What diagnostic labs would you run for a 16-year-old with recurrent illnesses?

Diagnostic Labs for a 16-Year-Old with Recurrent Illnesses

For a 16-year-old with recurrent illnesses, a comprehensive laboratory workup should include a complete blood count with differential, comprehensive metabolic panel, thyroid function tests, and vitamin B12 levels as the initial investigations. 1

Initial Laboratory Evaluation

• Complete Blood Count (CBC) with differential

  • Evaluates for anemia, leukopenia, leukocytosis, thrombocytopenia, or abnormal cell morphology
  • Helps identify infections, bone marrow disorders, and certain immunodeficiencies

• Comprehensive Metabolic Panel (CMP)

  • Includes electrolytes, liver function tests, kidney function tests, glucose
  • Add uric acid and lactate dehydrogenase (LDH) to assess for metabolic disorders 2

• Thyroid Function Tests

  • TSH and free T4 to evaluate for hypo/hyperthyroidism which can present with fatigue and recurrent illness 1

• Vitamin B12 Level

  • Deficiency can present with neurological symptoms and fatigue before anemia develops 1

Additional First-Line Testing

• Inflammatory Markers

  • Erythrocyte sedimentation rate (ESR)
  • C-reactive protein (CRP)
  • These help identify inflammatory or autoimmune processes 1

• Iron Studies

  • Ferritin, iron, TIBC, transferrin saturation
  • Particularly important in adolescents with fatigue 1

• Immunoglobulin Levels

  • IgG, IgA, IgM, IgE
  • Evaluates for immunodeficiency or allergic conditions 2

• Serum Tryptase

  • May be elevated in myeloproliferative disorders 2

Infection-Specific Testing

• Epstein-Barr Virus (EBV) Serology

  • Anti-viral capsid antigen (VCA) and anti-early antigen (EA) antibodies
  • Important in adolescents with persistent fatigue, lymphadenopathy 3

• Stool Studies

  • Ova and parasites test
  • Gastrointestinal PCR for pathogens if GI symptoms are present 2

• Serology for Strongyloides and other parasitic infections if travel history or exposure risk 2

Specialized Testing Based on Clinical Presentation

• Autoimmune Evaluation

  • Antinuclear antibodies (ANA)
  • Antineutrophil cytoplasmic antibodies (ANCA) 2

• Metabolic Screening

  • Urine organic acid profile if metabolic disorder suspected
  • Particularly important if encephalopathy occurs during illnesses 4

• Genetic Testing

  • Consider chromosomal microarray analysis if developmental issues or dysmorphic features present 1
  • Targeted genetic testing for specific metabolic disorders if clinically indicated 4

Imaging Studies

• Chest Radiograph

  • Baseline evaluation for recurrent respiratory infections 2

• Spirometry (pre- and post-β2 agonist)

  • Especially if respiratory symptoms are present 2

Red Flags Requiring More Extensive Evaluation

• Loss of developmental milestones or regression of skills
• Respiratory symptoms with generalized weakness
• Rapidly progressive weakness
• Recurrent severe infections with the same organism
• Family history of immunodeficiency 1, 5

Important Considerations

• Timing of laboratory evaluation is critical - ideally during acute illness episodes and during well periods for comparison
• Document patterns of illness (frequency, duration, associated symptoms)
• Consider bone marrow evaluation if blood count abnormalities persist
• Evaluate for periodic fever syndromes if fever pattern is recurrent 6

If initial evaluation is unrevealing but symptoms persist, consider referral to appropriate subspecialists (infectious disease, immunology, rheumatology) for further specialized testing and management.