In general, a positive dipstick urinalysis alone will not reliably rule in UTI. Positive nitrite findings, however, have a positive likelihood ratio of 13.3, making this parameter quite robust in diagnosing UTI. Positive nitrite findings alone on urinalysis are very specific (94%-98%) but have a sensitivity of only 34%-42%; this decreases the value of this measurement in the absence of other positive tests. Microscopic analysis (Figure 3) is also helpful in guiding diagnosis; a white blood cell count of more than 50 per high-power field yields a positive likelihood ratio of 6.4, the presence of bacteria from few to many yields one of 2-21.9, and the presence of more than 5 red blood cells per high-power field yields one of 2.
Given the strong post-test probability (77%) of the constellation of symptoms, including dysuria and frequency with the absence of vaginal discharge or irritation, diagnosis and empirical treatment of UTI, even in the face of negative urinalysis findings, is reasonable.
Another acceptable alternative is to collect a urine assay and wait to treat on the basis of the results. Many UTIs are self-limited without treatment; therefore, the risks for side effects need to be weighed against the benefits of treatment.
The differential diagnosis in a young, sexually active woman with abdominal pain and dysuria must include pelvic symptoms, especially if such factors as vaginal discharge, a history of unprotected sex, or new or multiple sexual partners are reported. Therefore, in a patient such as this, a pelvic examination is warranted as an additional step in the diagnostic algorithm.
Objective findings of vaginal discharge, malodor, cervical lesions, cervical motion tenderness, adnexal tenderness, or adnexal mass lower the post-test probability of UTI; however, given positive symptoms of UTI, the post-test probability is still not nil. Therefore, a urine assay (as well as tests for GC/chlamydia, the most common causes of cervicitis and PID) will aid in the diagnosis. Hematuria as a presenting symptom is much less likely in pelvic symptoms than in cystitis.
Reliably differentiating pyelonephritis from uncomplicated UTI can be difficult. The data are limited. Some clinical features are more suggestive of pyelonephritis, including chills, nausea and vomiting, tachycardia, tachypnea, bandemia, fever, and costovertebral angle tenderness, although the latter two are also associated with simple cystitis. One common clinical definition of pyelonephritis is the constellation of high fever, UTI symptoms, positive urine assay findings, and costovertebral angle tenderness.
The risk factors for pyelonephritis include an immunocompromised state, pregnancy, neoplasia, collagen disease, nephrolithiasis/obstruction, and reflux. Upon microscopic urinalysis, white blood cell casts are found exclusively in pyelonephritis.
Also in the differential diagnosis is nephrolithiasis. Hematuria is the common presenting symptom, and in this case, hydronephrosis also might suggest an obstructing stone; however, the patient did not have some of the features typical of nephrolithiasis, namely sudden onset of intense flank pain radiating to the groin. Patients at risk for nephrolithiasis include those at risk for dehydration; those with lower calcium intake; and those with granulomatous diseases, obesity, type 2 diabetes mellitus, and recurrent UTI.
The prevalence of asymptomatic bacteriuria in young women is approximately 5%; however, in women with at least one symptom of UTI, the prevalence increases to 50%. Therefore, in women presenting to a healthcare facility with symptoms of UTI, the pretest probability itself is about 50%.
In this case, the patient's concomitant symptoms and examination finding of increased vaginal discharge result in a relatively lower post-test probability of UTI (23%). With equivocal urinalysis findings, this warrants a urine assay to make the diagnosis.
In a patient without vaginal discharge, a report of dysuria, frequency, and hematuria has a post-test probability of 81% for UTI. If vaginal discharge is not reported, empirical UTI treatment is appropriate.
The most common complication of cystitis in young, nonpregnant women is pyelonephritis. Rarely, this upper UTI can progress to sepsis, acute renal failure, and multiorgan failure.
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Cite this: Melanie Malloy, Richard H. Sinert. ED Case Challenge: After New Sexual Partner, Dysuria, Discharge in a 21-Year-Old - Medscape - Aug 11, 2022.