Testing:
(1) Antibody levels against toxoplasma antigens are determined in serum and aqueous humor (or other body fluid).
(2) If the antibody level is expressed in titers, then the titer value is the inverse of the serologic titer for the fluid (for titers of 1:X, the titer value is X). If antibody levels are determined by a method giving results directly proportional to the antibody concentration, then these may be directly entered.
(3) The total amount of immunoglobulin is measured in both the serum and the aqueous humor (or body fluid). An alternative is to evaluate only a single subset (IgM or IgG).
aqueous humor antibody coefficient (C) =
= ((anti-toxoplasma antibody titer value for aqueous humor) * (immunoglobulin concentration in the serum as g/dL)) / ((anti-toxoplasma antibody titer value for serum) * (immunoglobulin concentration in the aqueous humor as g/dL))
Interpretation:
• A value of C >= 8 is serologic evidence for ocular toxoplasmosis.
• A value of C from 2-7 is suggestive of ocular toxoplasmosis; some local production of antibody is possible but experimental error could also be present.
• A value of C < 2 does not support the diagnosis of ocular toxoplasmosis.
