Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (247 page)

   Renal tissues may be infected by ascending infection through the ureters or by hematogenous seeding during bacteremia.

   
Asymptomatic bacteriuria
is defined by a urine culture, submitted by a patient without dysuria or other symptoms of UTI, that yields growth of >10
⁵
cfu/mL of a single uropathogen. Pregnant women with asymptomatic bacteriuria are at increased risk for developing UTI, including pyelonephritis, and low birth weight infants. Screening for asymptomatic bacteriuria with a routine urine culture at 12–16 weeks of gestation is recommended. Antibiotic treatment significantly reduces the risks associated with asymptomatic bacteriuria in pregnant women. The clinical value of treating asymptomatic bacteriuria in men or in nonpregnant women has not been established. Screening for asymptomatic bacteriuria in these groups is not recommended.

   
Renal abscess
: Most renal abscesses occur in the setting of obstructive pyelonephritis, caused by ascending infection. Predisposing factors include diabetes, renal stones, tumor, neurogenic bladder, and vesicoureteral reflux. Enteric bacilli are implicated most frequently, but polymicrobial infections occur commonly. Renal abscess and perinephric abscess may also occur as a result of hematologic seeding of the renal parenchyma or perirenal fat and are usually caused by
S. aureus
. Signs and symptoms of renal or perinephric abscess are similar to those of severe pyelonephritis.

   
Sterile pyuria
: Conditions other than acute bacterial UTI should be considered for patients with pyuria (≥10 WBC/HPF) and negative urine culture. Potential causes include infectious conditions (e.g., renal tuberculosis, urethritis/STI, prostatitis, and viral cystitis or genital infection) and noninfectious conditions (e.g., inflammation by exposure to allergen or chemical agent, mechanical irritation due to stone or instrumentation, renal diseases associated with inflammation).

   Who Should Be Suspected/Who Should Be Tested?

   Risk factors for complicated UTI:

   
Pregnancy

   
Urinary tract abnormality
, including anatomical obstruction, indwelling foreign body, recent surgery, or instrumentation

   
Medical conditions
, including diabetes, underlying renal disease, immunosuppression, history of complicated UTI, or recent hospitalization

   Clinical signs and symptoms

   
Cystitis
: Dysuria, urgency, frequency, suprapubic pain, hematuria.

   
Pyelonephritis
: Fever (>38°C), flank pain, costovertebral angle tenderness, nausea, vomiting, malaise. Signs and symptoms of cystitis are common. Patients may present with signs of sepsis and multiple organ failure.