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Presentation of Quiz #2

The Microbiology section has just decided to incorporate immunoassays for Giardia lamblia and Cryptosporidium parvum into the laboratory test menu. The laboratory is also considering the addition of tests for the Entamoeba histolytica/Entamoeba dispar group and the true pathogen, Entamoeba histolytica. What factors should be considered prior to implementation of these immunoassays? Please comment on the issues presented below.

It is important to remember that the immunoassay tests currently available are not designed to "take the place" of the Ova and Parasite examination (O&P) (direct wet smear [fresh specimen only], concentration, and permanent stained smear). Both the O&P examination and the immunoassays for intestinal protozoa should be separate orderable, billable tests.

Test kit options and specimen collection requirements

Test ordering menu

Test coding

Test report formats

Client education

Personnel expertise

Geographic area

Scroll Down for Answer and Discussion

 

 

 

 

 

 

Answer and Discussion of Quiz #2

Because there are so many variables to consider when introducing new tests into the laboratory, it is reasonable to assume that not every laboratory will offer the same test menu. There are very specific reasons for selection and/or nonselection of new methods. Some of these factors include: geographic location and presence of the parasites being considered, patient populations (local, national, and/or international), size of the laboratory and number of specimens submitted, clients serviced, number of tests ordered, availability of trained personnel, trained consultants for trouble-shooting technical problems, client educational options, etc. If we examine the various issues surrounding the list presented above, this information may help you in assessing whether or not your laboratory should introduce newer testing options for some of the intestinal protozoa.

Test kit options and specimen collection requirements: All immunoassay kits can be used with fresh or frozen specimens; however, only the kit formats that include Giardia lamblia and Cryptosporidium parvum can be performed using formalinized specimens (5% or 10% formalin, sodium acetate-formalin-acetic acid [SAF], and some of the single vial collection systems) (TOTAL-FIX). If testing is performed for the Entamoeba histolytica/Entamoeba dispar group or the true pathogen, Entamoeba histolytica, fresh or frozen specimens ONLY can be used.

NOTE: All available commercial immunoassay kits for the detection of antigen or actual organisms (cysts and/or oocysts) have published reports of both sensitivity and specificity of approximately 95% or better. A positive immunoassay result does NOT require confirmation testing by the O&P exam.

TEST KIT OPTIONS

PROS

CONS

Enzyme Immunoassay (EIA)

Easy to use, can batch test

Minor color differences may be difficult to interpret; thorough washing mandatory.

Fluorescent Antibody (FA)

Easy to read; combination reagent available for both Giardia and Cryptosporidium; visual identification of cysts and oocysts (different sizes and shapes); can batch test

Requires fluorescent microscope; cost may be a factor.

Cartridge, EIA or Chromatographic IA

Ease to use and read; combination reagents available for Giardia, Cryptosporidium, E. histolytica/E. dispar group, or E. histolytica; can batch test

 

Test ordering menu: Depending on the patient history, it may be appropriate to order immunoassays for very specific organisms. However, it may be more important to order the O&P examination, particularly if the patient has been in a geographic area where parasites other than Giardia and/or Cryptosporidium may be present. Remember, these tests should always be separate orderable, billable tests. Refer to INFORMATION TABLES for a thorough discussion of STOOL TESTING RECOMMENDED ORDERS.

Test Coding: It is important for billing purposes to use separate codes for the O&P examination, as well as separate codes for the EIA, FA, or cartridge immunoassays.

Test report formats: When reporting results of the O&P examination, it is important to inform the physician that Cryptosporidium parvum (with rare exceptions), Cyclospora cayetanensis and the microsporidia will not be detected from the routine O&P examination; special procedures must be ordered (modified acid-fast stains for the coccidia and modified trichrome stains for the microsporidia). When reporting results of the stool immunoassays, it is important to inform the physician that these procedures are designed to detect certain organisms ONLY. Indicate that a negative report means that specific organisms (name the organisms) were not seen.

Client education: Since the laboratory does not have sufficient patient information on which to base laboratory orders, it is mandatory that the physician clients have appropriate and complete information related to test ordering options. They should thoroughly understand the pros and cons of the O&P examination compared with the immunoassays; specific orders for one or the other are relevant, depending on the patient history. Some of the considerations include: patient's immune status, geographic area, travel history, and a history of daycare. One of the most important considerations is the following: IF THE PATIENT BECOMES ASYMPTOMATIC AT THE POINT AT WHICH NEGATIVE LABORATORY RESULTS ARE REPORTED, NO FURTHER TESTING IS REQUIRED; IF THE PATIENT REMAINS SYMPTOMATIC, THEN ADDITIONAL TESTING IS WARRANTED.

Personnel expertise: The performance of stool immunoassay testing is not difficult, providing the manufacturer's directions are followed. Thorough washing during EIA testing will eliminate the possibility of incorrect results. Known positive and negative specimens should be tested as a part of the learning phase.

Geographic area: STOOL TESTING RECOMMENDATIONS are based partly on the location of the laboratory and travel history of the patients. Again, it is important to provide specific guidelines on test ordering options for the physicians; adequate information will help ensure appropriate laboratory testing and clinically relevant information for quality patient care.

 Additional Reading:

  1. Garcia, LS, 2016. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, DC.

 

We hope this discussion (Quiz #2) has been helpful. Don't hesitate to contact us if you have questions and/or suggestions: LynneGarcia2@verizon.net