Diagnosis: Folate Deficiency Anemia Secondary to Giardiasis
The most likely diagnosis is B. Giardiasis Parasitic Infection, which explains both the persistent diarrhea and the macrocytic anemia pattern seen in this child.
Clinical Reasoning
Laboratory Pattern Analysis
The lab findings show a macrocytic anemia (low Hgb, high MCV), which immediately narrows the differential diagnosis. The high MCHC is likely a laboratory artifact or measurement error, as true elevation of MCHC above physiologic limits (typically 35-36 g/dL) is rare and often represents interference 1, 2. The key finding is the high MCV indicating macrocytic anemia.
Why Giardiasis is the Answer
Giardia lamblia is the most common parasitic cause of persistent diarrhea lasting weeks to months 3, 4. This organism causes:
- Malabsorption syndrome leading to folate and vitamin B12 deficiency, which produces macrocytic anemia
- Chronic diarrhea that can persist for extended periods without treatment 4, 5
- Symptoms that may be mild or intermittent, consistent with a "fussy eater" who may have chronic low-grade symptoms 5
The goat milk consumption is a critical epidemiologic clue - unpasteurized or contaminated goat milk can be a source of Giardia cysts. Combined with being a fussy eater (suggesting poor nutritional intake that compounds malabsorption), this creates the perfect scenario for giardiasis with secondary nutritional deficiency 3, 4.
Why Other Options Don't Fit
A. Psychological Deprivation would not explain:
- The persistent diarrhea as a primary symptom
- The macrocytic anemia pattern (would more likely see microcytic anemia from iron deficiency if nutritional)
C. Aplastic Anemia presents with:
- Pancytopenia (low WBC, platelets, and RBC)
- Normocytic or slightly macrocytic anemia, but not with isolated macrocytosis and diarrhea
- No gastrointestinal symptoms as primary presentation
D. Hypothyroidism typically causes:
- Normocytic or mildly macrocytic anemia
- Constipation rather than diarrhea
- Other systemic symptoms (growth delay, cold intolerance, bradycardia)
Diagnostic Approach
For persistent diarrhea in children, parasitic testing should be performed 3. Specifically:
- Stool examination for ova and parasites with specific request for Giardia and Cryptosporidium testing, as routine O&P may not include these 3
- Giardia and Cryptosporidium testing is often performed together as the primary parasitology examination 3, 4
- Travelers or those with diarrhea lasting ≥14 days should be evaluated for intestinal parasitic infections 3
Critical Pitfall to Avoid
Do not assume routine stool O&P testing includes Giardia - clinicians must specifically request Cryptosporidium and/or Giardia testing 3. This is a common reason for missed diagnoses.
Management Implications
Once giardiasis is confirmed:
- Treatment with metronidazole, nitazoxanide, or albendazole 5
- Folate and B12 supplementation to correct the macrocytic anemia
- Nutritional counseling regarding safe milk consumption
- Reevaluation if symptoms persist, as some cases require combination therapy for eradication 5
The combination of persistent diarrhea, goat milk exposure, poor dietary intake, and macrocytic anemia creates a classic presentation for giardiasis with secondary malabsorption-induced folate deficiency.