Low-density-lipoprotein apoprotein B in plasma as measured by radial immunodiffusion and rocket immunoelectrophoresis

Radial immunodiffusion (RID) and rocket immunoelectrophoresis (RIE) are compared with respect to determination of LDL-bound apo B in plasma. Isolated VLDL could not enter a 15 g/L agarose gel when either technique was used. However, in the presence of plasma proteins, migration of VLDL into agarose was enhanced. Only when plasma samples were kept frozen before the assay was plasma VLDL unable to enter the agarose gel when RID was used. With RIE the contribution of plasma VLDL to the apo B determination under these conditions was not always negligible. Besides enhancing the entry of VLDL into the agarose, the presence of proteins also influences apo B immunoreactivity of LDL and VLDL. For measuring LDL-bound apo B directly in unfractionated plasma we recommend: (a) RID in 15 g/L agarose gel; (b) freezing the plasma samples before assay; (c) diluting the plasma samples in saline supplemented with protein in the same concentration as is present in plasma (70 g/L); and (d) using plasma as the assay standard.