Pathology of Urinary Tract Infection Flashcards
What is the presentation of a UTI?
Dysuria
Frequent urination
Smelly urine
In very young - generally unwell, failure to thrive
In very old - incontinence, immobility
What percentage of cardiac output does renal blood flow receive?
20-25%
In the normal renal tract, urine output changes with what?
Oral intake of fluids
Resorption of fluid is diminished if there is an increase in fluid intake and urine output will be increased
How does urine move through the ureters?
The movement of urine is continuous, the ureters do not store urine
What stops the reflux of urine?
The ureters enter the bladder at an angle, so as the bladder fills there is increasing pressure which closes off the ureter and stops the reflux of urine
What are the normal properties of urine?
Low pH
High osmolality
High ammonia
Prostatic secretions are
bacteriostatic
What parts of the urinary tract are sterile?
All of the urinary tract except for the terminal urethra
Subrapubic aspirate of urine will also be sterile
What is the main difference between a urinated sample of urine, compared to one obtained by a catheter?
A urinated sample will always be contaminated by the terminal urethral flora
What can be taken to obtain a sterile sample of urine?
A suprapubic aspirate of urine from the bladder
What process will flush out many of the terminal urethral floral bacteria?
Initial voiding - so initial urine will be heavily contaminated
When should urine specimens be collected?
After the initial void - ask the patient to void, stop mid-stream (discarding any collected urine), and then collect the next volume of urine - mid stream specimen of urine (MSSU)
Why is there no such thing as a negative MSSU?
The urethral flora is diminished by always present, so will always grow in a culture
What is the quick method for MSSU?
Dip slide method
When does an MSSU culture usually indicate an infection?
10^3 - 10^4 bacteria per ml sometimes indicates an infection
10^3 - 10^4 probable infection if symptomatic, 50% chance of infection if asymptomatic
If < 10^3 usually no infection
10^5 per ml represents infection
In what patients is an MSSU difficult to obtain?
In young children and the elderly
What are the usual causative organisms of UTI?
Gut flora, particularly E. coli
Viral infection rare
What is the normal route of infection of a UTI?
Almost always ascending i.e. from the terminal urethra to the bladder
Infection in the kidneys has usually spread from a bladder infection, upper UTIs more serious than lower
What are the names for infections of the;
- urethra
- bladder
- ureter
- kidney
Urethra - urethritis
Bladder - cystitis
Ureter - ureteritis
Kidney - acute or chronic pyelonephritis
What are the predisposing factors to a UTI?
Stasis of urine
Pushing bacteria up the urethra from below
Generalised predisposition to infection
What is the cause of stasis of urine?
Obstruction - congenital or acquired
Loss of feeling of full bladder e.g. spinal cord/brain injury
How does stasis of urine at the level of the urethra lead to UTI?
Bacteria that get higher up do not get flushed out
Upper urethral and bladder dilatation
-> Bilateral hydroureter (dilatation)
Or vice versa
Leads to bilateral hydronephrosis -> chronic renal failure
How does stasis of urine at the level of the renal pelvis on one side lead to UTI?
Unilateral hydroureter
-> unilateral hydroureter and unilateral hydronephrosis
What are the consequences of obstruction?
Proximal dilatation
Slowed urine flow -> can’t flush out bacteria -> infection
Slowed urine flow -> sediments form -> calculous formation -> obstruction
Obstruction from calculous -> more dilatation, more calculous formation, more infection
Triad - infection, calculi, obstruction
