Does the degree of polymerization of haptoglobin influence the results of the radial immunodiffusion assay?

The degree of polymerization of haptoglobin (Hp) phenotypes 2-1 and 2-2 was studied. In individual samples the degree of polymerization tends to be positively correlated with the Hp concentration as determined by the radial immunodiffusion technique (RID), while an inverse relationship between the size of Hp polymers and the Hp concentration in RID was expected. After reductive cleavage of Hp, the apparent Hp concentration became higher in individual samples with different degrees of polymerization; the shift to higher values appeared to be independent of the degree of polymerization in samples of phenotypes Hp 2-1 and Hp 2-2. Consequently, the degree of polymerization as such does not have an impact on the outcome of RID at a technical level.