What is the first step in evaluating a child with nocturnal enuresis (bed wetting), polydipsia (excessive thirst) and polyuria (frequent urination)?

Initial Diagnostic Test for Nocturnal Enuresis with Polydipsia and Polyuria

Perform urinalysis immediately as the first diagnostic test—this is the sole obligatory laboratory investigation and will screen for diabetes mellitus, urinary tract infection, and kidney disease. 1, 2

Why Urinalysis is the Correct First Step

The combination of nocturnal enuresis with excessive thirst and drinking represents red flag symptoms that require metabolic investigation, not behavioral attribution. 2 The urinalysis serves as a critical screening tool that guides all subsequent management:

Immediate Screening Capabilities

• Urinalysis with dipstick provides point-of-care detection of glycosuria, which mandates urgent blood glucose testing to exclude diabetes mellitus. 2
• A negative dipstick for leukocyte esterase and nitrite has 95-98% negative predictive value for urinary tract infection, making it highly reliable for ruling out infection. 1, 2
• First-morning urine specific gravity helps distinguish between different causes of polyuria, including diabetes insipidus, diabetes mellitus, and primary kidney disease. 2

Why Other Options Are Incorrect

• Random blood glucose (Option B) is premature without first documenting glycosuria on urinalysis, which provides immediate screening and guides whether urgent glucose testing is needed. 2
• Urine culture (Option C) is not the first step—it should only be sent if the urinalysis suggests infection or if clinical suspicion remains high despite negative screening. 1
• Ultrasound (Option D) has no role in initial evaluation unless structural abnormalities are suspected based on history, physical examination, or urinalysis findings. 1

Critical Clinical Context

Polydipsia as a Warning Sign

The presence of polydipsia signals that children with polyuria due to diabetes or kidney disease need further investigation beyond simple enuresis evaluation. 1 This symptom pattern should never be dismissed as behavioral, as it may represent:

• Type 1 diabetes mellitus with osmotic diuresis from hyperglycemia 2
• Diabetes insipidus (central or nephrogenic) with vasopressin deficiency or resistance 3
• Chronic kidney disease with impaired concentrating ability 1

The Diagnostic Algorithm After Urinalysis

Once urinalysis is completed, the results determine next steps:

• If glycosuria is present: Obtain immediate blood glucose (fasting or random) to diagnose diabetes mellitus 2
• If specific gravity is persistently low (<1.005): Consider diabetes insipidus and proceed with water deprivation testing 3
• If proteinuria or hematuria is present: Evaluate for kidney disease with serum creatinine and renal function tests 1
• If pyuria or positive nitrites: Send urine culture and treat urinary tract infection 1

Common Pitfalls to Avoid

• Never attribute bedwetting with polydipsia to behavioral causes without metabolic workup—this combination represents a red flag requiring investigation. 2
• Do not skip urinalysis and proceed directly to blood tests—the urinalysis provides essential screening information that guides subsequent testing. 1
• Do not assume simple enuresis when excessive thirst is present—this symptom pattern suggests systemic disease until proven otherwise. 1, 2

Additional Baseline Evaluation

After urinalysis, complete the initial assessment with:

• Frequency-volume chart for 2 weeks to objectively document fluid intake and urine output patterns 1, 2
• Thorough physical examination focusing on growth parameters, blood pressure, abdominal palpation for bladder distention, and neurologic assessment 1
• Assessment for constipation, which commonly coexists with enuresis and may contribute to symptoms 1

The answer is A: Urinalysis is the mandatory first diagnostic test. 1, 2