Background:
The Department of Pathology & Laboratory Medicine will introduce new tests for Lipoprotein(a), and direct low-density lipoprotein cholesterol (LDL-C).
The new Lipoprotein(a) assay (test code: LPACH) will replace the existing Lipoprotein(a) cholesterol assay. The new assay is traceable to WHO-IFCC Reference Material SRM2B (1). Values will be reported in units of nmol/L, and conversion to mg/dL is not recommended (2). An optimal level is less than 75 nmol/L, and a value of 125 nmol/L or greater may be considered a risk enhancing factor (2, 3).
Direct LDL-C (test code: LDLD) offers an alternative to calculated LDL-C. In hypertriglyceridemia, values of LDL-C calculated by the Friedwald equation may be less accurate, particularly when LDL-C is < 70 mg/dL. The new direct LDL-C assay is a two-phase homogenous enzymatic assay utilizing selective solubilization of lipoprotein particles (4). Population studies suggest that an optimal LDL-C level is < 100 mg/dL; however, lower levels may be desirable in patients with increased atherosclerotic cardiovascular disease risk (3). A value of 190 mg/dL or greater is severe hypercholesterolemia and may indicate familial hypercholesterolemia (3).
Effective date: April 7, 2021
Specimen requirement and testing information:
Specimen: Collect 4.0 mL blood in a light green (lithium heparin), gold, or red top tube. Spin down and separate plasma or serum from cells as soon as possible, and within 2 hours of sample collection.
Test methodology: Direct LDL-C: enzymatic; Lp(a): immunoturbidimetric
Test codes: LPACH, LDLD
Stability:
Plasma or serum, after separation from cells:
Ambient: NA
Refrigerated: Direct LDL-C: 5 days; Lp(a): 14 days.
Frozen: For long term storage, temperature of -70˚C is recommended. Thaw only once.
Turnaround time (TAT):
STAT: NA
Routine: Direct LDL-C: 2-4 hours; Lp(a): 1-3 days
Set Up Days: Direct LDL-C: Daily; Lp(a): M, W, F
Specimen required: 2.0 mL plasma
Minimum volume: 0.5 mL plasma
Rejection criteria:
Specimens that exceed stated stability, unlabeled/mislabeled/mismatched specimens, specimens submitted in leaking containers, hemolyzed or lipemic specimens.
References ›
A summary of all tests offered by our laboratory services can be found here: http://www.pathology.uci.edu/services/index.asp
Sincerely,
Bridgit O. Crews, PhD, DABCC
Director
Clinical Chemistry, Toxicology & Point-of-Care Testing
Edwin S. Monuki, MD, PhD
Chair
Department of Pathology & Laboratory Medicine
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