What is the role of urinary studies in the diagnosis of urinary tract infection (UTI) in males?

Updated: Aug 27, 2019
  • Author: John L Brusch, MD, FACP; Chief Editor: Michael Stuart Bronze, MD  more...
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Answer

Urine specimens may be obtained by suprapubic aspiration, catheterization, or midstream clean catch. Most males can perform a midstream clean catch reasonably well, with a reliability approaching that of suprapubic aspiration. Uncircumcised men must retract the prepuce and cleanse the glans before obtaining a specimen. If the patient is unable to cooperate, a catheterized specimen or suprapubic aspiration is necessary.

Bacteriuria without pyuria suggests contamination or colonization. Pyuria without bacteriuria suggests nongonococcal urethritis (NGU), genitourinary tuberculosis, stone disease, or malignancy.

If a Gram stain of an uncentrifuged clean-catch midstream urine sample reveals the presence of 1 bacterium per oil-immersion field, this represents 10,000 bacteria/mL of urine. A specimen (5mL) that has been centrifuged for 5 minutes at 2000 revolutions per minute (rpm) and examined under high power after Gram staining allows for the identification of bacteria in lower numbers. In general, Gram staining has a sensitivity of 90% and a specificity of 88%.

Urine culture remains the criterion standard for the diagnosis of UTI. Collected urine should be immediately sent for culture; if not, it should be refrigerated at 4°C. Two culture techniques (dip slide, agar) are used widely and are accurate.

The exact number of bacteria in a urine culture that is needed to define UTI in a man is a bit controversial; generally, positive results are seen if there are more than 1000 colony-forming units (CFU)/mL of urine, much lower than the threshold for women. [8] However, most authors would accept a value of more than 10,000 CFU/mL. Some advocate the treatment of any pathogens growing in a patient with symptoms of UTI.


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