Clinical Chemistry, Vol 21, 183-185, Copyright © 1975 by the American Association for Clinical Chemistry

Improved Method for Densitometry of Electrophoretic Lipoprotein Fractions

¹ Baylor College of Medicine, Department of Rehabilitation, Houston, Tex. 77025, and Millipore Biomedica, Acton, Mass. 01720.

We evaluated a method for the densitometric quantitation of the electrophoretic lipoprotein fractions that sets the limit of integration at the beta-lipoprotein peak maximum. Results were compared with the more conventional method of placing the limit of integration in the valley between the beta- and pre-beta-lipoprotein peaks. The criterion of symmetrical beta-lipoprotein peaks imposed by the method was tested, and manual determination of the beta peak maximum was compared to automatic computer analysis. Computer-generated curves simulating increasing overlap of constant shape beta and pre-beta peaks were analyzed by the two methods. The conventional method introduces an error that increases with increasing overlap, but with the present method results agreed with those for completely resolved peaks. The beta peak was best approximated by an isosceles triangle (at least for the electrophoresis technique used in these studies), indicating symmetry of the beta peak. Values for the area under the lipoprotein peaks obtained by manual and computer placement of the integration limits agreed well (r = .892 to .998; SE of estimate = .0264 to .0306). The "beta peak maximum" method of densitometric quantitation avoids the problems associated with partial resolution of the beta- and pre-beta-lipoproteins. It is equally adaptable to either visual placement of the limits of integration or computer analysis.