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UTI Uncomplicated vs. UTI Complicated

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Author:    Pamela Downey (MSN, ARNP)


Urinary tract infections (UTIs) start with the colonization of uropathogens in the vaginal introitus or the urethral meatus. The colonization then moves up through the urethra into the bladder. This infection of the bladder and lower urinary tract is called cystitis. When an infection ascends into the upper urinary tract and the kidneys, it is called pyelonephritis. A UTI that extends beyond the bladder and includes a fever or other systemic symptoms is a complicated UTI. Complicated UTIs can lead to sepsis.


UTIs can be clinically categorized as either acute uncomplicated UTIs or acute complicated UTIs based on the extent and severity of the infection. This categorization directs the management of care and differs from other conventions.

Let’s compare:

Acute Uncomplicated UTIs

Acute uncomplicated UTIs typically affect individuals, especially women, children, and elderly individuals who are otherwise healthy and have no structural or neurological urinary tract abnormalities.

An acute uncomplicated UTI is presumed to be confined to the bladder (cystitis), i.e., lower UTI with no signs or symptoms that suggest an upper tract or systemic infection.

Risk factors associated with cystitis include (Hooton & Gupta, 2021; Flores-Mireles et al., 2015):

  • Diabetes
  • Female gender
  • Genetic susceptibility
  • Obesity
  • Prior history of a UTI
  • Sexual activity
  • Vaginal infection

Nonpregnant, premenopausal women who do not have a urologic abnormality are considered uncomplicated even with cystitis or pyelonephritis (Hooton & Gupta, 2021).

Acute Complicated UTIs

Acute complicated UTI has been defined as upper UTIs (pyelonephritis) associated with factors that compromise the urinary tract or host defense (Hooton & Gupta, 2021).

The term "acute complicated UTI" refers to an acute UTI with any of the following features, which suggest that the infection extends beyond the bladder (Hooton & Gupta, 2021):

  • CVA tenderness
  • Fever (>99.9°F/37.7°C)
    • This temperature threshold is not well defined and should be individualized, considering:
      • Baseline temperature
      • Other potential contributors to an elevated temperature
      • The risk of poor outcomes should empiric antimicrobial therapy be inappropriate
  • Flank pain
  • Other signs or symptoms of a systemic illness include:
    • Chills or rigors
    • Significant fatigue or malaise beyond the baseline
    • Pelvic or perineal pain in men can suggest accompanying prostatitis

By this above definition, pyelonephritis is an acute complicated UTI, regardless of patient characteristics. In the absence of any of the above symptoms, patients with a UTI should be considered to have acute simple cystitis, and thus the patient is managed differently. 

Risk factors associated with acute complicated UTIs include (Hooton & Gupta, 2021):

  • Exposure to antibiotics
  • Immunosuppression
  • Pregnancy
  • Presence of foreign bodies such as calculi, indwelling catheters, or other drainage devices
  • Renal failure
  • Renal transplantation
  • Urinary obstruction
  • Urinary tract abnormalities
  • Urinary retention caused by neurological disease

In the U.S., 70 to 80% of acute complicated UTIs are attributable to indwelling catheters, accounting for one million cases/year.

Catheter-associated UTIs (CAUTIs) increases morbidity and mortality and are the most common cause of sepsis. Risk factors for developing a CAUTI include (Hooton & Gupta, 2021):

  • Diabetes
  • Female gender
  • Older age
  • Prolonged catheterization

Genitourinary Abnormalities

Genitourinary abnormalities may be associated with an acute complicated UTI (See Table 1). Blockage to a normal stream of urine decreases the flushing action of bacteria. Mechanisms of infection include (Hooton & Gupta, 2021):

  • Genitourinary tract instrumentation increasing introduction of organisms
  • Obstruction with incomplete urinary drainage
  • Persistence of bacteria in biofilm on stones or indwelling devices 

The risk of infection varies with different abnormalities. 

Table 1
Structural and Functional Abnormalities of the Genitourinary Tract Associated with an Acute Complicated UTI
  • Congenital abnormalities
  • Diverticulae
  • Pelvicalyceal obstruction
  • Prostatic hypertrophy
  • Renal cysts
  • Tumors of the urinary tract
  • Ureteric or urethral strictures
  • Urolithiasis
  • Indwelling urethral catheter
  • Intermittent catheterization
  • Nephrostomy tube
  • Ureteric stent
  • Urological procedures
Impaired voiding
  • Neurogenic bladder
  • Cystocele
  • Vesicoureteral reflux
  • Ileal conduit
Metabolic abnormalities
  • Nephrocalcinosis
  • Medullary sponge kidney
  • Renal failure
  • Renal transplant

Specific Patient Populations

An acute complicated UTI occurs in people of any age group (Hooton & Gupta, 2021):

  • Men are not generally considered to have acute complicated UTI without concerning symptoms. However, the possibility of prostatic involvement should always be considered. Because uncomplicated UTI is rare in men, any male urinary infection is usually considered to be complicated.
  • Increased residual urine volume, cystoceles, and a history of genitourinary surgery associated often times with postmenopausal women are issues consistent with a complicated infection.
  • Cystitis or pyelonephritis in a nonpregnant, premenopausal woman without risk factors is considered an acute uncomplicated UTI.

