Submission of stool specimens

Result or situation

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Interpretation discussion

Submission of a single stool specimen for ova-and-parasite examination

One stool specimen is not sufficient for the recovery of intestinal parasites (only a 50% recovery); 2 specimens are recommended, while 3 offers the best chance of organism recovery (approximately >95% recovery)

While 3 specimens collected over a 10-day period is the best approach, receipt of 2 specimens is acceptable

Submission of 2 stool specimens for ova-and-parasite examination

Although submission of 2 stool specimens is acceptable, 3 specimens collected over a 10-day period provide the best approach for organism recovery.

While 2 specimens are now considered acceptable, 3 specimens will allow the most complete percentage recovery of intestinal parasites present.

Examination of fecal specimens

Result for ova-and-parasite examination

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No parasites seen

Antibiotics such as metronidazole or tetracycline may interfere with the recovery of intestinal parasites, particularly the protozoa.

If a patient is symptomatic and intestinal parasites are suspected, this comment may be helpful for the physician, particularly if the patient has received any of these antibiotics.

Yeasts, budding yeasts, and/or pseudophyhae (report if moderate, many, or packed)

Reports of yeasts may or may not be clinically relevant due to possible specimen handling delays prior to fixation.

Some laboratories do not report yeast due to potential interpretation errors; they may call the physician directly. Because yeasts can continue to grow within the stool prior to fixation, the results from the permanent stained smear may or may not be clinically relevant. Quantitate if moderate, many, or packed. Some laboratories prefer to discuss this finding with the clinician rather than reporting via the standard reporting process.

Entamoeba histolytica
Trophozoites containing ingested RBCs or a positive result with the antigen detection kit for the true pathogen Entamoeba histolytica or positive molecular testing for E. histolytica, including molecular GI panels

Pathogenic; cause of amebiasis

Result based on presence of ingested RBCs within the trophozoite cytoplasm and/or a positive result using the fecal immunoassay specific for the pathogen Entamoeba histolytica and/or a positive result using molecular testing for E. histolytica

Result for ova-and-parasite examination

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Entamoeba histolytica/E. dispar group


Trophozoites (containing no ingested RBCs) and/or cysts; morphology consistent with the group or a positive result using the fecal immunoassay specific for the group only.

Differentiation between the pathogen Entamoeba histolytica and the nonpathogen Entamoeba dispar is not possible based on organism morphology; if ingested RBCs are NOT seen, unable to differentiate the two organisms OR
Unable to determine pathogenicity from organism morphology OR
depending on patient’s clinical condition, treatment may be appropriate.

A fecal immunoassay specific for the pathogen, Entamoeba histolytica, can be performed on fresh stool to separate out E. histolytica and E. dispar
◩ NOTE: Could be added as another comment if the test is offered (see below)

Differentiation of E. histolytica from E. dispar

To determine the presence or absence of Entamoeba histolytica, submit a fresh stool specimen.

The fecal immunoassay specific for Entamoeba histolytica requires fresh or frozen stool for testing.

In some cases, a specimen received in Cary-Blair medium is acceptable; check package insert.

Blastocystis spp. is recommended

Blastocystis spp. contains approximately 17 different subtypes, none of which can be differentiated on the basis of organism morphology; some subtypes have been found to cause symptoms and some have not. If no other pathogens are found, Blastocystis may be the cause of patient symptoms
AND
Other organisms capable of causing diarrhea should also be ruled out.
OR
Clinical significance may be relevant; approximately half of the human subtypes may cause symptoms
OR
Status as a pathogen remains controversial; approximately half of the human subtypes can cause symptoms, while half do not

Until there are testing options to differentiate between the subtypes, it is important that the physicians know that some subtypes of Blastocystis may cause symptoms. Quantitate these organisms (rare, few, moderate, many, packed).

Report comments are highly recommended, particularly if the term Blastocystis hominis rather than Blastocystis spp. is used.

Blastocystis spp. is recommended

Result for ova-and-parasite examination

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Interpretation discussion

Giardia lamblia (G. duodenalis, G. intestinalis)
Other names which refer to the same organism, Giardia lamblia, include the following:

Giardia duodenalis

Giardia intestinalis

Pathogenic

If fecal immunoassays are performed, the testing of two separate stools (collected at least 1 day apart) is recommended before the patient is considered negative. The testing of two stools is not required for Cryptosporidium spp.

