Marker-free immunological analytical methods.

The antigen-antibody reaction itself acts as the "marker system" in the marker-free immunological methods. This group of analytical techniques includes radial immunodiffusion, nephelometry, turbidimetry and nephelometric inhibition. The Particle Counting-Immunoassay (PACIA) technique also belongs to this group, although it employs latex particles as markers for the intensification of the indicator reaction. The principles of the above methods are described, and their applications in diagnosis, their detection limits and important interfering factors are discussed. For all methods, the precision in series and from day to day is in the range of 5-10%. The detection limits are 1 ng/l for the PACIA technique, 10 micrograms/l for nephelometric inhibition, 1 mg/l for nephelometry as an end point technique, and 10 mg/l for for nephelometry as a kinetic technique. Commercial sources of reagents and apparatus are given in an appendix.