In a pediatric patient, when should lead blood level testing and Quantiferon‑TB Gold testing be performed, and what are the recommended follow‑up actions for abnormal results?

Lead and QuantiFERON Testing in Pediatric Patients

Lead Blood Level Testing

All children should undergo lead screening at 12-24 months of age if they live in high-risk areas (≥25% housing built before 1960 or ≥5% prevalence of blood lead ≥5 μg/dL), have identified lead hazards in their home/childcare facility, or are immigrant/refugee/internationally adopted children upon arrival to the United States 1.

When to Test for Lead

• Age 12-24 months: Targeted screening for children in communities with ≥25% housing built before 1960 or prevalence of elevated blood lead ≥5% 1
• Any age: Test if living in or regularly visiting homes built before 1960 that are poorly maintained or recently renovated (past 6 months) 1
• Upon arrival: All immigrant, refugee, and internationally adopted children 1
• High-risk infants: Consider retesting at 3-6 months for children initially screened before 12 months of age as mobility increases 1

Follow-Up Actions Based on Results

The AAP adopted the CDC reference value of ≥5 μg/dL (≥50 ppb) for case management 1:

Blood Lead <5 μg/dL

• Review results with family (normal mean for US children 1-5 years is <2 μg/dL) 1
• Repeat in 6-12 months if high-risk exposure continues 1
• Provide anticipatory guidance about lead sources (pre-1960 paint, soil near roadways, imported spices/cosmetics/folk remedies) 1
• Assess nutrition and iron deficiency risk 1

Blood Lead 5-14 μg/dL

• Retest venous sample within 1-3 months to verify level is not rising 1
• Report to state health department (required in most states) 1
• Take detailed environmental history and provide exposure reduction advice 1
• Nutritional counseling for calcium and iron; encourage iron-enriched foods 1
• Screen for iron deficiency (CBC, ferritin, C-reactive protein) and treat per AAP guidelines 1
• Consider multivitamin with iron 1
• Perform structured developmental screening at all visits 1

Blood Lead 15-44 μg/dL

• Confirm with repeat venous sample within 1-4 weeks 1
• All above interventions plus:
• Consider abdominal radiography if history of pica or excessive mouthing 1
• Consult pediatric environmental health specialty unit (www.pehsu.net or 888-347-2632) 1

Blood Lead >44 μg/dL

• Confirm with repeat venous sample within 48 hours 1
• Consider hospitalization or chelation therapy with experienced provider 1
• Contact regional poison control center or CDC for assistance 1

Critical pitfall: Laboratory error can be ±4 μg/dL for levels ≤20 μg/dL, potentially causing misclassification 1. Always confirm elevated capillary samples with venous testing.

---

QuantiFERON-TB Gold Testing

QuantiFERON testing can be used in children ≥5 years as an alternative to TST, but exercise caution in children <5 years due to higher rates of indeterminate results and increased risk of progression to severe TB disease 2.

When to Use QuantiFERON

The 2010 CDC guidelines note that IGRAs (including QuantiFERON) may be used in place of TST in all situations where TST is recommended, but with important age-related considerations 2:

• Children ≥5 years: Less caution required; logistically easier (sufficient blood draw) and performance similar to adults 2
• Children <5 years: Use with caution due to:
  • Higher progression rates to active TB and severe disease (meningitis, disseminated disease, death) 2
  • Higher rates of indeterminate results (0-17% range across studies) 2
  • Age-related immunologic differences affecting test sensitivity 2
  • Lower IFN-γ production in response to antigens in some studies 2

Interpreting Results in Children

Important considerations:

• Agreement between TST and QuantiFERON is moderate (90.72%, Kappa 0.59) in children <5 years 3
• In non-BCG-vaccinated children, agreement improves substantially (95%, Kappa 0.75) 3
• Discordant TST+/QFT- results occur in 6% of cases 3
• For discordant QFT-/TST+ results in young children, treat as false negative QFT given high risk of progression to active disease 3
• All children with active TB disease had QFT values >4.00 IU/mL 3

Indeterminate Results

Indeterminate results are uncommon (0.46%) in nonimmunosuppressed children but may occur with 4:

• Acute bacterial infections with fever
• Concurrent β-lactam antibiotic therapy
• Asthma exacerbations on inhaled corticosteroids

Repeat testing after resolution of acute illness to avoid unnecessary repeat blood draws and costs 4.

Special Populations

• Immunosuppressed children: Hydroxychloroquine and steroids may decrease mitogen-induced IFN-γ, potentially affecting test interpretation 5
• HIV-positive patients: QuantiFERON positivity rate is 15.2%, lower than in chronic inflammatory disease patients (22.6%) 6

The most prudent approach for children <5 years is to consider both TST and QuantiFERON results together, treating any positive result as indication for preventive therapy given the high stakes of missed latent TB in this age group 2, 3.