A rational approach to the stool ova and parasite examination.
BACKGROUND
Examination of multiple stool specimens per patient to rule out parasitic infection continues to be recommended in the literature. Attractive alternatives have been proposed, such as examination of a single specimen, but data to support their use have been inconclusive.


METHODS
We reviewed the results of comprehensive stool ova and parasite examinations performed during a 1-year period to determine the incremental value of examining >1 specimen. Next, we implemented rejection criteria, allowing analysis of only a single specimen in most cases, and studied the impact of the change by reviewing data from a subsequent year.


RESULTS
Prior to implementation of rejection criteria, 91% of parasites were detected in the first specimen submitted, although many clinical evaluations (72%) involved the submission of only 1 stool specimen. When at least 3 specimens were submitted, the sensitivity of examining the first in the series was 72%. Even the latter sensitivity provides negative predictive values of approximately 98%, approximately 97%, approximately 95%, or approximately 93% when the prevalence of parasites among those tested is 5%, 10%, 15%, or 20%, respectively. Examination of additional specimens after examination of the first specimen that yielded a positive finding revealed previously undetected parasites in only 10% of cases. After the application of rejection criteria, the parasite detection rate did not change significantly.


CONCLUSIONS
Comprehensive examination of a single stool specimen is sufficient for most patients, when the prevalence of infection among the tested population is up to 20%. Rational use of the stool ova and parasite examination relies on communication between clinician and laboratory, and retention of deferred specimens in case examination of additional specimens is clinically warranted.
Branda
John A
JA
Department of Pathology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA.
Lin
Tai-Yuan David
TY
Rosenberg
Eric S
ES
Halpern
Elkan F
EF
Ferraro
Mary Jane
MJ
D000818:Animals; D016785:Cryptosporidium parvum / Q000302:isolation & purification; D004029:Dientamoeba / Q000302:isolation & purification; D005243:Feces / Q000469:parasitology*; D016829:Giardia lamblia / Q000302:isolation & purification; D006801:Humans; D010270:Parasite Egg Count; D010271:Parasites / Q000187:drug effects