A. Does patient have urinary frequency and urgency? Consider voiding dysfunction (most common diagnosis) and uTi.
B. Nocturnal enuresis or nocturia? Lack of nocturnal involvement usually excludes organic etiology.
C. Does patient drink excessively? Is there nocturnal polydipsia (patient awakened by thirst)? Drinking large amounts of fluid during the day often is a habit but may have an organic etiology.
D. Is there a history of GU problems? Conditions that may result in kidney damage and secondary polyuria include renal maldevelopment, posterior urethral valves, and pyelonephritis.
III. Differential Diagnosis
A. Urinary Frequency and Urgency
1. Voiding dysfunction.
2. Transitional voiding.
B. Excessive Drinking (Polydipsia)
1. Organic. High serum osmolarity; common presentation is a thirsty child. Renal conditions that prevent normal urinary concentrating ability and high solute loss (as in diabetes mellitus) may present with polyuria and polydipsia.
2. Behavioral (psychogenic or compulsive). Normal serum osmolarity; this presentation is unlikely in young children.
C. Diabetes Insipidus. Large volume of diluted urine.
1. Renal or nephrogenic. Kidney is insensitive to vasopressin.
a. Renal dysplasia (congenital maldevelopment).
b. Obstructive nephropathy.
c. Interstitial nephritis (pyelonephritis).
d. Renal insufficiency.
e. Renal tubular acidosis.
f. Sickle cell nephropathy.
2. Neurogenic (central). Loss of antidiuretic hormone (ADH) secretion secondary to tumor, trauma, or, rarely, iatrogenic causes.
D. Diabetes Mellitus. Polyphagia and glucosuria are evident.
A. Physical Exam Key Points
1. Assess general appearance.
2. Observe for signs of dehydration.
3. Measure body weight and BP
4. Exclude abdominal mass.
B. Laboratory Data
1. Metabolic panel. Obtain serum electrolytes, glucose, creatinine, and BUN.
2. Urinary evaluation. Urinalysis with specific gravity, urine culture, and serum osmolarity (urine specific gravity > 1.020 excludes a concentrating defect).
3. CBC. To exclude sickle cell disease, as clinically indicated.
C. Radiographic and Other Studies. Consider based on findings from history, physical exam, laboratory studies, and clinical course. Imaging of urinary tract will identify patients with renal maldevelopment or obstructive uropathy.
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