[2] In diagnostic nephelometry, the ascending branch of the Heidelberger-Kendall curve is extended by optimizing the course of the reaction so that most plasma proteins’ (from human blood) measurement signals fall at the left side of the Heidelberger-Kendall curve, even at very high concentrations.
It is based on the principle that a dilute suspension of small particles will scatter light (usually a laser) passed through it rather than simply absorbing it.
[3] Antibody and the antigen are mixed in concentrations such that only small aggregates are formed that do not quickly settle to the bottom.
However, the large particles will fall out of the solution and cause a false scatter reading, thus kinetic nephelometry was devised.
As long as the reagent is constant the rate of change can be seen as directly related to the amount of antigen present.