Specimen Collection for the diagnosis of Urinary Tract Infection

Both noninvasive and invasive methods for collecting urine are available. Sample obtained from invasive methods are reliable as they are less likely to be contaminated and easy to interpret but urine collected by noninvasive methods passes through the contaminated milieu, so quantitative cultures is used for the diagnosis of Urinary Tract Infections (UTI) and to discriminate between contamination, colonization and infection.

Commonly used methods for urine specimen collection:

  1. Suprapubic aspiration: Suprapubic aspiration is the best method to avoid contamination of specimens with bacteria in the distal urethra. Urine is withdrawn directly into a syringe through a percutaneously inserted needle.  This type of collection technique may be indicated in pediatric practice.
  2. Straight catheter technique: Collection of urine by use of a single catheter (straight catheter technique) is the next-best technique for obtaining urine specimens with minimal contamination
  3. Clean Catch Midstream Urine Collection: It is the least invasive technique and used widely. It has obvious disadvantage compared to techniques mentioned above. The chances of contamination from normal vaginal, perineal and anterior urethral flora  is high. Urine sample passes through the distal urethra and can become contaminated with commensal bacteria
  4. Indwelling Catheter: Specimen collection from patients with indwelling catheter requires scrupulous aseptic technique. The catheter tubing should be clamped off above the port to allow collection of freshly voided urine. The catheter port or wall of the tubing should then be cleaned vigorously with 70% ethanol, and urine aspirated via a needle or syringe; the integrity of the closed drainage system must be maintained to prevent the introduction of organisms in to the bladder.

Frequency of Use of Urine specimen collection Technique

  1. Clean-catch midstream technique: Most urine specimens are obtained from adult patients via the clean-catch midstream technique
  2. Suprapubic aspiration: Used infrequently because it is not indicated clinically (except in rare circumstances), it is invasive and uncomfortable, and it requires too much time and too many resources to be practical.
  3. Straight catheter technique: It is not indicated clinically for most patients because it is too labor intensive and costly for routine use. It is an invasive tehiques with  added disadvantages, because the process of inserting a catheter through the urethra can introduce bacteria into the bladder (and thereby cause UTI), and rare complications have been reported.