Tests
1st tests to order
dipstick urinalysis (U/A)
Test
Either pyuria or nitrites may correspond to infection, but the presence of both improves the specificity to >90%.[61]
Conversely, if both are negative, the test accurately predicts the absence of infection. One Denmark study of patients presenting to the emergency department found both a negative leukocyte esterase and negative nitrite had a negative predictive value of 93.3% for men.[55]
In the nursing home setting, U/A is less reliable in predicting the presence of infection, because a high proportion of these patients have pyuria related to asymptomatic bacteriuria.[6][16] Therefore, do not obtain U/A in older adults unless there are signs or symptoms suggestive of urinary tract infection (UTI) as this can lead to unnecessary antibiotic prescribing.[2][6][56] Furthermore, a positive U/A in asymptomatic older patients may lead to an incorrect assumption that an acute change of mental status is caused by a UTI, delaying the detection of an alternative source of infection.[56] Also, U/A is not reliable in determining the presence of catheter-associated UTI.[25]
Dipstick should not be used to diagnose UTI in patients with long-term indwelling catheters.[60]
Result
positive leukocyte esterase and/or nitrite
urine microscopy
Test
Will help confirm the finding of leukocytes and can identify the presence of bacteria. One trial identified 10 WBC/mm³ as having 71% sensitivity and 76% specificity.[58]
Result
leukocytes and/or bacteria
urine culture
Test
A value of ≥10³ colony-forming units (CFU)/mL of one, or predominantly one, organism provides a sensitivity of 97% in symptomatic men.[52][75]
Midstream clean-catch urine used for culture is appropriate, with a sensitivity and specificity similar to bladder urine obtained by suprapubic aspiration and urethral catheterization.[58]
In patients with indwelling catheters, a urine dipstick should not be used to diagnose urinary tract infection (UTI), as catheters are usually colonized with bacteria and will likely give a positive result. Instead, a urine culture is used to support the diagnosis in a symptomatic patient.[60]
Do not order urine cultures unless patients have symptoms consistent with UTI as routine culture of asymptomatic individuals may detect asymptomatic bacteriuria.[56][59] Testing for asymptomatic bacteriuria should only be pursued in specific patients such as those who are about to undergo endoscopic urologic procedures associated with mucosal disruption.[6]
Result
≥10³ CFU/mL
Gram stain
Test
May help in determining initial empiric antibiotic therapy; however, the accuracy is limited.
Like U/A, Gram stain better predicts the absence of infection but does not confirm the presence of urinary tract infection.
One trial analyzing 4900 specimens identified the sensitivities for gram-positive cocci and gram-negative rods as 63% and 45%, respectively; and specificities as 91% and 94%, respectively.[23]
Result
bacteria
Tests to consider
CT renal tract
Test
Provides excellent anatomic detail and is the best test for identifying perirenal abscess.
Should be reserved for those who have voiding dysfunction without a clearly identifiable cause such as benign prostatic hyperplasia (BPH), in cases of treatment failure, suspicion of obstruction or complication, or in those with signs of upper tract infection.[5][61][62][63]
The American College of Radiology recommends that CT urography and/or ultrasound of the kidneys and retroperitoneum be considered for further evaluation in patients with elevated creatinine, stones, hematuria, urinary tract infection, or other complicating history.[64][65]
Result
prostatic abscess, perirenal abscess, urinary calculi, tumors, or evidence of urinary tract obstruction
ultrasound
Test
Should be reserved for those suspected of having a structural abnormality without a clearly identifiable cause such as BPH, in cases of treatment failure, suspicion of obstruction or complication, or in those with signs of upper tract infection.[5][61][62][63]
The American College of Radiology recommends that CT urography and/or ultrasound of the kidneys and retroperitoneum be considered for further evaluation in patients with elevated creatinine, stones, hematuria, urinary tract infection, or other complicating history.[62][63]
Result
rules out obstruction, can note stones or masses, can evaluate if post-void residual remains elevated post voiding
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