What labs and diagnostic tests are commonly needed in a Peds (Pediatrics) ER (Emergency Room) clinical rotation and what diagnoses might they suggest?

Essential Labs and Diagnostic Tests in Pediatric ER Rotation

Core Laboratory Tests and Associated Diagnoses

The most essential laboratory tests for a Pediatric ER rotation include CBC with differential, basic metabolic panel, urinalysis, and targeted testing based on presenting symptoms rather than routine extensive panels. 1, 2

Baseline Tests and Common Indications

Blood Tests

• Complete Blood Count (CBC)

  • Suspected infection/sepsis
  • Unexplained fever
  • Bleeding disorders
  • Anemia
  • Malignancy evaluation

• Basic Metabolic Panel (BMP)/Comprehensive Metabolic Panel (CMP)

  • Dehydration assessment
  • Electrolyte abnormalities
  • Acid-base disturbances
  • Renal function evaluation
  • Diabetic ketoacidosis

• Liver Function Tests

  • Suspected hepatitis
  • Drug toxicity
  • Abdominal pain with jaundice
  • Medication monitoring

• Blood Cultures

  • Suspected bacteremia/sepsis
  • Fever without source in infants
  • Immunocompromised patients with fever
  • Note: Adequate blood volume is critical - age-appropriate filling increases pathogen detection threefold 3

Urine Tests

• Urinalysis

  • Suspected urinary tract infection
  • Abdominal/flank pain
  • Fever without source in young children
  • Note: Sensitivity for UTI using leukocyte esterase or nitrite is 88%, specificity 79% 1

• Urine Culture

  • Positive urinalysis findings
  • Recurrent UTI symptoms
  • Complicated UTI presentations
  • Note: Clean catch has 26% contamination rate vs. 12% for catheter specimens 1

• Urine Toxicology Screen

  • Altered mental status
  • Unexplained neurological symptoms
  • Suspected ingestion/overdose
  • Note: Routine screening has limited utility; only 5% positive in asymptomatic patients 1

Condition-Specific Testing Algorithms

Fever Evaluation

1. Infants 0-2 months with fever ≥38°C

   • CBC with differential
   • Blood culture
   • Urinalysis and urine culture
   • CSF analysis if ill-appearing

2. Children 2-24 months with fever ≥38°C

   • Urinalysis for all females and uncircumcised males <12 months
   • Consider chest X-ray with cough, hypoxia, rales, or fever ≥39°C 1
   • Blood work based on clinical appearance and risk factors

Mental Health/Behavioral Presentations

1. Initial evaluation

   • Targeted testing based on history and physical exam
   • Avoid routine extensive testing (false positives 8x more common than true positives) 2

2. Recommended tests when medical cause suspected:

   • BMP/CMP
   • CBC
   • Thyroid function (TSH, free T4)
   • Urinalysis
   • Toxicology screen if substance use suspected 2

3. Additional testing for specific presentations:

   • Disorientation/confusion: Consider neuroimaging
   • First-episode psychosis: More comprehensive evaluation
   • Abnormal vital signs: More extensive workup 1, 2

Respiratory Distress

1. Initial assessment

   • Pulse oximetry
   • Blood gas (arterial or venous) for moderate-severe distress
   • Chest X-ray for suspected pneumonia, foreign body, or structural abnormality

2. Additional testing based on presentation:

   • Respiratory viral panel during seasonal outbreaks
   • D-dimer and chest CT if pulmonary embolism suspected 1

Abdominal Pain

1. Initial evaluation

   • CBC with differential
   • CMP
   • Urinalysis
   • Pregnancy test for females of childbearing age

2. Additional testing based on presentation:

   • Lipase/amylase for suspected pancreatitis
   • Liver function tests for RUQ pain
   • Abdominal imaging based on clinical findings

Special Considerations

Age-Specific Testing Recommendations

• Neonates (0-28 days)

  • Lower threshold for full sepsis evaluation
  • Consider metabolic screening for unexplained symptoms

• Infants (1-12 months)

  • Urinalysis and culture for fever evaluation
  • Consider parechovirus PCR in CSF for infants <3 months 1

• Children (1-12 years)

  • More selective testing based on symptoms
  • Consider Mycoplasma testing for persistent respiratory symptoms

• Adolescents (13-18 years)

  • Include pregnancy testing for females
  • Consider expanded toxicology testing
  • Screen for depression, anxiety, and suicidal ideation 1

Immunocompromised Patients

Require more extensive evaluation including:

• CMV PCR
• HHV6/7 PCR
• HIV testing
• Cryptococcal antigen
• Toxoplasma serology/PCR
• Fungal testing 1

Common Pitfalls to Avoid

1. Over-reliance on routine testing

   • Less than 1 in 50 routine tests yields clinically meaningful findings 2
   • Target testing based on history and physical exam

2. Inadequate blood culture volumes

   • Insufficient volume leads to missed pathogens and increased contamination
   • Follow age-appropriate volume guidelines 3

3. Misinterpreting urinalysis results

   • 30% of positive urine cultures may have negative urinalysis
   • Consider culture despite negative urinalysis in high-risk patients 1

4. Attributing symptoms to psychiatric causes without adequate medical workup

   • Always consider medical causes of behavioral symptoms
   • Abnormal vital signs warrant more extensive evaluation 1, 2

5. Delaying treatment with excessive testing

   • Balance diagnostic thoroughness with timely intervention
   • Consider empiric treatment while awaiting results in high-risk scenarios

By following these evidence-based guidelines for laboratory and diagnostic testing in the Pediatric ER, you can efficiently identify important medical conditions while avoiding unnecessary testing and delays in care.