What is the most appropriate next investigation for a patient presenting with nocturnal enuresis (bedwetting), weight loss, and polydipsia (excessive thirst)?

Most Appropriate Next Investigation

The most appropriate next investigation is urine analysis (dipstick), followed immediately by random glucose measurement if glycosuria is detected. 1, 2

Clinical Reasoning

This triad of bedwetting, weight loss, and polydipsia represents a medical red flag that demands urgent evaluation for diabetes mellitus before considering any primary bladder disorder. 2, 3

Why Urine Dipstick First

• The International Children's Continence Society explicitly states that the sole obligatory laboratory test in children with enuresis is a urine dipstick test. 1
• Glycosuria on dipstick means diabetes mellitus must be immediately excluded. 1
• This is the fastest, most cost-effective screening tool that can be performed immediately in any clinical setting. 1
• Weight loss combined with polydipsia and enuresis indicates potential diabetes mellitus that must be ruled out immediately. 2, 3

Immediate Follow-Up Testing

• If glycosuria is present on dipstick, proceed immediately with blood glucose testing (random plasma glucose). 2, 3
• A random plasma glucose ≥200 mg/dL in a patient with classic symptoms (polyuria/polydipsia and unexplained weight loss) is sufficient to diagnose diabetes mellitus without requiring fasting or additional testing. 2, 4, 5
• If random glucose is elevated but <200 mg/dL, proceed with fasting plasma glucose or HbA1c for confirmation. 2

Why Other Options Are Incorrect

Random Glucose Alone (Option B)

• While ultimately necessary, skipping the urine dipstick misses the opportunity to detect proteinuria (kidney disease) and provides no information about urinary tract infection. 1
• The guideline-recommended sequence is dipstick first, then glucose if indicated. 1, 3

Psychiatric Referral (Option C)

• The American Academy of Pediatrics explicitly warns against dismissing the combination of weight loss, polydipsia, and enuresis as psychogenic polydipsia, as this triad demands investigation for systemic disease. 2
• Psychiatric referral before ruling out diabetes mellitus is a dangerous error that can lead to delayed diagnosis and progression to diabetic ketoacidosis. 2, 3

Renal Ultrasound (Option D)

• The International Children's Continence Society explicitly states that routine ultrasound of the kidneys and upper urinary tract is not warranted in enuresis. 1
• Renal ultrasound is only indicated after initial screening identifies specific risk factors such as history of UTI, hematuria, or renal insufficiency detected on initial testing. 2
• Ordering expensive imaging before basic screening tests wastes resources and delays diagnosis. 3

Critical Pitfalls to Avoid

• Do not delay urine and glucose testing, as this can lead to delayed diagnosis and progression to diabetic ketoacidosis. 2, 3
• Do not dismiss this presentation as simple primary enuresis without first ruling out systemic disease. 2, 3
• Do not order renal ultrasound or other expensive imaging before basic screening tests. 2, 3

Answer: A - Urine analysis and culture (though technically just dipstick is sufficient initially, with culture only if infection is suspected) 1