What is the initial evaluation for a child with nocturnal enuresis, polydipsia, and excessive thirst?

Initial Evaluation: Blood Glucose Testing is Essential

In a child presenting with nocturnal enuresis, polydipsia, and excessive thirst, you must immediately check blood glucose (either fasting or random) to rule out diabetes mellitus before pursuing standard enuresis workup. The combination of polyuria, polydipsia, and enuresis is a classic presentation of new-onset diabetes in children 1.

Why Blood Glucose Takes Priority

The triad of symptoms—bedwetting, excessive thirst, and drinking large amounts—strongly suggests diabetes mellitus rather than simple enuresis:

• Polyuria and polydipsia are hallmark presenting symptoms of Type 1 diabetes in children, reflecting osmotic diuresis from hyperglycemia 1
• These symptoms typically appear around age 10, which falls within the peak incidence range for Type 1 diabetes onset in childhood 1
• Diabetes insipidus can also present with nocturnal enuresis, polyuria, and polydipsia, and should be considered if diabetes mellitus is ruled out 2, 3

The Correct Answer: B (FBS) or C (Random Blood Glucose)

Either fasting blood glucose (FBS) or random blood glucose is appropriate as the initial test—both can diagnose diabetes mellitus effectively:

• Random blood glucose ≥200 mg/dL with symptoms confirms diabetes 1
• Fasting blood glucose ≥126 mg/dL confirms diabetes 1
• Random glucose may be more practical in a symptomatic child who doesn't need to wait for fasting state 1

Why Not Urinalysis First?

While urinalysis is the standard initial test for uncomplicated enuresis 4, this case is NOT uncomplicated enuresis:

• Standard enuresis guidelines recommend urinalysis to screen for urinary tract infection (95-98% negative predictive value) 4
• However, these guidelines explicitly state that polydipsia should prompt evaluation for endocrine disorders 4
• The 2022 European Urology guidelines specifically list "Have you been feeling excessively thirsty?" as a screening question for endocrine causes of nocturia 4
• Baseline investigations for nocturia with polydipsia should include HbA1c 4

Why Not Ultrasound?

Renal ultrasound is reserved for specific indications in enuresis 4:

• Continuous wetting (not just nocturnal) 4
• Abnormal voiding patterns 4
• Recurrent urinary tract infections 4
• Abnormal physical examination findings 4
• This child has none of these indications—the polydipsia points to a metabolic/endocrine cause, not a structural urological problem 4

Clinical Algorithm

Step 1: Check blood glucose immediately (random or fasting) 1

Step 2: If glucose is elevated:

• Confirm diabetes diagnosis with repeat testing or HbA1c 1
• Check for diabetic ketoacidosis if glucose is markedly elevated 5
• Initiate insulin therapy as needed 5

Step 3: If glucose is normal:

• Consider diabetes insipidus, especially with family history of enuresis or polyuria 2, 3
• Proceed with urinalysis to rule out urinary tract infection 4
• Obtain first-morning urine specific gravity (<1.015 suggests concentrating defect) 4

Critical Pitfall to Avoid

Do not dismiss polydipsia and polyuria as "just enuresis"—this delays diagnosis of potentially life-threatening diabetes mellitus 1. The mother's concern about excessive thirst and drinking is a red flag that distinguishes this from typical primary nocturnal enuresis, which occurs without daytime symptoms 4.