Entamoeba hartmanni

Entamoeba coli

Entamoeba moshkovskii

Entamoeba bangladeshi

Endolimax nana

Iodamoeba büetschlii

Chilomastix mesnili

Pentatrichomonas hominis

Enteromonas hominis

Retortamonas intestinalis

Trophozoites and/or cysts

Nonpathogenic; treatment not recommended; however, recovery of these organisms indicates that the patient has ingested something contaminated with fecal material (same infectivity route for pathogens); continued research may require revision of nonpathogenic vs pathogenic classifications.

It is important to report nonpathogens; the patient may be infected with one or more pathogens not yet found.

Result for ova-and-parasite examination

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Microsporidia (fecal and urine specimens)

The report would indicate “Microsporidian spores present”

These are the two most likely organisms present; these comments are very helpful, especially in indicating that the two organisms cannot be identified to the genus or species levels on the basis of calcofluor white or modified trichrome-stained smears.

Enterocytozoon bieneusi

Encephalitozoon intestinalis

“Probably Enterocytozoon bieneusi or Encephalitozoon intestinalis or both; these tend to disseminate from the GI_a tract to the kidneys. Identification to the genus/species level not possible from stained smears.”
Other Encephalitozoon spp. are also more likely to be found in urine; however, they cannot be differentiated on the basis of light microscopic morphology.

a GI, gastrointestinal.

Examination of blood specimens

Result

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No parasites seen

The submission of a single blood specimen will not rule out malaria; submit additional bloods every 4–6 h for 3 days if malaria remains a consideration

It is important to make sure the physician knows that examination of a single blood specimen will not rule out malaria. Often an alternate suspected diagnosis is determined based on additional laboratory results. Some recommend a longer time frame between blood draws (12-24 hr).

Plasmodium spp. seen

Unable to rule out Plasmodium falciparum or Plasmodium knowlesi

Since P. falciparum and P. knowlesi cause the most severe symptoms, it is important to let the physician know that these species have NOT been ruled out.

Plasmodium spp. seen_a

No gametocytes seen

It is important when reporting Plasmodium spp. to indicate the presence or absence of gametocytes; these findings will influence therapy and/or issues of transmission. The approach to the patient will also vary, depending on the geographic area and Plasmodium spp. detected

Plasmodium spp., possible mixed infection

Unable to rule out Plasmodium falciparum or Plasmodium knowlesi

Since P. falciparum and P. knowlesi cause the most severe symptoms, it is important to let the physician know that these species have NOT been ruled out. Consider PCR for identification to species.

Plasmodium vivax

Sequelae from this infection may be more serious than once suspected.

Increasing reports of clinical severity with complicated and lethal cases have modified the perception that infection with P. vivax is benign.

Result

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Plasmodium malariae or P. falciparum

Unable to rule out Plasmodium knowlesi; confirm travel history to Malaysia or neighboring areas

If the patient has traveled to the area where P. knowlesi is endemic, it may be impossible to differentiate between P. falciparum (rings only), P. malariae (band forms), and P. knowlesi. Consider PCR for identification to species.

Negative for parasites using automated hematology instruments

Automated hematology instruments will not detect low malaria parasitemias seen in immunologically naïve patients (travelers)

Patients who have never been exposed to malaria (immunologically naïve) will become symptomatic with very low parasitemias that will not be detected using automation (0.001 to 0.0001%)

Negative Plasmodium rapid test (BinaxNOW rapid test, FDA cleared)^b

This test is most sensitive at a parasitemia of 0.1% (>5,000/μl) for P. falciparum and P. vivax. Many patients who have never been exposed to malaria (immunologically naïve) will become symptomatic with very low parasitemias that will not be detected using the rapid malaria test (BinaxNOW).

It is VERY IMPORTANT to remember that many travelers who have never been exposed to malaria (immunologically naïve) will become symptomatic with very low parasitemias that will not be detected using the rapid malaria test (BinaxNOW).

If negative, then it is mandatory that STAT thick and thin blood films be prepared, examined, and reported.

If positive, then confirmation of the Plasmodium spp. should be obtained.

Additional testing required for identification confirmation.

Microscopic and/or molecular confirmation may be required.