Chapter 11 – “Urinary Tract Infection”
Welcome to the eleventh installment of “Inconceivable: medical terms that don’t mean what you think they mean.”
You are taking care of an alert and oriented 80-year-old woman who presented to your ED from an assisted living facility. She reports a few days of weakness and poor appetite, but her history including extensive ROS is otherwise frustratingly negative. Her temperature and heart rate are normal and her blood pressure is 149/84. She appears well but fatigued, and her physical exam is otherwise unremarkable. Her blood work reveals a mildly elevated bun/cr ratio and a normal CBC. Her urinalysis (UA) is notable for moderate leukocyte esterase, 10-25 WBC, and moderate bacteria. You diagnose her with a urinary tract infection and initiate antibiotics. Was your diagnosis correct? Read on to find out.
Clinicians across many specialties use the diagnosis “urinary tract infection” to refer to a certain set of urinalysis results, and others use the diagnosis to refer to certain colony forming units (CFU) on urine culture. These interpretations are highly variable because there are no clear UA reference ranges and no universal culture data cutoffs. Because of the inherent flaws of the UA, the diagnosis of UTI requires more than just the result of a test; one must also consider symptoms when making this diagnosis.
To properly diagnose a urinary tract infection, your patient must have:
- Subjective symptoms
- Urinalysis/culture evidence of UTI
If your patient has a positive urine culture without symptoms, then your patient has asymptomatic bacteriuria. Some resources advocate diagnosing UTI based on symptoms alone, but this strategy has a false-positive rate of 30-40%.
So, what exactly counts as “symptoms.” Weakness? Nausea? Fever? The best available data says no. Symptoms include dysuria, frequency, urgency, hesitancy, suprapubic pain, gross hematuria, suprapubic tenderness, flank pain, and/or costovertebral angle tenderness.
It follows, then, that the diagnosis is extremely difficult in patients who are unable to provide any history or whose clinical condition precludes clear symptoms. Patients with clear evidence of sepsis will receive broad spectrum antibiotics anyway, so there isn’t much controversy there. What about the patient with dementia who’s unable to reliably say whether he or she is experiencing symptoms? In these cases, you must carefully consider risks and benefits, but in general we probably over diagnose and over treat UTI in these patients as well. Keep in mind that it gets even cloudier when patients can give a reliable history but may have barriers to feeling urinary symptoms. Examples include patients with spinal cord injuries and those with neurogenic bladder from uncontrolled diabetes.
Why does this matter? In addition to the obvious risk of unnecessary antibiotic use (cost, resistance, C. diff, side effects to name a few), there is serious danger of premature closure. Getting distracted by and anchoring on an abnormal UA frequently ends a clinician’s investigation for the etiology of a patient’s weakness, altered mental status, or nausea. It becomes easy to miss the potentially dangerous silent MI, toxic ingestion, or even psychiatric illness. Do you think you correctly diagnosed the patient from earlier, with this new information would you have even checked a UA?
One final point is that there are two specific instances when the above discussion does not apply: pregnant women and pre-op urologic surgery patients.
Diagnosis of a urinary tract infection is not as simple as checking the urinalysis and culture. It also requires subjective symptoms or other evidence of an infection.
Askew K. Urinary Tract Infections and Hematuria. In: Tintinalli JE, Stapczynski J, Ma O, Yealy DM, Meckler GD, Cline DM. eds. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 8e New York, NY: McGraw-Hill; 2016. http://accessemergencymedicine.mhmedical.com.proxy.cc.uic.edu/content.aspx?bookid=1658§ionid=109433563. Accessed May 23, 2017.
Ducharme J, Neilson S, Ginn JL. Can urine cultures and reagent test strips be used to diagnose urinary tract infection in elderly emergency department patients without focal urinary symptoms? CJEM. 2007 Mar;9(2):87-92.
Hooton TM. Clinical practice. Uncomplicated urinary tract infection. N Engl J Med. 2012 Mar 15;366(11):1028-37.
Nicolle LE, Bradley S, Colgan R, Rice JC, Schaeffer A, Hooton TM; Infectious Diseases Society of America; American Society of Nephrology; American Geriatric Society. Infectious Diseases Society of America guidelines for the diagnosis and treatment of asymptomatic bacteriuria in adults. Clin Infect Dis. 2005 Mar 1;40(5):643-54. Epub 2005 Feb 4.
Dr. Krueger (@HoyaBadger) is currently an emergency medicine attending physician at Advocate Lutheran General Hospital, clinical instructor at UIC, and a former UIC EM Chief Resident.