What investigations are necessary to confirm a diagnosis of pyelonephritis in a patient presenting with flank pain and fever?

Investigations necessary to confirm a diagnosis of pyelonephritis in a patient presenting with flank pain and fever include:

• Urine analysis with dipstick testing for leukocyte esterase and nitrites to detect infection; a positive result supports the diagnosis of urinary tract infection (UTI) which may be upper tract (pyelonephritis) if systemic symptoms are present.
• Urine culture to identify the causative organism and guide antibiotic sensitivity, especially important if the patient is at higher risk or symptoms are severe.
• Clinical assessment for systemic signs such as fever ≥38°C and flank pain or tenderness, which alongside bacteriuria, supports acute upper UTI (pyelonephritis).
• Blood tests including inflammatory markers and renal function may be considered to assess severity and complications.
• Imaging (such as ultrasound) is not routinely required to confirm diagnosis in uncomplicated cases but should be considered if the patient is atypical, has recurrent infections, or does not respond to treatment.

In adults, the diagnosis is primarily clinical supported by urine testing; imaging and further investigations are reserved for complicated or atypical cases or if there is suspicion of structural abnormalities or complications.

Therefore, the essential investigations to confirm pyelonephritis are urine dipstick and culture combined with clinical features of fever and flank pain. Imaging and blood tests are adjuncts based on clinical judgement.

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