Laboratory Workup for Persistent Vomiting in a 1-Year-Old
The laboratory workup for persistent vomiting in a 1-year-old should be guided by clinical presentation and red flag signs, with basic metabolic panel, electrolytes, and blood gas analysis being the core initial tests when dehydration or concerning features are present. 1
Initial Clinical Assessment Determines Laboratory Testing
The decision to pursue laboratory testing depends critically on the presence of red flag signs and hydration status, rather than routine screening in all vomiting children. 1, 2
Red Flag Signs Requiring Laboratory Evaluation
Laboratory investigations are indicated when any of the following are present: 1, 2
- Bilious or bloody vomiting - suggests obstruction or surgical pathology
- Signs of dehydration - decreased urine output (fewer than 4 wet diapers in 24 hours), poor skin turgor, altered mental status
- Altered sensorium or toxic appearance
- Severe wasting or poor weight gain
- Concern for metabolic abnormalities - lethargy, acidotic breathing pattern
Core Laboratory Tests
Essential Initial Laboratory Panel
When laboratory evaluation is warranted, obtain: 1, 3
- Serum electrolytes (sodium, potassium, chloride, bicarbonate) - to assess for dehydration severity and electrolyte imbalances
- Blood gas analysis - to identify metabolic acidosis from dehydration or underlying metabolic disorders
- Blood glucose - to exclude symptomatic hypoglycemia, particularly concerning in infants
- Renal function tests (BUN, creatinine) - to assess degree of dehydration and kidney function
- Complete blood count - to evaluate for infection or anemia
Additional Testing Based on Clinical Suspicion
Expand laboratory workup when specific conditions are suspected: 1, 3
- Liver function tests - if hepatobiliary disease suspected
- Amylase and lipase - if pancreatitis considered
- Urinalysis and urine culture - urinary tract infection is a common extraintestinal cause of vomiting in infants
- Thyroid-stimulating hormone - if endocrine disorder suspected
- Metabolic screening - if inborn error of metabolism suspected (particularly with altered mental status or family history)
Important Clinical Context
When Laboratory Testing May NOT Be Necessary
In an otherwise healthy 1-year-old with nonbilious vomiting, normal hydration status, appropriate weight gain, and no red flag signs, laboratory testing is often unnecessary. 4, 2 The most common causes in this scenario are viral gastroenteritis or gastroesophageal reflux, which are clinical diagnoses. 5, 2
Hydration Assessment Guides Laboratory Urgency
The Centers for Disease Control and Prevention framework for dehydration severity helps determine laboratory urgency: 6
- Mild dehydration (3-5% deficit) - may not require immediate laboratory testing if oral rehydration is tolerated
- Moderate dehydration (6-9% deficit) - laboratory evaluation recommended
- Severe dehydration (≥10% deficit) - urgent laboratory evaluation and IV fluid resuscitation required
Critical Pitfalls to Avoid
Do not delay imaging or surgical consultation while awaiting laboratory results if bilious vomiting is present. 4, 7 Bilious vomiting represents a surgical emergency until proven otherwise, particularly concerning for malrotation with volvulus, which can lead to intestinal necrosis within hours. Abdominal radiograph should be obtained immediately, with surgical consultation, regardless of laboratory values. 7
Do not perform routine laboratory screening in well-appearing infants with simple gastroesophageal reflux. 8 The yield is extremely low and does not change management in otherwise healthy infants with chronic nonbilious vomiting and normal growth. 8
Recognize that normal laboratory values do not exclude serious pathology. 1 Surgical causes of vomiting (pyloric stenosis, intussusception, malrotation) require imaging studies, not laboratory diagnosis. 4, 6