uncontrolled diabetes, kidney transplants, urinary tract abnormalities, and hospital-acquired bacterial infections.
Complications of acute pyelonephritis include:
Renal abscess: A pocket of pus (abscess) in kidney tissues
Pyonephrosis: A serious infection that causes the buildup of pus in the center of a kidney, causing it to swell
Renal vein thrombosis: A rare condition in which a blood clot (thrombus) forms in the renal vein that transports blood from the kidneys to the heart
Papillary necrosis: The death (necrosis) of the tiny tubules inside the kidneys that direct urine to the ureters
Acute renal failure: The abrupt and potentially life-threatening loss of kidney function
Emphysematous pyelonephritis: A potentially life-threatening infection that causes the death of the functional structures of the kidneys
Sepsis: A potentially life-threatening condition in which the body triggers a massive inflammatory response to an infection that has spread into the bloodstream
When to Make an Office Appointment
Any time you have symptoms of a urinary tract infection, contact a healthcare provider. They will likely order a urine test and schedule an office visit or direct you to an urgent care clinic.
Common symptoms of a UTI include:
Feeling pain or burning when urinating
Having the urge to urinate frequently
Foul-smelling urine
Cloudy or red urine
Feeling pressure or cramping in the lower abdomen or back
Low-grade fever (not always present)
When to Go to the Hospital
Although many lower UTIs will clear on their own, upper UTIs like pyelonephritis are less likely to do so and may turn serious quickly.
Given that acute pyelonephritis develops rapidly, it is important to seek immediate care if you develop symptoms. If your healthcare provider is unavailable, go to your nearest urgent care center. When treated early, most kidney infections can be cleared with a short course of antibiotics.
In other instances, you will need to call 911 or go to the emergency room—especially if there are signs of acute renal failure or sepsis. If left untreated, sepsis can lead to septic shock, causing organ failure and death, sometimes within 12 hours.
Signs of a medical emergency include:
High fever with shaking chills
Severe flank and back pain
Abdominal pain with swelling
Vomiting
Low urine output or inability to urinate
Light-headedness or fainting
Do You Have to Be Hospitalized to Treat a Kidney Infection?
Certain people with pyelonephritis may need to be hospitalized even if their symptoms do not seem critical. This is because the risk of complications is high.
Hospitalization may be needed if you have a severe kidney infection and you:
Are an older adult
Are pregnant and have a fever or other illness
Have kidney stones or a urinary tract abnormality
Recently had urinary tract surgery
Have cancer, uncontrolled diabetes, neurogenic bladder, or other medical concerns
Failed antibiotic treatment at home
Acute Pyelonephritis and Pregnancy
Pyelonephritis affects approximately 2% of all pregnancies in the United States, with 80% to 90% of cases occurring during the second and third trimesters. It is associated with a high risk of complications (including maternal sepsis and preterm birth) as well as an increased risk of maternal and fetal death.
How Is a Kidney Infection Diagnosed?
A kidney infection is mainly diagnosed with urine tests and imaging studies. The results of the tests will help direct the appropriate treatment.
These include:
Urinalysis: This is a chemical and microscopic evaluation of a urine sample to check signs of infection, including bacteria and defensive white blood cells.
Urine culture: This is a lab procedure that grows bacteria from a sample of urine to determine the bacterial cause of your infection.
Antimicrobial susceptibility testing: Bacteria identified by a urine culture are tested for their response to different antibiotics.
Ultrasound: This is a noninvasive imaging tool that can visualize the size and structure of the kidneys using reflected sound waves.
Computed tomography (CT): This is an imaging technology that composites multiple X-ray images to create three-dimensional (3D) views of internal organs.
Magnetic resonance imaging (MRI): This imaging technology uses powerful magnetic and radio waves to create highly detailed images of soft tissues.
Differential Diagnosis
As part of the diagnosis, your healthcare provider may want to exclude other conditions that mimic the signs of a kidney infection. This helps ensure the correct treatment is given.
