Editing Urinary Tract Infections (section)

==== 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