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- High-density Lipoprotein Particle Number, Total
HDL-P, a measurement of total HDL particle number concentration, may be a better marker of residual risk than chemically measured high-density lipoprotein cholesterol (HDL-C, the so-called “good” cholesterol) or apolipoprotein A-1 (apoA-1, the major protein on HDL), ie, there may be a more consistent inverse association between cardiovascular endpoints and HDL-P compared with HDL-C.
Direct quantification of HDL-P concentration by NMR may be useful to refine cardiovascular risk and to evaluate novel HDL-directed therapies. Further studies are needed to clarify the role of HDL-P in clinical practice.
This test was developed, and its performance characteristics determined, by LabCorp. It has not been cleared or approved by the US Food and Drug Administration (FDA).
Nuclear magnetic resonance (NMR)
Spun NMR LipoTube (preferred), serum from a plain red-top tube, plasma from a lavender-top (EDTA-no gel), or green-top (heparin-no gel) tube. Keep refrigerated and ship with frozen cool packs.
Collect specimen in NMR LipoTube (black-and-yellow-top tube), which is the preferred container. Plain red-top, green-top (heparin-no gel), or lavender-top (EDTA-no gel) tubes are also acceptable. Serum or plasma drawn in gel-barrier collection tubes other than the NMR LipoTube should not be used. The LipoTube is the only acceptable gel-barrier tube. Gently invert tube 8 to 10 times to mix contents and allow specimen to clot for 30 minutes upright at room temperature prior to centrifugation (Plasma tubes should not clot). Centrifuge specimen within two hours of collection at 1800xg for 10 to 15 minutes to separate serum/plasma from the red cells and to avoid red cell contamination during shipment. If the sample cannot be centrifuged immediately, the sample should be refrigerated (at 2ºC to 8ºC) and centrifuged within 24 hours of collection. Note: Centrifuging the specimen while still cold may negatively affect the migration of the gel to the serum/red cell interface and may increase the likelihood of specimens being contaminated with red cells during shipment. All specimens should be centrifuged by the client, prior to shipment to LabCorp, to ensure sample integrity. Do not open NMR LipoTube (black-and-yellow-top). Immediately after centrifugation, pipette separated red-top serum or green-top/lavender-top plasma into a transport tube and label accordingly (serum, heparin plasma, EDTA plasma). Keep samples refrigerated until shipment to the laboratory, and ship with frozen cool packs.
Refrigerate all acceptable tube types as soon as possible after centrifugation and within 24 hours of collection. Keep refrigerated prior to shipment, and ship on frozen cool packs. Do not store at room temperature. Do not freeze the sample. Sample is stable refrigerated for 14 days.
Causes for Rejection
Unspun specimens; plasma/serum contaminated with red cells; citrated plasma (light blue-top tube); gross hemolysis; specimen received in inappropriate container; specimen stored at room temperature for more than a total preanalytical time of 30 hours; specimen more than 14 days old