Modification of the dextran-Mg2+ high-density lipoprotein cholesterol precipitation method for use with previously frozen plasma.
Although dextran-Mg2+ precipitation produces accurate and precise results for high-density lipoprotein (HDL) cholesterol in fresh plasma and serum, precipitation of frozen specimens with triglycerides > 2.26 mmol/L (> 200 mg/dL) is difficult. We developed a modification that dilutes thawed samples by 35% and increases dextran-Mg2+ reagent to 15% of sample volume. Standard precipitations were performed on 62 fresh EDTA-treated plasma specimens; supernatant solutions were analyzed fresh and after freezing. Standard and modified methods were also performed on thawed, paired plasmas. In specimens with triglycerides < or = 2.26 mmol/L, HDL cholesterol results for all methods were similar. For triglycerides > 2.26 mmol/L, however, bias and precision were significantly affected by freezing, and 38.5% of samples with standard precipitation required additional procedures to produce clear supernatant solutions. HDL cholesterol concentrations for thawed samples with standard precipitation were significantly greater than for fresh samples (P < 0.02), but those for the modified method were not different from fresh samples, and only one specimen required additional steps to produce a clear supernate.
McNamara
J R
JR
Lipid Research Laboratory, New England Medical Center Hospitals, Boston, MA 02111.
Huang
C
C
Massov
T
T
Leary
E T
ET
Warnick
G R
GR
Rubins
H B
HB
Robins
S J
SJ
Schaefer
E J
EJ
D011232:Chemical Precipitation; D008076:Cholesterol, HDL / Q000097:blood*; D003911:Dextrans; D004492:Edetic Acid; D006801:Humans; D008274:Magnesium; D010949:Plasma / Q000737:chemistry*; D011786:Quality Control; D012680:Sensitivity and Specificity; D014280:Triglycerides / Q000097:blood
D008076:Cholesterol, HDL; D003911:Dextrans; D014280:Triglycerides; D004492:Edetic Acid; D008274:Magnesium