Diagnostic Utility of Ova and Parasite Testing in Hospitalized Patients

From the 2018 HVPAA National Conference

Jessica Barnes (University of Texas Southwestern Medical Center, Dallas, TX;), Kadam Patel (University of North Texas Health Sciences Center), Paul Southern (University of Texas Southwestern Medical Center, Dallas, TX;), Deepak Agrawal (University Texas Southwestern Medical Center)


Patients presenting to emergency room or admitted to the hospital with loose bowel movements are usually evaluated with multiple tests, including ova and parasite (O&P) stool testing. Prior studies have shown low yield for O&P, especially when checked greater than 3 days after admission.


To evaluate the diagnostic utility of stool O&P testing, at a large county hospital, and determine the most cost-effective utilization of the test.


Retrospective analysis of O&P stool studies performed on patients in the emergency room or as inpatients at a county hospital from December 2011 to February 2017. The frequency of positive results was evaluated. Subgroup analysis was performed based on timing of testing, greater or less than 72 hours since admission. Detailed chart review was performed for patients with positive O&P results to determine duration and severity of diarrhea, immunosuppressed state (HIV, malignancy, end stage renal disease, immunosuppressive disorders), co-infection with C-difficile and treatment.


Stool O&P was positive in 112 out of 7478 patients, giving an overall yield of 1.5%. For studies ordered 72 hours after admission, the yield decreased to 0.5%. Of the patients with positive results, 102 (89%) had predisposing factors of diarrhea related to parasites including immunocompromised status, diarrhea for >7 days, or travel history (table). Excluding these patients, the diagnostic yield for remaining 10 patients was 0.1%. In 5 of these patients, positive O&P did not change management (2 with self limiting diarrhea and 3 treated for concurrent C Diff). The other patients included 1 with uncontrolled diabetes, 1 with Entamoeba Histolytica liver abscess, 1 elderly nursing home resident, 1 with cirrhosis on lactulose and 1 pregnant patient. The most common pathogens found (>25%) were Giardia, Cryptosporidia, and Strongyloides.  


Stool O&P is an overused test for patients in the emergency room and hospital with very low yield. Based on these results, the most cost-effective way of ordering stool O&P would be restricting the test to patients with a high clinical probability of positive O&P (immunocompromised status, diarrhea for > 7 days, or travel to endemic areas).

Implications for the Patient

Routine ordering of Stool O&P test is unnecessary and should be restricted to patients at risk. This can result in significant cost savings.

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