Most Appropriate Next Investigation
The most appropriate next investigation is B. Random glucose, as the triad of bedwetting, weight loss, and polydipsia represents classic symptoms of hyperglycemia that demand immediate exclusion of diabetes mellitus before any other testing. 1
Clinical Rationale
This presentation is a medical red flag requiring urgent evaluation for diabetes mellitus. The International Children's Continence Society explicitly states that weight loss combined with polydipsia and enuresis indicates potential diabetes mellitus that must be ruled out immediately before considering primary enuresis. 1
Why Random Glucose is the Correct First Test
Immediate diagnostic capability: 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, 3
Symptoms indicate marked hyperglycemia: The American Diabetes Association guidelines specify that patients presenting with symptoms of marked hyperglycemia including polyuria, polydipsia, and weight loss should receive diagnostic testing for diabetes—this is not screening but rather diagnostic evaluation. 2
Time-sensitive diagnosis: Delaying glucose testing can lead to delayed diagnosis and prevention of diabetic complications, including progression to diabetic ketoacidosis. 1
Why Other Options Are Incorrect
A. Urine analysis and culture - While urine dipstick testing is appropriate in the evaluation algorithm, it is a secondary step. The International Children's Continence Society recommends immediate urine dipstick testing to detect glycosuria, but the presence of glycosuria then mandates immediate exclusion of diabetes mellitus with blood glucose testing. 1 Starting with urinalysis alone delays the critical diagnosis.
C. Refer to psychiatric - This would be a dangerous error. The American Academy of Pediatrics warns against dismissing the combination of weight loss, polydipsia, and enuresis as simple primary enuresis or psychogenic polydipsia, as this triad demands investigation for systemic disease. 1
D. Renal ultrasound - The International Children's Continence Society explicitly recommends against routine renal ultrasound in enuresis, as 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. 1 Ordering expensive imaging before basic screening tests wastes resources and delays diagnosis. 1
Expected Clinical Pathway
If random glucose ≥200 mg/dL with symptoms: Diabetes is diagnosed, and immediate treatment should be initiated. 2, 4
If random glucose is elevated but <200 mg/dL: Proceed with fasting plasma glucose or HbA1c for confirmation. 2, 4
If glucose testing is normal: Then proceed to urine dipstick for proteinuria (kidney disease), followed by electrolytes/renal function tests and frequency-volume chart to document polyuria. 1
Critical Pitfall to Avoid
The most dangerous error would be attributing these symptoms to primary nocturnal enuresis or psychogenic causes without first excluding diabetes mellitus. This patient requires blood glucose measurement as the immediate next step—any delay risks missing diabetic ketoacidosis or allowing preventable complications to develop. 1, 5