Diagnostic Approach for Pediatric Acute Gastroenteritis
In most children with acute gastroenteritis, laboratory testing is unnecessary and should not delay rehydration therapy. 1 The diagnosis is primarily clinical, based on history and physical examination findings.
Clinical Assessment (Required for All Patients)
Obtain an accurate body weight to guide fluid replacement calculations and serve as the most reliable measure of dehydration severity. 1
Essential History Elements
- Recent fluid intake and output patterns - significant dehydration is unlikely if parents report no decrease in oral intake or urine output and no vomiting 2
- Stool characteristics - frequency, consistency, presence of blood or mucus 1
- Associated symptoms - fever, vomiting duration and frequency 1
- Exposure history - recent antibiotic use (suspect Clostridium difficile), daycare attendance (consider Giardia or Shigella), recent foreign travel, or immunodeficiency 1
Physical Examination Findings
Focus on clinical signs that best predict dehydration severity: 3
- Skin turgor and capillary refill time (>2 seconds suggests significant dehydration) 1
- Respiratory pattern (rapid, deep breathing indicates acidosis) 1, 3
- Mental status (lethargy or altered consciousness) 1
- Mucous membrane moisture 1, 4
- Perfusion status (cool extremities, decreased capillary refill) 1
- Bowel sounds before initiating oral therapy 1
- Visual stool examination to confirm consistency and identify blood or mucus 1
Categorize dehydration severity: 1, 5
- Mild (3-5%): increased thirst, slightly dry mucous membranes
- Moderate (6-9%): loss of skin turgor, skin tenting, dry mucous membranes
- Severe (≥10%): severe lethargy, prolonged skin tenting, cool/poorly perfused extremities, signs of shock
Laboratory Testing (Selective Use Only)
Serum Electrolytes
Measure serum electrolytes only when: 1, 3
- Clinical signs suggest abnormal sodium or potassium concentrations 1
- Severe dehydration is present (≥10% fluid deficit) 3
- Intravenous rehydration is being considered 6
Do not routinely obtain electrolytes in mild to moderate dehydration - they are unnecessary and delay appropriate rehydration therapy. 3
Stool Studies
Obtain stool cultures when: 1
- Bloody diarrhea (dysentery) is present - this is the primary indication 1
- White blood cells visible on methylene blue stain of stool 1
- Persistent diarrhea despite appropriate management 3
- Unusual pathogen suspected (E. coli O157:H7, Cryptosporidium) 6
- Immunocompromised patient 1
Do not obtain stool cultures for: 2
- Typical viral gastroenteritis presentation (watery diarrhea, vomiting, child <2 years) 1
- Mild illness when viral etiology is likely 2
Common Pitfalls to Avoid
Do not delay rehydration while awaiting diagnostic test results - begin oral rehydration therapy immediately based on clinical assessment. 5 The most common error is over-testing children with straightforward viral gastroenteritis, which adds unnecessary cost and delays appropriate fluid therapy. 1
Do not routinely screen for non-gastrointestinal causes unless specific clinical features suggest alternative diagnoses such as meningitis, bacterial sepsis, pneumonia, otitis media, urinary tract infection, metabolic disorders, congestive heart failure, toxic ingestions, or trauma. 1 These conditions may present with fever, vomiting, and loose stools but require targeted evaluation based on clinical suspicion.