Informational Tables

Table 1.5. Rapid Diagnostic Testings

TRADITIONAL PROCEDURES

ADDITIONAL OPTIONS

COMMENTS

FECAL SPECIMENS (Permanent stained smear)

Microscopic examination of stained

fecal smear using oil immersion objectives

NOTE: Remember that the total O & P examination is recommended when the fecal immunoassays (limited to specific organisms) are negative, and the patient remains symptomatic.

FECAL SPECIMENS (Fecal immunoassays: fluorescence/microscopy, enzyme-linked immunosorbent assay/ELISA plates, lateral membrane flow immunochromatographic assay/cartridge

Fecal immunoassays (IAs) are generally simple to perform and allow for a large number of tests to be performed at one time thereby reducing overall costs. A major disadvantage of antigen detection (fecal immunoassays) in stool specimens is that the method can detect only one or two pathogens at one time. A routine ova and parasite examination must be performed to detect other parasitic pathogens. The current commercially available antigen tests (DFA, EIA or lateral flow cartridges) are more sensitive and more specific when compared to routine microscopy. Current testing is available for Entamoeba histolytica, the Entamoeba histolytica/E. dispar group, Giardia lamblia, and Cryptosporidium spp.

There are also several molecular tests that are in clinical trials for the detection of select gastrointestinal parasites. These tests are molecular gastrointestinal parasite panels and target the most commonly occurring parasitic stool pathogens.

Batch testing is possible, the methods use very few steps, and the visual assessment of positive or negative is quite easy.

These tests can be very beneficial in the absence of trained microscopists. However, in patients who remain symptomatic after a negative result, the O & P examination should always remain as an option. BOTH THE O&P EXAM AND FECAL IAs SHOULD BE A PART OF THE LABORATORY TEST MENU; SPECIFIC PATIENT HISTORIES WILL DICTATE CORRECT ORDERING OF THE MOST RELEVANT TEST OPTION.

Although tests for E. histolytica or the Entamoeba histolytica/E. dispar group are limited to the use of fresh or fresh frozen fecal specimens, they can be helpful in the absence of trained microscopists. Tests for Giardia and/or Cryptosporidium can be performed on fresh, frozen, unfixed or formalin-fixed (5%, 10%, SAF) fecal specimens. Cary Blair and some of the single vial fecal parasite fixatives can also be used. Check with the manufacturer. Parasite panels are now available for RUO testing and include: Blastocystis, Cryptosporidium, Cyclospora, Dientamoeba, Entamoeba histolytica, Giardia, Microsporidia, Strongyloides

BLOOD SPECIMENS (Stained blood films)

Microscopic examination of stained

blood films using oil immersion objectives

It is important to remember that a minimum of 300 oil immersion fields (using the 100X oil immersion objective) be examined on both thick and thin blood films.

BLOOD SPECIMENS (Rapid malaria testing

The BinaxNOW Malaria Test is a rapid immuno-diagnostic assay for differentiation and detection of circulating Plasmodium falciparum (P.f.) antigen and the antigen common to all to Pan malarial species: Plasmodium vivax (P.v.), Plasmodium ovale (P.o.), and Plasmodium malariae (P.m.) in whole blood. It is now FDA cleared (June, 2007).

Test line 1 Positive = P. falciparum

Test line 2 Positive = P. vivax, P. malariae, or P. ovale

Test lines 1,2 Positive = P. falciparum and possible mixed infection

Polymerase Chain Reactions (PCR) assays like multiplex PCR, and real time PCR has improved the sensitivity of plasmodium detection. PCR is advantageous in studying drug resistance parasites, identifying mixed infections, and in the processing of large number of samples in research and samples can be easily collected on filter papers and stored at room temperature for years. PCR has a limitation as it requires well trained staff, good laboratory infrastructure, and again a good quality assurance system. As a result, the sensitivity of different PCR methods varies In addition, PCR requires expensive equipment and well-trained technicians and is not usually adequately implemented in developing countries.

This product is positive at the following level:

0.1% (5,000/µl) = BinaxNOW

(Inverness/Binax):

Sensitivity

99.7% (P. falciparum)

93.5% (P. vivax)

Specificity

94.2% (P. falciparum)

99.8% (P. vivax)

It is important to remember that many patients may be seen who have a parasitemia much lower than the level of detection seen with the malaria rapid test. Their parasitemia may be as low as 0.01 %. Other tests are in use throughout the world but are not yet FDA cleared.

Molecular testing for Plasmodium spp. is normally used for confirmation of species, rather than for STAT malaria diagnosis. If the STAT rapid cartridge is negative, then the laboratory must implement STAT thick and thin stained blood films for diagnosis. Any blood smears requested for Plasmodium/Babesia must be ordered/collected/processed/examined/reported on a STAT basis.