Signs and Symptoms

The typical presentation of UTI encompasses both cystitis with complicating features and pyelonephritis.

Signs and symptoms of cystitis include (Hooton & Gupta, 2021; McLellan & Hunstad, 2017):

  • Dysuria
  • Urinary frequency
  • Urinary urgency
  • Suprapubic pain
  • Hematuria

Signs and symptoms of acute complicated UTI which suggest that infection has extended beyond the bladder include (Hooton & Gupta, 2021; McLellan & Hunstad, 2017):

  • Fever
  • Other features of systemic illness such as:
    • Chills
    • Marked fatigue or malaise beyond the baseline
    • Rigors

Signs and symptoms of pyelonephritis classically include (Hooton & Gupta, 2021; McLellan & Hunstad, 2017):

  • Fever/chills/rigors
  • Flank pain
  • CVA tenderness
  • Nausea/vomiting
  • Symptoms of cystitis are often but not always present
  • Atypical symptoms may occur, including:
    • Pain in the epigastrium
    • Pain in the lower abdomen
  • For men, the presentation of recurrent UTI with pelvic or perineal pain can include prostatitis

Not all patients with acute complicated UTI present with clear symptoms localized to the urinary tract. For example (Hooton & Gupta, 2021; McLellan & Hunstad, 2017):

  • Patients with neurological illnesses may have atypical presentations:
    • Spinal cord injuries and neurogenic bladder patients may have autonomic dysreflexia and increased bladder and leg spasms.
    • Patients with multiple sclerosis may have deterioration in neurological function and increased fatigue.
  • Elderly or debilitated patients may present with more generalized signs or symptoms of infection without clear symptoms of UTI.
    • Patients and caregivers often interpret cloudy or foul-smelling urine as a UTI. This finding may accompany bacteriuria; it is not diagnostic.
  • Patients with chronic symptoms or impaired communication are more problematic.
  • For patients with indwelling catheters, clinical deterioration without genitourinary symptoms is seldom due to UTI.
    • Fever without genitourinary symptoms is a common presentation of UTI in patients with indwelling catheters.


Patients with acute complicated UTI may be associated with severe morbidities, such as septic shock or death. However, patients may also present with (Hooton & Gupta, 2021):

  • Acute renal failure
    • Acute renal failure is more likely to occur in patients with:
      • Diabetes mellitus
      • Increased age
      • Recent urinary tract instrumentation
      • Urinary tract abnormalities
      • Urinary tract obstruction(s)
    • When renal failure occurs in patients with an acute complicated UTI, deterioration in renal function is usually caused by the underlying urological defect rather than infection.
  • Bacteremia
  • Multiple organ system dysfunctions
  • Sepsis
  • Shock
  • Acute or chronic infection is occasionally associated with suppurative complications, such as:
    • Metastatic infection, including bone and joint infection or endocarditis
    • Paraurethral abscesses
    • Renal abscesses
    • Perirenal abscess

Acute pyelonephritis can also be complicated (Hooton & Gupta, 2021):

  • Emphysematous pyelonephritis
  • Papillary necrosis
  • Perinephric abscess
  • Progression of the upper urinary tract infection to renal corticomedullary abscess 

Massive destruction of the kidney by granulomatous tissue, usually due to obstruction by renal stones, is xanthogranulomatous (Hooton & Gupta, 2021). Nonspecific signs and symptoms like malaise, fatigue, nausea, or abdominal pain may persist for weeks or months before presentation.


It is important to be able to differentiate uncomplicated from complicated UTIs. Remember to always consider the atypical presentations as well.

Implicit Bias Statement

CEUFast, Inc. is committed to furthering diversity, equity, and inclusion (DEI). While reflecting on this course content, CEUFast, Inc. would like you to consider your individual perspective and question your own biases. Remember, implicit bias is a form of bias that impacts our practice as healthcare professionals. Implicit bias occurs when we have automatic prejudices, judgments, and/or a general attitude towards a person or a group of people based on associated stereotypes we have formed over time. These automatic thoughts occur without our conscious knowledge and without our intentional desire to discriminate. The concern with implicit bias is that this can impact our actions and decisions with our workplace leadership, colleagues, and even our patients. While it is our universal goal to treat everyone equally, our implicit biases can influence our interactions, assessments, communication, prioritization, and decision-making concerning patients, which can ultimately adversely impact health outcomes. It is important to keep this in mind in order to intentionally work to self-identify our own risk areas where our implicit biases might influence our behaviors. Together, we can cease perpetuating stereotypes and remind each other to remain mindful to help avoid reacting according to biases that are contrary to our conscious beliefs and values.


  • Flores-Mireles, A., Walker, J., Caparon, M., & Hultgren, S. (2015). Urinary tract infections: Epidemiology, mechanisms of infection, and treatment options. Nature Reviews Microbiology. 13 (5): 269-284. Visit Source.
  • Hooton, T., & Gupta, K. (2021). Acute complicated urinary tract infection (including pyelonephritis) in adults. UpToDate. Visit Source.
  • McLellan, L., & Hunstad, D. (2017) Urinary tract infection: Pathogenesis and outlook. Trends in Molecular Medicine. 22 (11): 946-957. Visit Source.