What is the initial evaluation step for a boy with nocturnal enuresis and polydipsia?

Initial Evaluation: Urine Analysis (Option A)

In a boy presenting with nocturnal enuresis accompanied by polydipsia and excessive thirst, immediate urine dipstick testing is mandatory to rule out diabetes mellitus and other metabolic disorders before any other investigation. 1

Why Urinalysis First

The combination of bedwetting with polydipsia and excessive drinking represents red flag symptoms that require immediate metabolic evaluation rather than standard enuresis workup. 1 Here's the algorithmic approach:

Critical Screening Function

• Urinalysis is the sole obligatory laboratory test in children with enuresis according to International Children's Continence Society guidelines 1
• Glycosuria on dipstick mandates immediate exclusion of diabetes mellitus and should prompt urgent blood glucose testing 1
• This test can be performed immediately in the office and may reveal a life-threatening condition that requires urgent intervention 1

Red Flag Recognition

• Polydipsia signals that children with polyuria due to diabetes or kidney disease need further investigation 2
• The history of "always thirsty and drinks a lot" distinguishes this case from simple monosymptomatic enuresis 2
• Children with diabetes must be detected when presenting with these symptoms 2

Why Not the Other Options Initially

FBS (Option B) - Second Step

While fasting blood sugar would ultimately be needed if glycosuria is detected, the urine dipstick provides immediate point-of-care screening and can be done without delay 1. The dipstick result will guide whether urgent blood glucose testing is needed 1.

Urine Culture (Option C) - Not Indicated

• Urine culture is appropriate when urinary tract infection is suspected 2
• However, the clinical presentation of polydipsia and excessive thirst points toward metabolic rather than infectious etiology 1
• A negative dipstick for leukocyte esterase and nitrite has 95-98% negative predictive value for UTI 2

Ultrasound (Option D) - Reserved for Specific Indications

• Renal ultrasound is pursued only with specific indications: continuous wetting, abnormal voiding pattern, or recurrent urinary tract infections 2
• This child's presentation suggests systemic metabolic disease rather than structural urological abnormality 1

Additional Evaluation After Urinalysis

Once diabetes is excluded or confirmed:

• Complete a frequency-volume chart to objectively document fluid intake and urine output patterns 3
• Assess for other causes of polyuria including diabetes insipidus, which can present with nocturnal enuresis and polydipsia 4, 5
• First-morning urine specific gravity can help distinguish between different causes of polyuria 2

Critical Pitfall to Avoid

Do not attribute bedwetting to behavioral causes when accompanied by polydipsia and excessive thirst—these are red flag symptoms requiring metabolic investigation. 1 Do not delay testing by ordering comprehensive metabolic panels or scheduling follow-up appointments first—the dipstick can be done immediately 1.