What blood work is recommended for a patient with failure to thrive (FTT)?

Recommended Blood Work for Failure to Thrive

For patients with failure to thrive (FTT), laboratory evaluation should include complete blood count, urinalysis, serum electrolytes (including calcium and magnesium), blood urea nitrogen, serum creatinine, glucose, lipid profile, liver function tests, iron studies, and thyroid-stimulating hormone to optimize management. 1

Core Laboratory Tests

The following laboratory tests should be ordered for all patients presenting with failure to thrive:

1. Complete blood count (CBC) - To assess for anemia, infection, or other hematologic abnormalities
2. Urinalysis - To screen for renal disease or infection
3. Comprehensive metabolic panel:
   • Serum electrolytes (sodium, potassium, calcium, magnesium)
   • Blood urea nitrogen (BUN)
   • Serum creatinine
   • Glucose
   • Liver function tests (ALT, AST, bilirubin)
4. Lipid profile - To assess nutritional status and metabolic health
5. Iron studies (serum iron, ferritin, transferrin saturation) - To evaluate for iron deficiency
6. Thyroid-stimulating hormone (TSH) - To rule out thyroid dysfunction

Additional Testing Based on Clinical Context

Depending on clinical suspicion, the following additional tests should be considered:

For Infants and Young Children

• Fecal elastase - To evaluate pancreatic function 1
• Sweat chloride test - If cystic fibrosis is suspected
• Celiac disease screening - Tissue transglutaminase antibodies
• Lead level - Particularly in children with environmental exposure risk

For Older Adults

• Vitamin B12 and folate levels - To assess for deficiencies common in elderly
• 25-hydroxyvitamin D level - To evaluate vitamin D status
• Inflammatory markers (ESR, CRP) - To screen for inflammatory conditions
• Albumin and prealbumin - To assess protein status and recent nutritional intake

Imaging and Additional Workup

• Chest X-ray - If respiratory symptoms are present
• Swallowing evaluation - For patients with suspected dysphagia or aspiration
• Gastroesophageal reflux evaluation - For symptomatic patients or those with unexplained FTT

Important Considerations

1. Laboratory testing should be targeted based on clinical findings rather than performed as an extensive battery of tests for all patients 2

2. For pediatric patients, routine laboratory evaluation with extensive testing yields an organic etiology in less than 1.4% of cases when there are no specific symptoms suggesting organic disease 2

3. In elderly patients with failure to thrive, medication review is essential as drug side effects or interactions may contribute to the condition 3

4. Reassessment of laboratory values should be performed with changes in clinical condition or treatments 1

5. For infants with chronic lung disease, additional monitoring of bone health markers may be warranted (calcium, phosphorus, alkaline phosphatase) 1

The laboratory evaluation should be part of a comprehensive assessment that includes detailed nutritional history, growth measurements, and evaluation for psychosocial factors that may contribute to failure to thrive.