754
Assessment of the Agreement between the LDL Genzyme Assay and LDL Measured by Ultracentrifugation and the Applicability of the Friedewald Equation for Calculating LDL Measurements: ACTG A5087
Scott Evans*1, C Fichtenbaum2, W Meyer3, M Caulfield3, J Aberg4, and ACTG 5087 Study Team
1Harvard Sch of Publ Hlth, Boston, MA, US; 2Univ of Cincinnati, OH, US; 3Quest Diagnostics, Baltimore, MD, US; and 4New York Univ, NY, US
Background: Hypertriglyceridemia
is a frequent problem in HIV-infected individuals on ART. Triglyceride (TG)
levels >400 mg/dL render determination of
sow-density lipoproteins (LDL) by the Friedewald
equation inaccurate. Thus, LDL must be measured directly in such persons. The
reference method for direct measurement is ultracentrifugation, which is not
widely available. A commercially available direct LDL test kit utilizes an
enzymatic method (Genzyme) though data are lacking on
its clinical utility in patients with high TG. The objective of this study was
to compare the agreement of the Genzyme direct assay
and the Friedewald equation with the reference
ultracentrifugation method in the estimation of LDL concentrations.
Methods: Overnight fasting screening and week 12
samples were tested from subjects being evaluated and enrolled in ACTG 5087, a
randomized clinical trial to determine whether fenofibrate
is non-inferior to pravastatin for the management of
HIV-related combined hyperlipidemia. Screening and
week 12 lipid profiles were assayed by ultracentrifugation with direct
measurement of LDL by the Genzyme assay on those with
available serum samples. The calculated LDL by the Friedewald
equation was done on the same samples utilizing the values from the ultracentrifugation
assay.
Results: In subjects with TG <400 mg/dL (n =271), 90% of the Genzyme LDL values and Friedewald
calculations were within 30 mg/dL and 32 mg/dL of the ultracentrifugation values, respectively. Of the
observations, 59.8% were within 15 mg/dL of
ultracentrifugation LDL values for Genzyme and 55.2%
for Friedewald. Conversely, in subjects with a TG
>400 mg/dL (n
= 186), 90% of the observations were within 68 mg/dL
of the ultracentrifugation results for the Genzyme
assay compared with 200 mg/dL for Friedewald.
Only 27% of the observations were within 15 mg/dL of
ultracentrifugation LDL values for Genzyme and 16.3%
for Friedewald.
Conclusions: The Genzyme direct LDL assay and the
calculated LDL values determined by the Friedewald equation did not display
adequate agreement with the reference ultracentrifugation LDL method (defined
as being within 15 mg/dL 90% of the time). Use of the
Genzyme direct LDL assay appears to provide little
benefit over that of using the Friedewald equation in
measuring LDL in HIV-infected subjects regardless of TG level.
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