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A particle gel assay was sensitive and specific for the detection of T. pallidum antibodies.
Evaluation of a new particle gel immunoassay for determination of antibodies against Treponema pallidum.
Schmidt BL.
Journal
of Clinical Microbiology 2004;42:2833-85.
Summary:
Question
What is the performance of a new particle gel immunoassay compared to other immunoassays for the diagnosis of syphilis?
Design
The results of a particle gel immunoassay (PaGIA) were compared to those of six other assays including a passive particle agglutination test, an ELISA, the FTA-ABS, the VDRL, an IgM antibody assay, and the 19S IgM FTA-ABS for the diagnosis of syphilis in serum samples from patients with untreated primary, secondary, early latent, and neurosyphilis and from patients without syphilis.
Participants
One hundred twenty four serum samples from untreated patients, including 60 from patients with primary syphilis, 27 from patients with secondary syphilis, 32 from patients with early latent syphilis of less than one year (all reactive in the FTA-ABS and in two IgM-specific tests), and 5 from patients with neurosyphilis were
tested. Clinical diagnoses were confirmed by dermatologists and/or neurologists.
Four hundred ninety serum or plasma including 432 from patients with no history of syphilis (all nonreactive in the particle agglutination test and ELISA), 20 from patients with confirmed Lyme borreliosis (all negative in the particle agglutination test and FTA-ABS), and 38 from patients without syphilis but whose sera were positive by the FTA-ABS (n=7), the VDRL (n=25), or the ELISA (n=6) were tested.
Description of Tests and Diagnostic Standard
The PaGIA (DiaMed, Cressier sur Morat, Switzerland) for the detection of T. pallidum antibodies is a new particle immunoassay that consists of a microtube containing a gel matrix and red polymer particles sensitized with three recombinant antigens, TpN15, TpN17, and TpN47, in a ready to use
suspension. The assay was performed as recommended by the manufacturer with 10
µL of serum or plasma pipetted into the funnel of the
tube. Particles were added, the tubes incubated for 5 min and then
centrifuged. Results were read visually: positive results were indicated by a tight red line on the top of the gel surface, negative results by the presence of a pellet of colored particles at the bottom of the
tube. Other tests for syphilis antibodies were the particle agglutination test, Serodia TP-PA (Fujirebio), the ELISA, ICE-Syphilis (Abbott-Murex), the
FTA-ABS (Biomerieux) the VDRL (Dade
Boehring), the IgM-specific antibody tests Mercia Syphilis M (Microgen Bioproducts, Camberley, UK) and 19S IgM FTA-ABS.
Main Outcome Measures
The results obtained by the PaGIA method were compared to those obtained by the VDRL, TP-PA, and ELISA assays.
Main Results
The sensitivities of the PaGIA and the other tests performed are shown in the
table. There were no significant differences in sensitivity between the PaGIA and the treponemal tests
compared. Of the 92 sera from patients with primary or early latent syphilis, 10, 15, and 5 were negative by PaGIA, VDRL, and TP-PA,
respectively. Eight of the 15 VDRL negative samples were also negative by
PaGIA. Among the 5 sera negative by TP-PA, 4 were also negative by VDRL and 2 of those 4 were negative by
PaGIA. One of the 490 sera from patients without syphilis was positive by the PaGIA
method. The PaGIA yielded a specificity of 99.8%. The positive and negative predictive values were 99.1 and 98%, respectively.
Sensitivities of four serologic tests with 124 serum samples from untreated patients with syphilis.
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Syphilis disease stage
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Sensitivity (%)
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TP-PA
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VDRL
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PaGIA
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ELISA
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Primary
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93.3
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80
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88.3
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88.3
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Secondary
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100
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100
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100
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100
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Early latent
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96.9
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90.6
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90.6
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96.9
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Neuro
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100
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100
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100
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100
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All
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96
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87.8
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91.9
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93.5
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Authors ' Conclusions
The PaGIA offered excellent specificity and a sensitivity similar to that of other treponemal
tests. The advantages include simplicity of operation and a reaction time of only 20 min.
Source of funding: None given.
For correspondence: Bruno L. Schmidt, Department of Dermatology, Hospital of the City of Vienna-Lainz, 1, A-1130 Vienna,
Austria. E-mail address:
bruno.schmidt@kavwien.at.
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