What laboratory studies should be ordered to evaluate a patient with pica?

Laboratory Assessment for Pica

Order a complete blood count (CBC) with iron studies (serum iron, ferritin, and C-reactive protein) as the primary laboratory evaluation for any patient presenting with pica. 1, 2

Essential Laboratory Tests

Iron Status Assessment (First Priority)

• CBC with differential to evaluate for anemia 1
• Serum ferritin to assess iron stores 1
• C-reactive protein (CRP) to interpret ferritin accurately, as ferritin is an acute phase reactant 1
• Serum iron and total iron-binding capacity for comprehensive iron status evaluation 3, 4

The relationship between pica and iron deficiency is substantial—patients with pica have 2.35 times greater odds of anemia and significantly lower hemoglobin (-0.65 g/dL), hematocrit (-1.15%), and zinc concentrations (-34.3 μg/dL) compared to controls 2. This association persists across all pica subtypes (geophagia, amylophagia, pagophagia) and life stages 2.

Additional Micronutrient Testing

• Plasma zinc concentration should be measured, as pica is associated with significantly lower zinc levels 2
• Comprehensive metabolic panel to assess overall nutritional status and identify complications 1

Lead Exposure Screening (Critical in Specific Contexts)

When to Test for Lead

• Children with pica behavior require blood lead testing, particularly those with history of paint chip ingestion or excessive mouthing behaviors 1
• Venous blood lead measurement is the gold standard and must be used for diagnostic purposes 5, 6
• Capillary (fingerstick) samples are prone to contamination and should only be used for initial screening, with any elevated result confirmed by venous sampling 5, 6

Lead Testing Specifications

• Use laboratories designated by OSHA that meet specific proficiency requirements 5
• Select laboratories achieving routine performance within ±2 μg/dL rather than the federally permitted ±4 μg/dL 5, 6
• Testing should use inductively coupled plasma-mass spectrometry (ICP-MS) 5

Heavy Metal Panel (When Clinically Indicated)

For patients with specific exposures or neurological symptoms:

• Blood analysis for lead, cadmium, and mercury 5
• 24-hour urine collection or spot urine for arsenic, cadmium, copper, lead, mercury, and zinc 5
• Hair and nail analysis reflects past exposure rather than current levels and has limited clinical utility 5

Imaging Studies for Complications

Abdominal Radiography

• Consider abdominal X-ray for children with history of paint chip pica or excessive mouthing behaviors to identify leaded foreign bodies 1
• Standard abdominal X-ray is essential for patients with gastrointestinal symptoms, as anamnesis is often difficult in patients with mental disorders and pica has high incidence of surgical complications 7

Clinical Context and Pitfalls

Common Diagnostic Errors to Avoid

• Do not assume pica will resolve with iron supplementation alone—only a minority of patients show improvement after iron correction 7
• Do not overlook psychiatric comorbidities—87% of patients with pica have associated psychiatric disorders including severe mental impairment, dysharmonic development, autistic disorders, or schizophrenia 7
• Do not delay testing based on symptom severity—patients can present with critically low hemoglobin (as low as 1.6 g/dL) yet remain ambulatory 4

Interpretation Considerations

• Laboratory variability at low blood lead levels can be ±2-3 μg/dL, so serial measurements help establish true trends 6
• Ferritin must be interpreted alongside CRP, as inflammation falsely elevates ferritin levels 1
• The absence of anemia does not exclude clinically significant pica, as the behavior may precede measurable deficiencies 2

Special Populations

• Pregnant women require particular attention to iron studies, as pica is common during pregnancy and associated with increased micronutrient demands 8
• Children ages 1-2 years with pica should undergo risk-based lead screening regardless of other symptoms 9
• Patients with developmental disorders or autism spectrum disorder warrant comprehensive evaluation, as pica is strongly associated with these conditions 8