Itpa index

Author: Prof. Dr. med. Peter Altmeyer

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Last updated on: 29.10.2020

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iTPA is the acronym for "intrathecal produced T. pallidum antibodies". It is used to assess neurosyphilis and is calculated as follows:

TPHA titre (CSF) / total IgG (CSF) × total IgG (serum) / TPHA titre (serum)

General information
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In the absence of antibody production against Treponema pallidum in the CNS, the ITpA index is 1 (0.5-2.0). A value > 2.0 indicates a specific antibody synthesis in the CNS, a value > 3.0 proves it with high reliability (sensitivity 84%, specificity 100%). If the ITpA is not calculated by ELISA but by titer levels, only a value > 4 is considered to be proof of autochthonous pathogen-specific antibody production due to the higher inaccuracy.

False-negative findings occur in secondary stage CNS infections and in vasculitic neurosyphilis.

Since the ITpA index and TPHA-AI (= modified ITpA index according to Reiber) only normalize over the course of years to decades after therapy, these antibody specificity indices (ASI) are not suitable as activity parameters.

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  1. Luger AF et al (2000) Significance of laboratory findings for the diagnosis of neurosyphilis. Int J STD AIDS 11:224-234.
  2. Prange HW et al (1983) Relationship between neurological features and intrathecal synthesis of IgG antibodies to Treponema pallidum in untreated and treated human neurosyphilis. J Neurol 230:241-252.

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Treponema pallidum;


Last updated on: 29.10.2020