Investigations
1st investigations to order
dipstick urinalysis
Test
Either pyuria or nitrites may correspond to infection, but the presence of both improves the sensitivity to an overall range of 68% to 88%.[45][46]
Conversely, if both are negative, the test accurately predicts the absence of infection, with specificity ranging between 77% and 100% in all populations.[45][46]
In the nursing home setting, urinalysis is less reliable in predicting the presence of infection, because a high proportion of these patients have pyuria related to asymptomatic bacteriuria.[4][11] Also, urinalysis is not reliable in determining the presence of catheter-associated UTI.[16]
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.[46]
Result
leukocytes and/or bacteria
urine culture
Test
A value of ≥10² colony-forming units (CFU)/mL of one, or predominantly one, organism provides a sensitivity of 95% and specificity of 85% for UTI in symptomatic men.[50]
Midstream clean-catch urine used for culture is appropriate, with a sensitivity and specificity similar to bladder urine obtained by suprapubic aspiration and urethral catheterisation.[46]
As many as 40% of men in long-term care facilities will have ≥10⁵ CFU/mL growth of bacteria without symptoms related to the urinary tract (asymptomatic bacteriuria).[4]
Result
≥10² CFU/mL
Gram stain
Test
May help in determining initial empirical antibiotic therapy; however, the accuracy is limited.
Like urinalysis, Gram stain better predicts the absence of infection.
One trial analysing 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.[15]
Result
bacteria
Investigations to consider
CT renal tract
Test
Provides excellent anatomical 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, in men with persistent haematuria, or in those with signs of upper tract infection.[1][3]
Result
perirenal abscess, urinary calculi, or tumours
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, in men with persistent haematuria, or in those with signs of upper tract infection.[1][3]
Compared with intravenous urogram, ultrasound offers a better choice because it is non-invasive and does not require use of contrast agents.
Result
rules out obstruction
plain x-ray kidneys, ureters, and bladder (KUB)
Test
Not consistently reliable.
Should be reserved for those suspected of having a structural abnormality without a clearly identifiable cause such as BPH, in cases of treatment failure, in men with persistent haematuria, or in those with signs of upper tract infection.[1][3]
One study involving 114 men (average age 54) found that plain x-ray KUB combined with ultrasound compared favourably with intravenous urogram in identifying structural abnormalities of the urinary tract.[26]
Result
urinary tract stone, abscess
intravenous urogram (IVU)
Test
Should be reserved for those who have voiding dysfunction without a clearly identifiable cause such as BPH, in cases of treatment failure, in men with persistent haematuria, or in those with signs of upper tract infection.[1][3]
Plain x-ray KUB combined with ultrasound may perform as well as IVU.[26]
Result
rules out obstruction
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