Boring Questions: Do you even dip?

In Clinical Questions by Eve Purdy2 Comments

Urine is boring so we are doing a follow up post to Brent’s first ever post on BoringEM “Urinalysis Voodoo”. Less voodoo, more evidence.

The case:

Jane, a 23-year-old, sexually active female presents to the emergency department with a two day history of dysuria and urinary frequency. She has not experienced vomiting, fevers or changes in vaginal discharge. Her abdominal review of systems is negative. Her LMP was one week ago and she has had no new sexual partners in the past year. She has had one previous UTI two years ago. Her vital signs are normal and she has a temperature of 36.7. On abdominal exam she has mild suprapubic tenderness and no CVA percussion tenderness. Clinically, you suspect a urinary tract infection. Her urine dip is negative for nitrites, blood, but positive for leukocyte esterase.The clinical question:

The clinical question:

Does a negative urine dip rule out a urinary tract infection in the presence of isolated lower urinary tract symptoms in an otherwise healthy, young female?

The Search Strategy: 

Search terms input to Pubmed and Google Scholar were:

  • “Test characteristics AND urine dip”
  • “sensitivity AND urinalysis”
  • “negative predictive value OR positive predictive value AND urinalysis”.

These terms were also searched with “systematic review” in Google scholar. The references of relevant papers were also reviewed. “Urinary tract infection” was searched in the The Cochrane Review Database but no relevant article on diagnosis was found.

The Evidence:

Pre-test probability: a JAMA systematic review [1] estimated that when a woman presents with one symptom of a UTI the baseline probability of infection is 50%. The review went on to outline the likelihood ratios (LR) associated with the presence and absence of symptoms associated with diagnosis.

  • Increase likelihood of UTI: dysuria (LR=1.5), frequency (LR=1.3), hematuria (LR=2.0) and back pain (LR=1.6).
  • Decrease likelihood of UTI: absence of dysuria (LR=0.5), absence of back pain (LR=0.8), history of vaginal discharge (LR=0.3), history of vaginal irritation (LR=0.2).
  • Non-contributory: Fever, abdominal pain, flank pain

*Jane’s pertinent positives and negatives, give her a pre-dipstick probability for a UTI of just over 50% (using Fagan nomogram to adjust  calculate post test probability with LR 1.5 and 1.3 for associated symptoms).

Test characteristics: A large systematic review [2] of 51 studies evaluated the combined test characteristics of leukocyte esterase/nitrites and two more recent studies [3,6] examined the test characteristics of each test independently.

 

ParameterSensitivitySpecificityLR (+)LR (-)
Leukocyte esterase and/OR Nitrite75%82%4.10.3
Leukocyte esterase44.2%85.2%2.90.53
Nitrite27.9%99.7%270.73

 Post-test probability

  • Because of the high pre-test probability even a negative dipstick does not rule out a urinary tract infection.

NB: Jane’s urine dip was negative giving her a post-test probability of just over 30% (using Fagan nomogram to calculate post-test probability with LR(-) 0.3).

The Bottom Line: 

Urine dipstick analysis does not have a high enough negative LR to rule out urinary tract infection in those with a clinically high pre-test probability [6]. We will treat Jane’s symptoms with a short course of antibiotics and will not culture her urine [4, 5] something we would consider with any features suggesting a complicated infection, pyelonephritis or if she had recent antimicrobial treatment.

 

The not so boring question:

If the test is not going to change management then why do we continue to order it in this specific population?

 

Other FOAM on this topic

  • Best Bets “Accuracy of negative dipstick urinalysis in ruling out urinary tract infection in adults.”
  • Abbo et al. “Antimicrobial stewardship and urinary tract infections”
  • Brent Thoma’s first ever post on BoringEM “Urinalysis Voodoo

References

  1. Bent S, Nallamothu BK, Simel DL et al. Does this woman have an acute uncomplicated urinary tract infection? JAMA 2002;287(20):2701-2710. PMID: 12020306.
  2. Hurlbut T, Littenberg B. The diagnostic accuracy of rapid dipstick tests to predict urinary tract infection. Am J Clin Pathol.1991;96:582-588. PMID: 1951183.
  3. Schulz, T., Machado, M. J., Treitinger, A., Fiamoncini, A., & de Oliveira Niederauer, L. M. (2014). Risk associated with dipstick urinalysis for diagnosing urinary tract infection. pinnacle biochemistry research. Accessed at: http://www.researchgate.net/publication/260870381_Risk_associated_with_dipstick_urinalysis_for_diagnosing_urinary_tract_infection
  4. Takhar, S. S., & Moran, G. J. (2014). Diagnosis and Management of Urinary Tract Infection in the Emergency Department and Outpatient Settings. Infectious disease clinics of North America, 28(1), 33-48. PMID: 24484573
  5. Johnson, J. D., O’Mara, H. M., Durtschi, H. F., & Kopjar, B. (2011). Do urine cultures for urinary tract infections decrease follow-up visits?. The Journal of the American Board of Family Medicine, 24(6), 647-655.

Reviewing with the Staff (James Ahn)

Eve Purdy presents a compelling argument for discarding the urine dipstick when we have a high clinical pretest probability for a urinary tract infection (UTI). This is a viable strategy when approaching young and non-pregnant women who are otherwise healthy. If the sensitivity of a urine dipstick is not robust enough to dissuade treatment, then why waste the time and money?

UTIs are one of the most common infections seen in emergency department (ED). This is not an infrequent diagnosis; in the uncomplicated patient, UTIs should be rapid dispositions from the ED. A patient with a high pre-test clinical probability for UTI should be empirically treated with antibiotics. This strategy circumvents the need for urine from the emergency department, which at times can be harder to obtain than CSF! In the ED, the most precious resource is bed space, and any measure we can develop to increase turnover in a safe manner should be considered. Further, preforming a urine dip cost money to the patient and hospital, as well as provide a distraction to allied health professionals from other tasks.

In summary, the young, uncomplicated, and non-pregnant female who has high-risk factors for a UTI should be treated with antibiotics without the performance of a urine dip. The urine dipstick still holds a place in our diagnostic armamentarium for other patient populations and those who do not have such compelling historical risk factors.

Thanks to Jody Stasko for reviewing this post and to Rodrigo Cavalcanti for flagging an error in the case. It has been fixed to align the case with the calcuations.

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Eve Purdy

Eve Purdy

Senior Editor at BoringEM
Senior emergency medicine resident and anthropology student-happily consuming, sharing, creating and researching #FOAMed.
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