• Urgent
• Features of renal colic or suspicion of renal stones +/– renal tract obstruction (plain X-ray and CT KUB)

As soon as possible (renal ultrasound is the usual initial investigation):

• Acute kidney injury
• Pyelonephritis in men or children
• Recurrent episode of pyelonephritis in women
• History of renal pathology
• Persistent fever despite 48–72 h of appropriate antibiotic
• Uncertain diagnosis, for example considering genitourinary pathology or appendicitis

Referral for renal tract imaging post treatment of acute infection

• Urinary infection in boys and men with no known risk factors for UTI
• Recurrent urinary tract infections (>3/year)
• Haematuria

Not indicated

• Uncomplicated lower tract infection in women
• First episode of pyelonephritis in women with no AKI and rapid treatment response (within defervescence within 48–72 h)