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13 Culture

You tell Jan that the lab findings indicate either a urinary tract infection or inflammation.  You think that the best way to proceed is to culture the urine and then prescribe an antibiotic if warranted based on culture results. 

She responds by saying, “If you’re going to give me an antibiotic anyway, why waste my money and culture the urine?  Besides, I will be lucky if I can even get Nemo to take pills.” 




Diagnostic vs. Therapeutic Urine Cultures


What are diagnostic urine cultures?

  • Quantitative urine cultures before initiating antibiotic therapy is considered to be the gold standard for diagnosis of bacterial urinary tract infections (UTI).
  • Diagnostic urine cultures provide accurate identification of specific bacterial species and aids in the selection of antibiotics.  It also facilitates differentiation of recurrent UTIs caused by relapses from recurrent UTIs caused by reinfections.
  • If a patient is currently being treated with an antibiotic, it should be discontinued for 3-5 days before diagnostic urine culture to minimize inhibition of bacterial growth. 

What are therapeutic urine cultures?

  • Culture of urine at strategic times during antibiotic therapy (“therapeutic urine cultures”) is an effective method of assessing therapy.  Therapeutic cultures are essential for determining why a patient may not be responding to treatment.
  • For patients with a high risk of morbidity and mortality (eg, prostatitis, pyelonephritis, immunosuppression, and urinary tract obstruction), evaluation of urine culture and urinalysis 3-5 days after initiating therapy allows for verification of antibiotic effectiveness before the development of irreversible organ damage or systemic spread of disease.  The same strategy should be considered when prescribing antibiotics with a high risk of toxicity.

Benefits of therapeutic urine cultures:

  1. Timely test of antibiotic efficacy
  2. Verification of proper antibiotic administration
  3. Early detection of bacterial resistance to antibiotics
  4. Timely detection of persistent infections
  5. Provision of justification for early discontinuation of potentially toxic antibiotics

Suggested times to culture urine to diagnose and monitor persistent urinary tract infections:

I.    Diagnostic

  •     Before administration of therapy


II.    Therapeutic

  •     3 to 5 days after initiating therapy
  •     Any time clinical signs of laboratory abnormalities recur during therapy
  •     Before discontinuing therapy


III.    Surveillance

  •     7 to 14 days after stopping therapy
  •     1 to 2 months after stopping therapy
  •     3 to 6 months after stopping therapy
  •     Any time clinical signs recur























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