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Etiology of diarrhea may be infectious or non-infectious presenting with acute (<7 days) or chronic (>7 days) symptoms. Viral agents are the most common cause of diarrheal illness. Norovirus (Norwalk-like virus) and rotavirus are the two predominant viral agents. 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: CBC with Platelet Count & Automated Differential |
| ARUP #: 0040003 |
| Methodology: Automated Cell Count with Flow Cell Differential |
| Use: Nonspecific, but suggests bacterial etiology if leukocytosis is present |
| Limitations: Presence of anemia (low hemoglobin/hematocrit) suggestive of inflammatory or malignant process and not bacterial diarrhea |
| Test name: Stool Culture, Routine (Includes E. coli Shiga-like Toxin by EIA 0060047) |
| ARUP #: 0060134 |
| Methodology: Standard reference procedures for Salmonella, Shigella, Campylobacter, and E. coli 0157 culture and identification. |
| Use: First-line test for suspected bacterial diarrhea Cultures include Salmonella, Shigella, Campylobacter, and E. coli 0157 as well as EIA for Shiga-like toxin from E. coli |
| Test name: Norovirus Group 1 & 2 Detection by RT-PCR |
| ARUP #: 0051281 |
| Methodology: Qualitative Reverse Transcription Polymerase Chain Reaction |
| Use: Diagnose norovirus-associated gastroenteritis |
| Limitations: Negative result does not rule out the presence of PCR inhibitors (heme) in the patient specimen or norovirus nucleic acid concentrations below the level of detection of the assay Does not rule out presence of bacterial or other viral causes of gastroenteritis |
| Test name: Rotavirus Antigen by EIA |
| ARUP #: 0065088 |
| Methodology: Qualitative Enzyme Immunoassay |
| Use: Diagnose rotavirus-associated gastroenteritis |
| Limitations: Does not rule out presence of bacterial or other viral causes of gastroenteritis Negative result does not exclude the possibility of rotavirus infection Low virus quantity or improper/inadequate sampling can cause false-negative results |
| Test name: Rotavirus & Adenovirus 40-41 Antigens |
| ARUP #: 0065067 |
| Methodology: Qualitative Enzyme Immunoassay |
| Use: Diagnose rotavirus- and adenovirus-associated gastroenteritis |
| Limitations: Does not rule out presence of bacterial or other viral causes of gastroenteritis Negative result does not exclude the possibility of rotavirus infection Low virus quantity or improper/inadequate sampling can cause false-negative results Positive adenovirus results should be interpreted with caution since adenovirus is capable of latency and recrudescence Asymptomatic shedding may persist for months after infection False-positive adenovirus results can occur with high levels of Staphylococcus aureus expressing Protein A; however, staphylococcal enterocolitis is uncommon in adults and extremely rare in infants and children |
| 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, Giardia duodenalis, Entamoeba, Taenia spp, Strongyloides) 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 The 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 |