What is the diagnosis for a 9-year-old boy presenting with abdominal pain, bloating, vomiting, and diarrhea, with a white blood cell (WBC) count of 16, indicating leukocytosis, and no high-grade fever?

Acute Gastroenteritis with Leukocytosis

This 9-year-old boy most likely has acute viral gastroenteritis, with the elevated WBC count of 16,000/µL representing a physiologic stress response rather than bacterial infection. 1, 2

Primary Diagnosis: Viral Gastroenteritis

The clinical presentation strongly supports viral gastroenteritis based on:

• Classic symptom triad: Abdominal pain, vomiting (2 episodes), and diarrhea (3 episodes) without high-grade fever is typical of viral etiology 1, 3
• Age-appropriate epidemiology: Rotavirus and other viral pathogens account for approximately 25% of acute diarrhea cases in children under 5 years, with similar patterns extending through school age 1
• Leukocytosis pattern: A WBC of 16,000/µL with presumed neutrophilia is common in viral gastroenteritis as a stress response and does not necessarily indicate bacterial infection 2

Critical Differential Considerations

When to Suspect Bacterial Infection

You should reconsider bacterial etiology if any of these develop:

• Bloody or mucoid stools suggesting Salmonella, Shigella, Campylobacter, or STEC 1, 2
• Extreme leukocytosis (leukemoid reaction) which may indicate Shigella 2
• Progressive clinical deterioration despite appropriate hydration 1
• Persistent high fever (>39°C for >48 hours) with signs of sepsis 1

Appendicitis Must Be Excluded

Given the elevated WBC and abdominal pain:

• High WBC with left shift has 80% sensitivity and 79% specificity for appendicitis in children aged 4-12 years 4
• Key discriminating features: Localized right lower quadrant tenderness, rebound tenderness, guarding, or decreased bowel sounds would favor appendicitis over gastroenteritis 4, 5
• If left shift is present on differential: 54.3% of children with left shift have appendicitis vs. 5.4% without left shift (NPV 90.5%) 4

Immediate Management Algorithm

Step 1: Assess Dehydration Status

Evaluate using these clinical parameters 1, 3:

• Skin turgor, capillary refill, mucous membrane moisture are the most reliable predictors 6
• Categorize severity: Mild (3-5% deficit), moderate (6-9%), or severe (≥10%) 1, 3
• Abnormal capillary refill, abnormal skin turgor, and abnormal respiratory pattern are the three most useful predictors of ≥5% dehydration 6

Step 2: Initiate Oral Rehydration Immediately

Do not wait for diagnostic testing 1, 3:

• Administer 50 mL/kg ORS over 2-4 hours for mild-moderate dehydration 1
• Use low-osmolarity ORS formulations, not sports drinks or juices 3
• Continue age-appropriate feeding during and immediately after rehydration 1, 3

Step 3: Consider Ondansetron for Persistent Vomiting

If vomiting interferes with oral rehydration 3, 6:

• Ondansetron may be given to children >4 years to facilitate oral rehydration 3
• Evidence shows: Decreased vomiting rate, improved oral intake, reduced need for IV hydration, and shorter ED stay 6
• Very few serious side effects have been reported 6

Step 4: Avoid Harmful Interventions

Critical pitfalls to avoid 1, 3:

• Never use antimotility agents (loperamide) in children—can cause ileus and death 1, 3
• Do not prescribe antibiotics for viral gastroenteritis—no benefit and potential harm 1, 3
• Avoid high-sugar fluids (soft drinks, undiluted apple juice)—exacerbate diarrhea through osmotic effects 3

When to Hospitalize

Admit if any of the following are present 1:

• Severe dehydration requiring IV fluids
• Inability to tolerate oral fluids despite ORS attempts
• Altered mental status or signs of shock
• Persistent high fever with signs of sepsis

Laboratory Testing Considerations

Routine laboratory testing is not necessary for typical viral gastroenteritis 2:

• WBC count alone does not accurately predict dehydration severity 6
• Consider stool studies only if: Bloody diarrhea, recent antibiotic use, recent foreign travel, or immunodeficiency 3
• Monitor for HUS if STEC suspected: Serial hemoglobin, platelet count, electrolytes, BUN, and creatinine 2

Common Clinical Pitfall

The elevated WBC of 16,000/µL in this case is likely a physiologic stress response to dehydration and viral illness, not bacterial infection 2. However, you must obtain a WBC differential to assess for left shift, which would significantly increase the probability of appendicitis and warrant surgical consultation 4. The absence of high-grade fever and the presence of diarrhea make viral gastroenteritis far more likely than appendicitis, but the combination of abdominal pain, bloating, and leukocytosis mandates careful serial abdominal examinations 4, 5.