Is directly measured low-density lipoprotein clinically equivalent to calculated low-density lipoprotein?
BACKGROUND
Low-density lipoprotein cholesterol (LDL-C) can either be calculated or measured directly. Clinical guidelines recommend the use of calculated LDL-C (C-LDL-C) to guide therapy because the evidence base for cholesterol management is derived almost exclusively from trials that use C-LDL-C, with direct measurement of LDL-C (D-LDL-C) being reserved for those patients who are nonfasting or with significant hypertriglyceridemia.


OBJECTIVE
Our aim was to determine the clinical equivalence of directly measured-LDL-C, using a Siemens Advia Chemistry System, and fasting C-LDL-C.


METHODS
Eighty-one subjects recruited for two cholesterol treatment studies had at least one C-LDL-C and D-LDL-C performed simultaneously; 64 had a repeat lipid assessment after 4 to 6 weeks of therapy, resulting in 145 pairs of C-LDL-C and D-LDL-C.


RESULTS
There was significant correlation between D-LDL-C and C-LDL-C (r² = 0.86). Correlation was significantly better in those with lower total cholesterol, triglycerides, and high-density lipoprotein. In 60% of subjects, the difference between D-LDL-C and C-LDL-C was more than 5 mg/dL and greater than 6%. Clinical concordance between D-LDL-C and C-LDL-C was present in 40% of patients, whereas clinical discordance was noted in 25%. One-third had greater than a 15 mg/dL difference between D-LDL-C and C-LDL-C, whereas 25% had a greater than 20 mg/dL difference. In 47% of subjects, the difference between D-LDL-C and C-LDL-C at baseline and follow-up changed by a minimum of 10% or 10 mg/dL.


CONCLUSIONS
Our findings suggest that D-LDL-C is not clinically equivalent to C-LDL-C. This puts into question the current recommendation of using D-LDL-C in situations in which C-LDL-C would be inaccurate.
James J. Peters VA Medical Center (Medical Service), 130 West Kingsbridge Road, Bronx, NY 10468, USA. lawrence.baruch@va.gov
Lawrence
L
Baruch
Sanjay
S
Agarwal
Bhanu
B
Gupta
Ann
A
Haynos
Swapna
S
Johnson
Katelyn
K
Kelly-Johnson
Calvin
C
Eng
D000368:Aged; D000924:Anticholesteremic Agents / Q000627:therapeutic use; D001774:Blood Chemical Analysis / Q000379:methods*; D002784:Cholesterol / Q000097:blood; D008078:Cholesterol, LDL / Q000097:blood*; D005260:Female; D006801:Humans; D015228:Hypertriglyceridemia / Q000188:drug therapy; D008075:Lipoproteins, HDL / Q000097:blood; D008077:Lipoproteins, LDL / Q000097:blood*; D008297:Male; D008875:Middle Aged; D013810:Therapeutic Equivalency; D014280:Triglycerides / Q000097:blood
D000924:Anticholesteremic Agents; D008078:Cholesterol, LDL; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D014280:Triglycerides; D002784:Cholesterol