The Microbiology section has just decided to incorporate immunoassays for Giardia lamblia and Cryptosporidium spp. 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?
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 and should be available to your clients on your test menu.
Please comment on the issues presented below.
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Answer and Discussion of Quiz #46
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, even if some of the tests are sent to a reference laboratory. 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 spp. can be performed using formalinized specimens (5% or 10% formalin, sodium acetate-formalin-acetic acid [SAF], and some of the single vial collection systems), particularly the Universal Fixative (TOTAL-FIX). If testing is performed for the Entamoeba histolytica/Entamoeba dispar group or the true pathogen, Entamoeba histolytica, fresh or frozen specimens or those in Cary Blair can be used; these kits are not compatible with stool submitted in ANY of the fixatives.
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. Positive or negative immunoassay results do NOT require confirmation testing by the O&P exam. However, when testing for Giardia, if the first test is negative, order a second stool before calling the patient negative. This is due to the variability in shedding seen in Giardia infections (not necessary with Cryptosporidium spp.).
Test Kit Options |
Pros |
Cons |
Enzyme Immunoassay (EIA) |
Easy to use, can batch test |
Color for low positives may be difficult to interpret if read manually rather than using instrumentation; 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; perform on stool concentrates |
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 |
If the cartridge contains reagents for the detection of the E. histolytica/E. dispar group or E. histolytica, fresh or frozen stools or those in Cary Blair will be required |
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. 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 spp. (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 RECOMMENDED ORDERS 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.
We hope this discussion (Quiz #46) has been helpful. Don't hesitate to contact us if you have questions and/or suggestions: LynneGarcia2@verizon.net
An ordering table can also be sent if requested from Lynne Garcia (via Email address). Specific recommendations for the performance of fecal immunoassays can be seen below.
Enzyme immunoassays (antigen detection, no centrifugation recommended)
Fluorescence (visual identification of the organisms)
Lateral Flow Cartridges (antigen detection, no centrifugation recommended)
STOOL TESTING RECOMMENDED ORDERS
References:
Each Quiz has a two section format: the first section will present the Quiz topic and the second section will provide a discussion of the answer and/or various options in response to the Quiz situation presented to the user. In some situations, there may be more than one correct response.
The content within this site is made possible through the extensive contribution of Lynne S. Garcia, M.S., MT(ASCP), CLS(NCA), BLM(AAB), F(AAM), Director, Consultantation and Training Services (Diagnostic Medical Parasitology and Health Care Administration). For additional information, she can be contacted at LynneGarcia2@verizon.net.
Reference: Garcia, L.S. 2015. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, D.C.