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Culture, Urine, Routine

Test code(s) 395

Question 1. What is the best way to collect specimens from indwelling catheters?

  1. Disinfect the catheter port with 70% alcohol and allow it to dry.
  2. Aspirate at least 5-10 mL of urine using a sterile needle and syringe.
  3. Transfer the urine to a urine transport tube (Vacutainer® grey-top tube). This transport tube already contains a preservative that prevents rapid multiplication of bacteria during specimen transport. Bacterial multiplication could cause the colony count to be erroneously high. Stability is 48 hours at room temperature or refrigerated.

Note: Specimens collected from the collection bag are not suitable for analysis. Please go to this link for more information: http://questdiagnostics.com/directoryofservices/index.html page 114-115.

Question 2. How should small volume (<4 mL) urine specimens be collected?

When submitting less than 4 mL of urine, place the urine in a sterile container and ship refrigerated. DO NOT put less than 4 mL in a Vacutainer® grey-top tube.

Note: Do not send more than 5 mL of nonrefrigerated urine in a sterile container. Such specimens are unacceptable for routine bacterial culture.

Question 3. What is the minimum time recommended for incubating urine cultures?

A minimum of 16 hours of incubation is recommended before examination of culture media. Cultures can be reported as no growth after 18 hours of incubation.1

Question 4. A urine specimen was reported as having a high white blood cell count (5 to 8 WBC per high power field) but no growth during culture. How is that possible?

An injury in the urinary tract can account for such findings, which are referred to as sterile pyuria. Sterile pyuria is more common in catheterized patients and in patients with:

  • Vesicourethral reflex
  • Interstitial cystitis
  • Polycystic kidney
  • Staghorn calculi and stones of smaller size
  • Anatomic abnormalities
  • Tumor resting on the bladder or ureter

In cases with a high WBC/no growth result, it is important to look for microorganisms during urinalysis or examination of a gram stain (test code 497). If microorganisms are observed but not recovered from routine culture, it is appropriate to culture for anaerobes and more slowly growing organisms, especially if the patient has a chronic urinary tract infection or anatomic abnormality. Please go to this link for further details on how to submit a specimen for these studies: http://questdiagnostics.com/directoryofservices/index.html.

Question 5. When should multiple or follow-up urine cultures be performed?

More than one urine culture may be required to establish a diagnosis of urinary tract infection. Factors such as timing of specimen collection, excessive fluid intake, and contaminated midstream urine can affect culture results.

Reculturing to prove bacteriologic cure is not recommended. However, if symptoms do not resolve or if symptoms recur, a subsequent urine culture may be performed. Follow-up cultures may be appropriate for pregnant women and patients at high risk for renal damage, even when they are asymptomatic. Note that in pediatric patients, fever beyond 48 hours is common in spite of negative follow-up urine cultures.

Question 6. What is the recommended time interval for a follow-up culture?

Follow-up cultures are recommended at 1-2 weeks after completion of therapy.

References

  1. McCarter YS, Burd EM, Hall GS, et al. Cumitech 2C, Laboratory diagnosis of urinary tract infections. Washington, DC: ASM Press; 2009.
This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.
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