Laboratory Tests and Ancillaries
Urinalysis with microscopic examination and urine culture and sensitivity testing should be performed before, during and after therapy. It must also be noted that urine culture is the recommended method to identify clinically significant bacteriuria in patients suspected of having complicated UTI. Significant bacteriuria in women is defined as ≥10⁵ colony-forming units (cfu)/mL in a midstream urine (MSU) sample or >10⁴ cfu/mL in a straight catheter urine sample, whereas in men it is defined as ≥10⁴ cfu/mL in an MSU or straight catheter urine sample. In asymptomatic patients, significant bacteriuria is defined as two consecutive urine samples showing ≥10⁵ cfu/mL taken at least 24 hours apart in females with the same bacterial species and one sample in males.
Pyuria is defined as white blood cells (WBC) ≥10/mm³. This is present in almost all cases of UTI; its absence suggests an alternative diagnosis. The dipstick method is used for routine assessment, including the leukocyte esterase test, hemoglobin and nitrite reaction. Other tests include a pregnancy test, which is recommended for women of childbearing age when pregnancy cannot be ruled out based on medical history, and blood cultures, which may be indicated for patients presenting with sepsis or severe illness or when Staphylococcus aureus is isolated from the urine.
Urine Sample for Culture and Sensitivity
A urine specimen for culture and susceptibility testing should be obtained prior to the administration of antibiotics. The choice of antibiotic should be re-evaluated once culture results become available. Therapy should be guided by urine culture and sensitivity testing results and local resistance patterns to avoid the emergence of resistant strains.
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Imaging
Most patients with complicated UTI do not warrant imaging unless they are severely ill, unresponsive to therapy or with suspected underlying conditions. Additionally, imaging of the urinary tract should be undertaken to evaluate for hydronephrosis, stone disease and urinary tract abnormalities. Plain abdominal radiographs may be useful to evaluate for abnormal calcifications, renal contour and gas patterns. While an intravenous (IV) pyelogram provides radiographic images of the bladder, kidneys and ureters to determine the extent of urinary obstruction. A voiding cystourethrogram is used for evaluation of the neurogenic bladder and urethral diverticulum and to determine the presence of vesicoureteral reflux, whereas renal ultrasonography is an extremely valuable tool to evaluate for hydronephrosis, pyonephrosis and perirenal abscesses. It must be noted that a computed tomography (CT) scan is more sensitive for nephrolithiasis and for defining renal and suprarenal pathology. Lastly, cystoscopy may be done for convenient inspection of the urethra and the bladder.
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