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Etiology of diarrhea may be infectious or non-infectious presenting with acute (<7 days) or chronic (>7 days) symptoms. Parasites are an infrequent or rare cause of acute diarrhea but a more common cause of chronic diarrhea.
Tests generally appear in the order most useful for common clinical situations
| Test name: Giardia Antigen by EIA |
| ARUP #: 0060048 |
| Methodology: Qualitative Enzyme Immunoassay |
| Use: Diagnose Giardia duodenalis(synonyms Giardia lamblia, Giardia intestinalis) as etiology of diarrheal disease First-line test for suspected parasitic diarrhea; rapid (24-hour) turnaround Most sensitive method for detection of Giardia |
| Limitations: Will not detect parasites other than G. duodenalis Testing of second specimen may be indicated if first specimen is negative and clinical suspicion is high |
| Test name: Cryptosporidium Antigen by EIA |
| ARUP #: 0060045 |
| Methodology: Qualitative Enzyme Immunoassay |
| Use: Diagnose Cryptosporidium as etiology of diarrheal disease First-line test for suspected parasitic diarrhea; rapid (24-hour) turnaround Most sensitive test for detection of Cryptosporidium spp |
| Limitations: Will not detect parasites other than Cryptosporidium spp |
| Test name: Entamoeba histolytica Antigen, EIA |
| ARUP #: 0058001 |
| Methodology: Qualitative Enzyme Immunoassay |
| Use: Diagnose Entamoeba as etiology of diarrheal disease Order only for patients with risk factors for infection (eg, foreign travel) Specific and sensitive test for detection of intestinal E. histolytica |
| Limitations: Rarely positive in extraintestinal disease Will not detect parasites other than E. histolytica |
| Test name: Entamoeba histolytica (amebiasis), Antibody, IgG |
| ARUP #: 0050070 |
| Methodology: Semi-Quantitative Enzyme-Linked Immunosorbent Assay |
| Use: Confirm past infection Diagnose invasive extraintestinal disease |
| Limitations: Preferred test for extraintestinal disease (eg, liver abscess) |
| Test name: Parasitology Stain by Modified Acid-Fast |
| ARUP #: 0060046 |
| Methodology: Qualitative Concentration/Modified Acid-Fast Stain |
| Use: Detect Cryptosporidium, Cyclospora and Cystoisospora |
| Limitations: Not intended for detection of other stool parasites Less sensitive than EIA for Cryptosporidium spp |
| Test name: Microsporidia Stain by Modified Trichrome |
| ARUP #: 0060050 |
| Methodology: Qualitative Modified Trichrome Stain |
| Use: Detect microsporidia |
| Limitations: Not intended for detection of other stool parasites |
| Test name: Microsporidia DFA |
| ARUP #: 2003111 |
| Methodology: Direct Fluorescent Antibody Stain |
| Use: Detects and differentiates Encephalitozoon spp and Enterocytozoon bieneusi |
| Test name: Strongyloides Antibody, IgG by ELISA, Serum |
| ARUP #: 0099564 |
| Methodology: Semi-Quantitative Enzyme-Linked Immunosorbent Assay |
| Use: Confirm clinical suspicion of Strongyloides infection |
| Limitations: Most sensitive test in chronic infections |
| Follow-up: Antibody cross-reactions in patients with filariasis may occur |
| Test name: CBC with Platelet Count & Automated Differential |
| ARUP #: 0040003 |
| Methodology: Automated Cell Count with Flow Cell Differential |
| Use: Mild to moderate eosinophilia may suggest Strongyloides infection if stools are negative |
| Test name: Giardia lamblia Antibody by IFA |
| ARUP #: 0099439 |
| Methodology: Immunofluorescence Assay (Indirect Fluorescent Antibody) |
| Use: Diagnose Giardia duodenalis(synonyms Giardia lamblia, Giardia intestinalis) as etiology of chronic diarrhea after 1-2 weeks of disease First-line test for suspected parasitic diarrhea; rapid (24-hour) turnaround Includes IgG, IgA and IgM |
| Limitations: Insensitive relative to stool EIA |
| Test name: Ova & Parasite Exam, Fecal (Immunocompromised or Travel History) |
| ARUP #: 2002272 |
| Methodology: Qualitative Concentration Technique/Trichrome Stain/Microscopic Evaluation |
| Use: Diagnose most parasites (eg, Taenia spp Strongyloides, Giardia duodenalis, Entamoeba) as etiology of diarrheal disease in patient with defined risk factor or a high pre-test probability for parasitic infection |
| Limitations: Requires examination of 3 stool samples collected over 10 days to improve sensitivity Stool antigen testing is the optimal test method for determining the parasitic presence of Giardia duodenalis, Cryptosporidium spp, or Entamoeba histolytica Ova and parasite exam does not specifically detect Cryptosporidium, Cyclospora, Isospora, and Microsporidia For Cryptosporidium, refer to the Cryptosporidium Antigen by EIA test; for Cyclospora and Isospora, refer to Parasitology Stain by Modified Acid-Fast; for Microsporidia, refer to Microsporidia Stain |