1. Which organisms is the Directigen Meningitis Combo Test intended to detect?
The Directigen Meningitis Combo Test Kit detects S. pneumoniae, H. influenzae type b, N. meningitidis Groups A, B, C, Y, and W135, Group B Streptococcus, and E.coli K1.
2. What is the test format?
The Directigen Meningitis Combo Test is a rapid, latex slide agglutination tests for qualitative detection of antigen directly from clinical specimens.
3. What is the source of sample for the tests?
CSF (cerebrospinal fluid), urine (except infant urine), and serum
4. What is the antibody source used for the test?
- Rabbit polyclonal, purified antisera are used for H. influenzae type b, S. pneumoniae, Group B Streptococcus, N. meningitidis Groups C, W135, A and Y.
- Mouse monoclonal is used for N. meningitidis Group B and E. coli K1.
5. Will the Directigen Meningitis Combo Test Kits replace the need to culture for bacterial pathogens?
No. Traditional culture methods should still be performed.
6. What lab equipment will be required to perform the Directigen Meningitis Combo Test?
A lab rotator, timer, standard micropipettor, boiling water bath (or heat block), centrifuge, and high intensity incandescent lamp are needed.
7. Why has BD decided to offer individual meningococcus reagents for Groups A and Y, B, and C and W135 rather than one N. meningitidis Polyvalent reagent?
Individual reagents are offered to optimize sensitivity. Also, having individual reagents allows you to simultaneously identify and group the causative organism.
8. Can I test synovial fluid/ pleural fluid/ pericardial fluid/ amniotic fluid, etc?
Testing other body fluids is not a recommended procedure.
9. How much technologist time is involved in the test?
Usually, less than five minutes of tech time is required.
10. Is any pretreatment of the CSF specimen necessary?
Yes. The CSF should be heated at 100ºC for three minutes in a boiling water bath or heat block. Note: The N. meningitidis B reagent must be used only with unheated CSF.
11. Must I wait for culture results before reporting Directigen Meningitis Combo Test results?
If the test is positive, identification may be reported at once so appropriate antimicrobic therapy can begin. If culture results differ with assay results, this also must be reported.
12. How easy is the test to read?
Any agglutination is reported as positive, so the test is very easy to interpret. No grading of reactions (1+, 2+, etc.) is necessary. Negative results are smooth.
13. I got a positive N. meningitidis B test. When I grew the organism in culture, it turned out to be E. coli K1. What's wrong with the kit?
Nothing. The antigens on the surface of N. meningitidis B and E. coli K1 are structurally identical and therefore no immunologic test will distinguish them.
14. Can I make a saline suspension of organisms off a culture plate and test with your product?
No.
15. Could antigen remain in urine two months after treatment?
There is no data to document how long the various antigens could persist in the urine following treatment.
16. Could a patient who has recently been vaccinated for H. influenzae B give a false positive result for H. influenzae in CSF?
t is unlikely that the antigen would cross the blood/brain barrier but possible, if the barrier is broken (especially by another infective organism or trauma).
17. Would a CSF specimen that has been kept at room temperature over 48 hours be a valid sample for testing ?
We recommend freezing CSF for long storage to prevent contamination or significant antigen degradation. If a sample cannot be run stat, CSF can be stored at 2-8ºC for up to 48 hours or frozen at -20ºC.
18. What affect would incubation of a CSF specimen at 37ºC for 24 hours or more have on Directigen testing?
We do not recommend this procedure.
19. Can CSF specimens be centrifuged if turbid or bloody before running the test kits?
Turbid CSF should be centrifuged after heating and before testing. Bloody CSF is not recommended for testing.
20. Can incorrect results be obtained when using stock cultures?
Stock cultures that have been replated a multitude of times might lose the ability to produce capsular antigens. The capsular antigens are the main antigens that the latex reagents specific for H. influenzae type b, N. meningitidis, and S. pneumoniae detect.
21. Why do the positive reactions look different with each latex reagent?
The appearance of the positive reaction looks different due to the different monoclonal/polyclonal antibodies used, sizes and epitopes of the antigen, and the type of latex used for the reagents.
22. Why must specimen buffer be added to serum specimens?
Specimen buffer is added to serum specimens to reduce the size of the clotted pellet after the heating step denatures the proteins. This will enable the user to have enough fluid to run the test kit.
23. Why shouldn't heated CSF be used when testing with the N. meningitidis B reagent?
The N. meningitidis B antigen is somewhat heat labile. This is due to the nature of the antigen's chemical structures and how it reacts in its environment.
24. N. meningitidis Group B, antibody-coated latex will cross react with antigen from E. coli K1. What percentage of all neonatal E.coli are E.coli K1?
The antigen detected is N-acetyl-neuraminic acid. This antigen is common to both these organisms.84% of all neonatal E.coli are E. coli K1. (New England Journal of Med.: May 30, 1974) All known current latex kits on the market experience cross reactivity with E. coli K1.
25. How important is the concentration of urine? Do you recommend testing urines concentrated or unconcentrated?
The sensitivity data in our package insert indicate that the Directigen reagents are extremely sensitive when testing unconcentrated urine specimens. Concentration of urine specimens may be advisable early in the course of disease or for detection of antigens when the organism numbers may be low.
