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Urinary Tract Infection, Female: Differential Diagnoses & Workup

Author: David S Howes, MD, Residency Program Director, Professor of Medicine, Section of Emergency Medicine, University of Chicago/Pritzker School of Medicine
Contributor Information and Disclosures

Updated: Nov 20, 2009

Differential Diagnoses

Other Problems to Be Considered

Cervicitis
Chlamydia

Workup

Laboratory Studies

• If UTI is suspected, the initial test of choice is urinalysis.
  • An appropriate specimen must be collected.
  • The midstream-voided technique is as accurate as catheterization if proper technique is followed.
    • Instruct the woman to remove her underwear and sit facing the back of the toilet. This promotes proper positioning of the thighs.
    • Instruct patient to spread the labia with one hand and cleanse from front to back with povidone-iodine or soaped swabs with the other hand, then pass a small amount of urine into the toilet, and finally urinate into the specimen cup.
    • The use of a tampon may allow a proper specimen if heavy vaginal bleeding or discharge is present.
• Pyuria, as indicated by a positive result of the leukocyte esterase dip test, is found in the vast majority of patients with UTI. This is an exceedingly useful screening examination that can be performed promptly in any ED setting.
• However, appreciate that low-level pyuria (6-20 white blood cells [WBCs] per high power field [HPF] microscopy on a centrifuged specimen) may be associated with an unacceptable level of false-negative results with the leukocyte esterase dip test, as Propp et al found in an ED setting.¹
  • In the female with appropriate symptoms and examination findings suggestive of UTI, urine microscopy may be indicated despite a negative result of the leukocyte esterase dip test.
  • Current emphasis in the diagnosis of UTI rests with the detection of pyuria. As noted, a positive leukocyte esterase dip test suffices in most instances.
  • According to Stamm et al, levels of pyuria as low as 2-5 WBCs per HPF in a centrifuged specimen are important in the female with appropriate symptoms. The presence of bacteriuria is as significant.
  • A positive result on the nitrate test is highly specific for UTI, typically because of urease-splitting organisms, such as Proteus species and, occasionally, E coli; however, it is very insensitive as a screening tool, as only 25% of patients with UTI have a positive nitrite test result.
  • Low-level or, occasionally, frank hematuria may be noted in otherwise typical UTI; however, its positive predictive value is poor.
• Visual inspection of the urine is not helpful. Cloudiness of the urine is most often due to protein or crystal presence, and malodorous urine may be due to diet or medication use.
• Historically, the definition of UTI was based on the finding at culture of 100,000 colonies/mL of a single organism. However, this definition misses up to 50% of symptomatic infections, so the lower colony rate of greater than 1,000 colonies/mL is now accepted.²
  • Obtain a urine culture in patients suspected of having an upper UTI and a complicated UTI as well in those in whom initial treatment fails.
  • If the patient has had a UTI within the last month, relapse is probably caused by the same organism. Relapse represents treatment failure.
  • Re-infection occurs in 1-6 months and usually is due to a different organism (or serotype of the same organism). Obtain a urine culture for patients who are re-infected.
• A complete blood count (CBC) is not that helpful in differentiating upper from lower UTI or in making decisions regarding admission. However, leukopenia in hosts who are older or immunocompromised is an ominous finding.
• Renal function testing is not indicated in most episodes of UTI. It may be helpful in patients with known urinary tract structural abnormality or renal insufficiency. Renal function testing also may be helpful in older, particularly ill-appearing, hosts or in hosts with other complications.

Imaging Studies

• In the vast majority of patients with UTI, no imaging studies are indicated.
• If findings are suggestive of nephrolithiasis complicating the presentation, an intravenous pyelogram (IVP) or renal ultrasound should be obtained to exclude the possibility of obstruction or hydronephrosis.
• Recent studies with dynamic computed tomography (helical CT scan) are proving that this study provides information similar to that yielded by IVP without the need for dye injection. Dynamic CT scans also can serve as a convenient screen for abdominal aortic aneurysm masquerading as UTI or renal colic.
• Additional testing may be indicated if the diagnosis is in doubt. For example, a pelvic ultrasound may be indicated in a young woman with pelvic tenderness, cervical discharge, and unilateral adnexal tenderness to evaluate for a tubo-ovarian abscess; a CT scan may be indicated in the elderly patient whose presentation is not typical for UTI but who has abdominal pain, lower abdominal tenderness, and pyuria.

Procedures

• Catheterization is indicated if the patient cannot void spontaneously, if the patient is too debilitated or immobilized, or if obesity prevents the patient from obtaining a suitable specimen.
• Although less common than in older men, postvoiding residual urine volume, measurable by catheterization, may reveal urinary retention in a host with a defective bladder-emptying mechanism.

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