Dear Juan, 

LDL particles have a mass and size distribution, and for LDL the density range usually accepted is within 1.019-1.063 g/mL and a particle size between 18-25 nm. Studies dating back the '80 described the predominance of smaller and denser LDL particles in atherosclerotic patients, and later lead to the development of the Lipoprint (Quantimetrix) to estimate the predominance of LDL with pattern A or pattern B in blood, and thus the risk to atherosclerosis. In my own experience it is not quite clear to me whether there are defined boundaries (namely specific values) to classify small and dense LDL (SD-LDL). I've looked into this some time ago and found that the density cut-off for SD-LDL was 1.040g/mL (originally defined by Krauss and Burke, 1982). Other authors, have decided on more defined values for LDL subfractions (Chapman et al., 1988, JLR, 29; Graaf et al., 1991, ATVB, 11; Nikon et al., JLR, 1991, 32; Skoglund-Anderson et al., 1999). I believe this to be a exciting topic to pursue with the novel Omic approaches in search of the atherogenic properties of lipoproteins. Hope this helps,

Ana

Because it is compared to other LDL particles! Lipoproteins are heterogeneous and this have a density range. Amongst this heterogeneous group, some are more dense than others within the specified range.

http://www.ncbi.nlm.nih.gov/pubmed/24569029

In this article you will find several references for the characterization of small dense LDL.The cut off depends on the method (gel electrophoresis, ultracentrifugation, NMR). In the supplement of this article the authors published data of the composition of several lipoprotein classes.

Dear Professor Gomez Gerique

Hi

It's the density of lipoproteins in plasma:

 VLDL, d

Dear Juan, 

LDL particles have a mass and size distribution, and for LDL the density range usually accepted is within 1.019-1.063 g/mL and a particle size between 18-25 nm. Studies dating back the '80 described the predominance of smaller and denser LDL particles in atherosclerotic patients, and later lead to the development of the Lipoprint (Quantimetrix) to estimate the predominance of LDL with pattern A or pattern B in blood, and thus the risk to atherosclerosis. In my own experience it is not quite clear to me whether there are defined boundaries (namely specific values) to classify small and dense LDL (SD-LDL). I've looked into this some time ago and found that the density cut-off for SD-LDL was 1.040g/mL (originally defined by Krauss and Burke, 1982). Other authors, have decided on more defined values for LDL subfractions (Chapman et al., 1988, JLR, 29; Graaf et al., 1991, ATVB, 11; Nikon et al., JLR, 1991, 32; Skoglund-Anderson et al., 1999). I believe this to be a exciting topic to pursue with the novel Omic approaches in search of the atherogenic properties of lipoproteins. Hope this helps,

Ana

Thanks for sharing these interesting inputs Ana.