Gastroenterology clinical image challenge: A 35-year-old man who had been in good health presented with several weeks of worsening abdominal pain, constipation, intermittent cramping, fatigue and nausea. He was an office worker and had traveled to India about two months prior. Clinical examination revealed a tender and slightly distended abdomen. Initial evaluation included complete blood count, electrolytes, urinalysis, celiac serology and liver function tests, which were all in normal range except for a normocytic anemia with a hemoglobin of 9.5 g/dL. A computed tomography scan, ultrasound examination of the abdomen and upper endoscopy with biopsy were also normal. An examination of blood smear revealed basophilic stippling of erythrocytes along with tear drop red cells (figure).
What is the next test to be ordered?
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