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Improving Urine Culture Results

Two steps are critical to reduce this normal flora problem. Step 1: Proper urine specimen collection & Step 2: Proper urine specimen transport to the laboratory. The clean catch, mid-stream collection procedure is essential for limiting the number of normal flora bacteria introduced into the specimen during collection, and the urine preservative, boric acid, is essential for optimal urine specimen transport.

The boric acid urine preservative has two benefits:

  • It limits or prevents the growth of normal flora bacteria thus controlling contamination of urine samples.
  • Boric acid protects and preserves pathogens in urine samples so that they are more readily detected in cultures.


  • After collection, the urine should be poured into a boric acid tube to about half an inch (1 cm) from the top.
  • A minimum of 5 ml urine is required.
  • Replace and tighten cap securely to prevent leakage.
  • Urine specimens are stable in boric acid for up to 24 hrs, but should still be transported to the laboratory as quickly as possible. The sooner the urine specimen can be cultured, the better the results.

Dr. Michael T. Kelly, Head of Medical Microbiology

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