Most Appropriate Next Investigation
The most appropriate next investigation is B- Random glucose, as the triad of bedwetting, weight loss, and polydipsia is a medical red flag for diabetes mellitus that demands immediate blood glucose testing. 1, 2, 3
Clinical Rationale
This presentation represents classic symptoms of hyperglycemia that require urgent diagnostic evaluation for diabetes mellitus, not screening but diagnostic testing. 2 The combination of these three symptoms—nocturnal enuresis, unexplained weight loss, and polydipsia—is explicitly identified by multiple guideline organizations as indicating potential diabetes that must be ruled out immediately. 1, 2, 3
Why Random Glucose is the Correct Answer
A random plasma glucose ≥200 mg/dL in the presence of classic symptoms (polyuria/polydipsia and unexplained weight loss) is sufficient to diagnose diabetes mellitus without requiring fasting or additional testing. 4, 2, 5
Random glucose testing provides immediate diagnostic information and can confirm diabetes in a single test when symptoms are present, whereas other options either delay diagnosis or address the wrong disease process. 2
The American Diabetes Association criteria specify that symptoms of hyperglycemia with a casual plasma glucose ≥200 mg/dL (11.1 mmol/L) are diagnostic for diabetes. 4
Why Other Options Are Incorrect
Option A (Urinalysis and Culture) - Wrong Sequence
While urine dipstick testing to detect glycosuria is recommended as part of the initial evaluation, it is a screening step that must be followed immediately by blood glucose testing if positive. 1, 3
Urinalysis alone cannot diagnose diabetes and delays definitive diagnosis. 1
The presence of glycosuria on dipstick mandates immediate blood glucose measurement to confirm diabetes. 3
Option C (Psychiatric Referral) - Dangerous Error
Do not dismiss this presentation as psychogenic polydipsia without first ruling out systemic disease. 1, 2, 3
The American Academy of Pediatrics explicitly warns against dismissing the combination of weight loss, polydipsia, and enuresis as a primary psychiatric or behavioral problem. 2, 3
Delaying glucose testing can lead to progression to diabetic ketoacidosis, a life-threatening complication. 1, 2
Option D (Renal Ultrasound) - Premature and Wasteful
Do not order renal ultrasound or other expensive imaging before basic screening tests, as this wastes resources and delays diagnosis. 1, 3
The International Children's Continence Society explicitly recommends against routine renal ultrasound in enuresis, stating it is only indicated after initial screening identifies specific risk factors such as history of UTI, hematuria, urolithiasis, or renal insufficiency detected on initial testing. 2, 3
Imaging should never precede basic metabolic evaluation in this presentation. 1
Clinical Management After Diagnosis
Youth with marked hyperglycemia (blood glucose ≥250 mg/dL, A1C ≥8.5%) who are symptomatic with polyuria, polydipsia, nocturia, and/or weight loss should be treated initially with basal insulin while metformin is initiated and titrated. 4
If ketosis or ketoacidosis is present, treatment with subcutaneous or intravenous insulin should be initiated immediately to correct the hyperglycemia and metabolic derangement. 4
Critical Pitfall to Avoid
The single most dangerous error is delaying blood glucose testing in favor of other investigations. This presentation demands immediate glucose measurement because the duration of hyperglycemia is a predictor of adverse outcomes, and delayed diagnosis can result in diabetic ketoacidosis. 1, 2, 6