What initial blood tests are recommended for a 9-year-old with poor growth?

Initial Blood Tests for Poor Growth in a 9-Year-Old Child

A comprehensive panel of blood tests should be ordered for a 9-year-old with poor growth, focusing on thyroid function, celiac disease screening, complete blood count, and basic metabolic assessment to identify the most common underlying causes.

Core Initial Laboratory Evaluation

Essential First-Line Tests

• Complete Blood Count (CBC)

  • Screens for anemia, infection, and other hematologic abnormalities
  • Particularly important as anemia can be both a cause and consequence of poor growth 1

• Comprehensive Metabolic Panel

  • Electrolytes, BUN, creatinine (kidney function)
  • Liver function tests
  • Glucose (to rule out diabetes)
  • Calcium, phosphorus, alkaline phosphatase (bone metabolism)

• Thyroid Function Tests

  • TSH and free T4
  • Thyroid dysfunction is one of the most common endocrine causes of poor growth 2
  • Should be performed at initial evaluation of poor growth 2

• Celiac Disease Screening

  • IgA tissue transglutaminase antibodies (tTG) with total IgA levels
  • If IgA deficient, measure IgG tTG and deamidated gliadin peptide antibodies
  • Celiac disease is associated with poor growth and can present primarily as growth failure 2

Additional First-Line Tests

• Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP)

  • Inflammatory markers to screen for chronic inflammatory conditions

• Insulin-like Growth Factor 1 (IGF-1) and IGF Binding Protein 3 (IGFBP-3)

  • Screening tests for growth hormone deficiency
  • Growth hormone deficiency is rare but responds well to treatment 2

• 25-hydroxyvitamin D

  • To assess vitamin D status, which impacts bone health and growth 2

Considerations Based on Clinical Findings

If Specific Concerns Are Present

• Karyotype/Chromosomal Analysis

  • Consider if dysmorphic features are present
  • Important for identifying genetic disorders, which account for 20% of organic causes of poor growth 3

• Sweat Chloride Test

  • If respiratory symptoms or family history suggests cystic fibrosis

• Fecal Elastase

  • If symptoms suggest malabsorption or pancreatic insufficiency

Interpretation and Follow-Up

• Poor growth can be due to insufficient intake (59%), organic disease (20%), mechanical feeding difficulties (11%), or mixed/unknown causes (10%) 3
• Careful attention to growth measurements and plotting on appropriate growth charts is essential 4, 5
• Height velocity should be calculated and interpreted in context of the child's current height percentile 5
• Consider that 65% of organic diseases and only 39% of genetic disorders causing poor growth are diagnosed during initial evaluation 3

Important Caveats

• Ensure accurate height and weight measurements using calibrated equipment 5
• Consider parental heights when evaluating a child's growth pattern 2
• Poor growth may be the first sign of many systemic conditions, making laboratory screening crucial 4
• If initial screening is normal but growth continues to be poor, consider referral to pediatric endocrinology for more specialized testing
• Abnormal laboratory findings should prompt appropriate follow-up, as studies show these are often overlooked 6

Remember that early identification of the cause of poor growth allows for timely intervention, which is critical for optimizing growth potential and overall health outcomes.