Most Appropriate Next Investigation
The most appropriate next investigation is immediate urine dipstick testing followed by blood glucose measurement (random plasma glucose or fingerstick glucose). 1, 2, 3
Clinical Rationale
This triad of bedwetting (nocturnal enuresis), weight loss, and polydipsia is a medical red flag that demands urgent evaluation for diabetes mellitus before considering any primary bladder disorder. 1, 2, 3 The International Children's Continence Society and American Academy of Pediatrics explicitly state that this combination indicates potential diabetes mellitus that must be ruled out immediately. 1, 3
Diagnostic Algorithm
Step 1: Immediate Urine Dipstick
- Perform urine dipstick testing first to detect glycosuria (glucose in urine) and proteinuria, which can indicate diabetes mellitus or kidney disease. 2, 3
- This is the fastest, most cost-effective screening test that can be done at point-of-care. 2
Step 2: Blood Glucose Testing
- If glycosuria is present on dipstick, immediately proceed with blood glucose testing (random plasma glucose or fingerstick glucose). 2, 3
- A random plasma glucose ≥200 mg/dL (11.1 mmol/L) in a patient with classic symptoms (polyuria/polydipsia and unexplained weight loss) is sufficient to diagnose diabetes mellitus without requiring fasting or additional testing. 1, 4
- If random glucose is elevated but <200 mg/dL, proceed with fasting plasma glucose or HbA1c for confirmation. 1
Step 3: Additional Testing Based on Initial Results
- Obtain HbA1c, electrolytes, and renal function tests to assess disease severity and screen for kidney disease. 2
- If proteinuria is present on repeat urine samples, initiate investigations for kidney disease. 3
- Consider a frequency-volume chart for 2-3 days to document polyuria and quantify fluid intake. 3
Critical Pitfalls to Avoid
Do not delay urine and glucose testing, as this can lead to delayed diagnosis and progression to diabetic ketoacidosis—a life-threatening complication. 2, 3 The American Diabetes Association specifies that patients presenting with symptoms of marked hyperglycemia including polyuria, polydipsia, and weight loss require diagnostic testing for diabetes, not screening. 1
Do not order renal ultrasound or other expensive imaging before basic screening tests, as this wastes resources and delays diagnosis. 2, 3 The International Children's Continence Society explicitly recommends against routine renal ultrasound in enuresis—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, 3
Do not dismiss this presentation as simple primary enuresis or psychogenic polydipsia without first ruling out systemic disease. 1, 2, 3 This is a common and dangerous error that can result in preventable morbidity and mortality.
Management if Diabetes is Confirmed
If the patient presents with marked hyperglycemia (blood glucose ≥250 mg/dL, A1C ≥8.5%) and is symptomatic with polyuria, polydipsia, nocturia, and/or weight loss, initial treatment should include basal insulin while metformin is initiated and titrated. 5 If ketosis or ketoacidosis is present, treatment with subcutaneous or intravenous insulin should be initiated immediately to rapidly correct the hyperglycemia and metabolic derangement. 5