What is the role of Ultrasound (USG) for Urinary Tract Infection (UTI) diagnosis?

From the Guidelines

Ultrasound (USG) is not typically recommended for diagnosing uncomplicated urinary tract infections (UTIs) but may be considered in cases of recurrent UTIs, complicated infections, or suspected anatomical abnormalities. According to the American College of Radiology Appropriateness Criteria for recurrent lower urinary tract infections in females 1, imaging is of low yield in patients without underlying risk factors, with less than two episodes per year on average, and who respond promptly to appropriate therapy. The guidelines suggest that imaging should not be routinely obtained in the index patient presenting with recurrent UTIs because of the low yield of anatomic abnormalities 1. However, in patients with recurrent UTIs, defined as at least three episodes of infection within the preceding 12 months, USG may be indicated to detect underlying structural issues that might contribute to recurrent infections, such as vesicoureteral reflux or urinary retention 1.

When considering USG for UTI diagnosis, it is essential to evaluate the patient's symptoms, medical history, and risk factors for complicated UTIs, such as anatomical abnormalities, prior urinary tract surgery or trauma, or underlying conditions like diabetes or immunosuppression 1. In cases where USG is performed, it can help identify underlying structural issues, detect hydronephrosis, identify stones, masses, or abscesses, and assess bladder emptying 1. The procedure is non-invasive, radiation-free, and takes about 30 minutes, making it a valuable diagnostic tool in specific situations.

Key points to consider when evaluating the need for USG in UTI diagnosis include:

• The patient's symptoms and medical history
• The presence of underlying risk factors for complicated UTIs
• The frequency and severity of recurrent infections
• The response to previous treatments and the presence of any underlying structural issues
• The potential benefits and limitations of USG in diagnosing and managing UTIs, as outlined in the American College of Radiology Appropriateness Criteria 1.

From the Research

Ultrasound for Urinary Tract Infections (UTIs)

• Ultrasound can be used to diagnose upper urinary tract infections, particularly to rule out obstructed pyelonephritis requiring emergency drainage of urine 2.
• A sonogram carried out within 48 hours is usually sufficient for this purpose 2.
• However, in complicated cases or those affecting already weakened areas, an urgent CT scan may be necessary, preferably after injection of iodinated contrast medium if renal function permits 2.

Diagnosis of UTIs

• The diagnosis of uncomplicated cystitis (bladder infection) and pyelonephritis (kidney infection) is usually easily made based on clinical presentation 3.
• Symptoms of UTIs may include dysuria, frequency, urgency, and presence or absence of vaginal discharge 4.
• Dipstick urinalysis can be used to aid in diagnosis, but results must be interpreted in context of the patient's pretest probability based on symptoms and characteristics 4.
• Urine culture is the gold standard for detection of UTI, but asymptomatic bacteriuria is common and should not be treated with antibiotics 4.

Treatment of UTIs

• First-line treatments for UTI include nitrofurantoin, fosfomycin, and trimethoprim-sulfamethoxazole (when resistance levels are <20%) 4.
• Antimicrobial resistance is increasing, and individualized assessment of risk factors for resistance and regimen tolerability is needed to choose the optimum empirical regimen 5.
• Immediate antimicrobial therapy is recommended rather than delayed treatment or symptom management with ibuprofen alone 5.
• In pregnancy, beta-lactams, nitrofurantoin, fosfomycin, and trimethoprim-sulfamethoxazole can be appropriate treatments 4.

Complicated UTIs

• Complicated UTIs, such as those occurring in patients with anatomic abnormalities, stone, or immunosuppression, are often caused by organisms other than E. coli, and long-term antibacterial therapy may be necessary 6.
• In cases of complicated UTIs, CT scanning is essential to investigate whether there are complications and to diagnose unusual and rare forms of pyelonephritis 2.