Editing Urinary Tract Infections (section)

=== Labs ===

==== Urine collection ====
* '''Voided and catheterized specimens'''
** '''Males'''
*** '''In circumcised males, voided specimens require no preparation. For males who are not circumcised, the foreskin should be retracted and the glans penis washed with soap and then rinsed with water before specimen collection.'''
*** '''The first 10 mL of urine (representative of the urethra) and a midstream specimen (representative of the bladder) should be obtained.'''
*** '''Prostatic fluid is obtained by performing digital prostatic massage''' and collecting the expressed prostatic fluid on a glass slide. In addition, '''collection of the first 10 mL of voided urine after massage will reflect the prostatic fluid added to the urethral specimen.'''
*** Catheterization of a male patient for urine culture is not indicated unless the patient cannot urinate.
** '''Females'''
*** '''In females, contamination of a midstream urine specimen with introital bacteria and WBCs is common, particularly when the woman has difficulty spreading and maintaining separation of the labia. Therefore, females should be instructed to spread the labia, wash and cleanse the periurethral area with moist gauze, and then collect a midstream urine specimen.'''
**** '''Cleansing with antiseptics is not recommended''' because they may contaminate the voided specimen and provide a false-negative urine culture.
*** '''The voided specimen is contaminated if it shows evidence of vaginal epithelial cells and lactobacilli on urinalysis,''' and a catheterized specimen should be collected.
* '''Suprapubic aspiration'''
** '''Advantage: highly accurate'''
** '''Disadvantages:''' '''some morbidity'''
** '''Limited clinical usefulness''' except for a patient who cannot urinate on command such as patients with spinal cord injuries and newborns
** Steps to perform procedure available in CW11 page 250
* '''Bag specimens'''
** '''Unreliable and unacceptable for diagnosis of UTI in high-risk populations and infants'''.
*** '''Generally, if a UTI is suspected in a child who is not yet toilet trained, only a catheterized or needle-aspirated specimen is acceptable for diagnosis''' because bagged urinary specimens have an unacceptably high false-positive rate.
**** Under special collection circumstances when the perineum is cleaned well and the bag removed and processed promptly after voiding, a bagged specimen or even a diaper specimen that shows no growth is useful in eliminating bacteriuria as a diagnosis.

==== Urinalysis (UA) ====
* '''Provides rapid identification of bacteria and WBCs and presumptive diagnosis of UTI'''
** '''Assess for bacteria, epithelial cells, pyuria, hematuria, nitrites'''
** '''Diagnosis is confirmed by urine culture'''
*** UA does not replace urine culture and may be more relevant for screening in asymptomatic patients
* Usually, the sediment from an ≈5-10-mL specimen obtained by centrifugation for 5 minutes at 2000 rpm is analyzed.
* '''Bacteriuria'''
** Definition of bacteriuria: presence of bacteria in the urine, which is normally free of bacteria
*** The term "significant bacteriuria" has a clinical connotation and is used to describe the number of bacteria in a suprapubically aspirated, catheterized, or voided specimen that exceeds the number usually caused by bacterial contamination of the skin, the urethra, or the prepuce or introitus, respectively.
** '''Can be symptomatic or asymptomatic'''
** '''Found in > 90% of infections with counts of ≥105 colony-forming units (cfu) per milliliter of urine and''' '''is a highly specific finding'''.
*** Bacteria are usually not detectable microscopically with lower cfu (102-104/mL).
** '''Causes of false-negative UA and culture:'''
**# '''Early in an infection'''
**# '''In context of increased fluid intake and subsequent dilute urine'''
*** '''A negative urinalysis for bacteria never excludes the presence of bacteria'''
** '''Causes of false-positive UA and culture:'''
**# '''Contamination of an abacteriuric specimen during collection'''
**#* '''Contamination can be considered if numerous squamous epithelial cells''' (indicative of preputial, vaginal, or urethral contaminants) '''are present'''
**#** The possibility of contamination increases as the reliability of the collection technique decreases from suprapubic aspiration to catheterization to voided specimens
* '''Pyuria'''
** '''Definition of pyuria:''' presence of white blood cells in the urine, '''generally indicative of infection and/or an inflammatory response''' of the urothelium to the bacterium, stones, or other indwelling foreign body.
** '''The absence of pyuria should cause the diagnosis of UTI to be questioned until urine culture results are available.'''
** '''Bacteriuria without pyuria is generally indicative of bacterial colonization without infection of the urinary tract.'''
** '''Sterile pyuria (pyruria without bacteriuria) warrants evaluation for tuberculosis, stones, or cancer. Many other causes§'''
*** '''Almost any injury to the urinary tract''', from chlamydial urethritis to glomerulonephritis and interstitial cystitis, '''can elicit large numbers of fresh polymorphonuclear leukocytes'''
** '''Tests for detecting pyuria by determining leukocyte esterase activity have been developed'''
* '''Nitrites'''
** '''Bacteria may convert urinary nitrates into nitrites and this may be used as evidence of UTI.'''
*** '''Gram-negative bacteria of the Enterobacteriaceae family (Escherichia coli, Klebsiella, Proteus, Enterobacter, Serratia, or Citrobacter) commonly convert nitrates to nitrites, while Gram-positive species (enterococcus, staphylococcus) generally do not.'''
**** '''One very important gram-negative exception is Pseudomonas, which does not contain the enzymatic machinery to convert nitrates to nitrites'''
* Hematuria
** Indicator of an inflammatory response
** Microscopic hematuria is found in 40-60% of cases of cystitis and is uncommon in other dysuric syndromes

==== Urine culture ====
* Techniques available (2): direct surface plating and dip slides
* '''Urine must be refrigerated immediately on collection and should be cultured within 24 hours of refrigeration.'''
* '''A cut-off of ≥105/mL has been proposed to define significant bacteruria [from a midstream specimen]'''
** '''However, 20-40% of women with symptomatic UTIs present with bacteria counts of 102-104 cfu/mL of urine; therefore, in dysuric patients, an appropriate threshold value for defining significant bacteriuria is 102 cfu/mL of a known pathogen.'''
** The ≥105 cut-off may also lead to overdiagnosis in patients with contaminated urine.

==== Localization ====
* Kidney
** Fever and flank pain are common in pyelonephritis, but can also occur in infections localized to the bladder
** Ureteral catherization allows separation of bacterial persistence into upper and lower urinary tracts and also separation of laterality of kidney infection.