Among the conditions commonly included in the differential diagnosis are:
Appendicitis: Inflammation of the appendix
Cystitis: Bladder infection
Endometriosis: Growth of tissues similar to the uterine lining outside of the uterus
Pelvic inflammatory disease (PID): A chronic inflammatory condition affecting the uterus, ovaries, and fallopian tubes
Pregnancy: Often characterized by flank pain and urinary symptoms
Prostatitis: Inflammation of the prostate gland
What Is the Treatment for Kidney Infection Like?
For uncomplicated pyelonephritis, the standard treatment is a short course of oral antibiotics taken by mouth. The American College of Physicians recommends either a fluoroquinolone antibiotic like Levaquin (levofloxacin) or Cipro (ciprofloxacin) for five to seven days or Bactrim (trimethoprim-sulfamethoxazole) for 10 to 14 days.
When hospitalization is needed, the treatment is more often intravenous (IV; delivered into a vein). This is because:
IV antibiotics allow the drugs to enter the bloodstream directly and bypass absorption in the gut. This means that higher concentrations can reach tissues faster.
IV fluids quickly lower acid levels in the blood caused by infection. They also help replenish fluids in people who cannot take fluids by mouth.
In some cases, IV antibiotics are combined with oral antibiotics.
The choice of IV antibiotic depends on how severe the infection is and whether the bacteria are resistant to a group of antibiotics known as beta-lactams (which include penicillins).
The antibiotics are given by slow infusion anywhere from one to four times daily and dosed in grams (g), milligrams (mg), or milligrams per kilogram of body weight (mg/kg).
The standard duration of therapy is seven to 14 days.
Mild to Moderate Infection
Maxipime (cefepime) 1–2 g once daily
Rocephin (ceftriaxone) 1 g once daily
Cipro (ciprofloxacin) 400 mg every 12 hours
Garamycin (gentamicin) 5 mg/kg once daily
Levaquin (levofloxacin), 750 mg once daily
Zosyn (piperacillin + tazobactam) 3.375–4.5 g every 6 hours
Severe or Beta-Lactam Resistance
Avycaz (ceftazidime + avibactam) 2.5 g every 8 hours
Invanz (ertapenem) 1 g once daily
Merrem (meropenem) 1 g every 8 hours
Primaxin (imipenem +cilastatin) 500 mg every 6 hours
Vabomere (meropenem + vaborbactam
Zemdri (plazomicin) 15 mg/kg once daily
Zerbaxa (ceftolozane +tazobactam) 1.5 g every 8 hours
Related: How a Kidney Infection Is Treated
What Is My Outlook After a Kidney Infection?
The prognosis for a kidney infection is generally good if the appropriate treatment is delivered in a timely manner. This is true even if a person develops acute kidney failure, the condition of which is usually reversible.
The same cannot be said if treatment is delayed. In some cases, a kidney infection can severely damage the kidneys, leading to lifelong chronic kidney disease (CKD).
With emphysemic pyelonephritis (one of the most severe complications of acute pyelonephritis). the risk of death is high if left untreated. If treated appropriately, nearly 9 out of 10 people recover, albeit with some level of kidney dysfunction.
For people with complicated acute pyelonephritis, the risk of death from sepsis and septic shock is as high as 17.7% (or roughly 1 out of 6 people).
Summary
Uncomplicated kidney infections (acute pyelonephritis) are most often caused by the bacteria E. coli and treated at home with a five- to 14-day course of oral antibiotics. Other bacteria can also cause kidney infections, some of which are more difficult to treat.
Complicated acute pyelonephritis may require hospitalization, particularly in older people, immunocompromised people, pregnant people, or those with medical conditions like diabetes, multiple sclerosis, or cancer.
Unlike ordinary urinary tract infections (UTIs), kidney infections rarely resolve on their own. For hospitalized people, the treatment usually involves IV fluids and antibiotics. The choice of antibiotics varies based on the severity of the infection and the absence or presence of antibiotic-resistant bacteria.
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