Dientamoeba Fragilis Infection Workup
- Author: David R Mack, MD, FRCPC; Chief Editor: Russell W Steele, MD more...
Blood test results are usually normal in patients with Dientamoeba fragilis infection. However, a CBC count with differential may reveal eosinophilia in as many as 50% of children infected with the parasite.
The usual method for confirming the diagnosis is examination of a permanently stained smear of fresh feces, preserved immediately, for the morphologic characteristics of D fragilis trophozoites. Newer, but experimental, techniques include immunofluorescence and real-time polymerase chain reaction (PCR) techniques. Culture is not routinely available.
Preferred stool preparation involves a fresh sample that is immediately preserved with polyvinyl alcohol fixative, sodium acetate-acetic acid-formalin fixative, or Schaudinn fixative. Immediate preservation is necessary because, in unpreserved feces, the morphologic characteristics of the trophozoites do not persist, and they round up and become granular within 15 minutes at room temperature.
A single sample is diagnostic only 50-60% of the time. Three separate samples increase the yield to 70-85%, and 6 separate samples increase the yield to 90-95%.
Ensure that stool samples are collected on alternate days because D fragilis can be excreted in a cyclic pattern similar to G lamblia. The final portion of the stool evacuation may contain the most concentrated numbers of trophozoites. Collect stool specimens before radiologic procedures that use barium because barium interferes with trophozoite detection and may do so for several weeks.
Other medications that can interfere with parasite detection include antibiotics, antiprotozoan medication, antimalarials, mineral oil, bismuth-containing preparations, and nonabsorbable diarrheal medications. Process stool specimens in the laboratory with the formalin-ether sedimentation concentration technique and stain with either iron hematoxylin, trichrome, or celestin B.
Diagnostic characteristics are a pleomorphic trophozoite ranging in diameter from 5-15 mm (range, 4-30 mm) that contains 1-4 nuclei. The most common form is binucleated. However, approximately 20-30% are uninucleated. Multinucleated forms also can be present. The nuclei are distinctive, with several (4-8) chromatin granules clumped in the center of each nucleus. The cytoplasm frequently contains numerous food vacuoles.
Radiologic test findings are usually normal.
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