low density lipoproteins are directly determined in fluid samples by selectively precipitating low density lipoproteins from the sample by forming clusters , selectively consuming the high density and very low density lipoproteins , and resolubilizing the low density lipoproteins for direct determination thereof . the clusters are formed by treating the fluid sample with a mixture of a polyanionic compound , a divalent metal , and a nucleating agent . the clusters are redissolved and assayed for low density lipoproteins .