Chemistry, toxicology & urinalysis

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Metabolism

Lipid panel



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PubMed Search: Lipid panel[title]

Archana Shetty, M.B.B.S., M.D.
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Cite this page: Shetty A. Lipid panel. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/chemistrylipidpanel.html. Accessed December 6th, 2022.
Definition / general
  • Set of chemistry tests to measure the level of various fats in a person's blood
Essential features
  • Typical lipid profile includes testing for total cholesterol, high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), triglycerides (TG), very low density lipoprotein cholesterol (VLDL-C) and non-HDL cholesterol
  • Maintaining desirable concentrations of each lipid lowers the risk of heart attack and stroke
Terminology
  • Lipid profile
  • Complete cholesterol test
  • Lipoproteins
Indications for testing
  • Known risk factors for developing heart disease (e.g., cigarette smoking, history of heart disease or atherosclerosis, history of stroke or heart attack)
  • Family history of heart disease
  • High blood pressure
  • Obesity (Mayo Clin Proc Innov Qual Outcomes 2019;3:251)
  • As a part of routine health check up, a fasting or nonfasting lipoprotein profile should be obtained at least every 5 years in all adults (≥ 20 years of age)
  • Current guidelines from the National Heart, Lung, and Blood Institute recommend that children aged 9 - 11 years of age and young adults 17 - 21 years of age be screened for high cholesterol, regardless of risk factors
Laboratory
  • Specimen for testing: serum (blood sample)
    • Preferred: serum gel barrier tube (gold top)
    • Alternative: plasma separator tube (green top containing sodium heparin or lithium heparin)
  • Collection instructions:
    • Serum gel or plasma separator tube must be centrifuged within 2 hours of draw time
    • Red top tube must be centrifuged and aliquoted within 2 hours of draw time
  • Rejection criteria:
    • Sample showing gross hemolysis
    • Underfilled or overfilled tube
    • Anticoagulants other than heparin
  • Possible interferences:
    • Lipemic and icteric samples
    • Plasma mixed with anticoagulants, such as oxalates, citrates and fluoride
  • Methodology:
    • Spectrophotometric (colorimetric)
  • Variations:
    • Change from an upright to a supine position due to dilutional effect can reduce the cholesterol levels by 10% and triglycerides by 12%
    • Prolonged tourniquet application (2 - 5 minutes) can increase cholesterol by 5 - 15%
    • Cholesterol is slightly higher in winter than in summer and the opposite is true for triglycerides
  • Timing of test:
    • Sample drawn after overnight fasting of 12 hours
    • Though a fasting sample is preferred, recent guidelines recommend measurement of nonfasting lipids may be an equivalent or better predictor of cardiovascular conditions as nonfasting lipid profiles can reflect real status of circulating lipids (Ann Transl Med 2021;9:386)
  • Principle:
    • Cholesterol and triglycerides measured using enzymatically coupled reactions
    • HDL: measured directly
    • LDL: calculated / measured directly
    • VLDL: calculated
Lipid types
  • Total cholesterol:
    • Lipids are synthesized by the body and transported by 5 classes of lipoproteins (HDL, LDL, VLDL, chylomicrons and IDL)
    • Cholesterol is insoluble and requires transporters (e.g., lipoproteins)
    • HDL and LDL play contradictory roles in cholesterol metabolism
    • Total cholesterol by itself has a low, predictive value with regard to coronary artery disease (CAD); it provides only a baseline value to decide if further investigation of lipid metabolism must be carried out
    • Since lipids cannot dissolve in water, they need to be broken down for ease of transportation in blood; proteins that aid in this process are lipoproteins (HDL and LDL)
  • Triglycerides:
    • Fatty acids complexed with glycerol, which represent the storage form of fat that can be used later as an energy source
    • Ideal levels are < 150 mg/dL
    • Independent risk factor for peripheral vascular disease and ischemic heart disease (IHD)
    • Elevated in patients with acute and chronic pancreatitis, diabetes mellitus, diseases of lipid metabolism, endocrine and chronic inflammatory diseases (e.g., rheumatoid arthritis, systemic lupus erythematosus) (NCBI Bookshelf: Endotext [Accessed 23 February 2022])
    • Levels can help to classify various lipoprotein disorders and in the assessment of risk factors for atherosclerosis and coronary artery disease (CAD)
  • HDL cholesterol:
    • Also called good cholesterol or atheroprotective cholesterol
    • Preferred levels > 40 mg/dL in men and > 50 mg/dL in women
    • Type of lipoprotein that absorbs cholesterol and carries it back to the liver, for elimination from the body (Sports Med 2014;44:211)
    • Levels are inversely associated with incidence of CAD
    • Levels are used for early recognition of atherosclerosis risk and for monitoring patients when on lipid lowering medications
  • LDL cholesterol:
    • Also called bad cholesterol as it transports cholesterol from liver to peripheral tissues
    • Preferred levels < 130 mg/dL
    • High levels of LDL cholesterol increase risk for heart disease and stroke by accumulating on the walls of blood vessels (J Clin Lipidol 2014;8:473)
    • Oxidized LDL is found in higher levels in smokers, diabetics and patients with insulin resistance
  • Lipoprotein a (Lp[a]):
    • Similar to LDL but contains an additional protein, apolipoprotein A (apo[a])
    • Not routinely tested for as a part of lipid panel
    • Interferes with plasminogen activation and inhibits fibrinolysis, leading to unopposed intravenous thrombosis and possible myocardial infarction
    • Levels assessed in patients with personal history of (or first degree relative with) premature atherosclerotic vascular disease (particularly if otherwise considered low risk) and in patients with severe hypercholesterolemia (LDL-C ≥ 190 mg/dL) (Curr Atheroscler Rep 2021;23:51)
  • VLDL cholesterol:
    • Type of LDL cholesterol that is synthesized by liver and is mainly a transporter of triglycerides
    • High levels of VLDL cholesterol have been associated with the development of plaque deposits on artery walls, which narrow the passage and restrict blood flow
  • Non-HDL cholesterol:
    • Calculated by subtracting HDL-C value from total cholesterol value
    • Non-HDL-C is used to assess risk of heart disease or to decide on treatment targets for cholesterol lowering drug therapy (Am J Prev Cardiol 2021;6:100174)
Reference ranges
  • Total cholesterol:
    • < 18 years: < 170 mg/dL
    • Adult: see below
  • HDL cholesterol: males ≥ 40 mg/dL; females ≥ 50 mg/dL
  • VLDL cholesterol: 5 - 40 mg/dL
  • Lp(a): < 30 mg/dL
  • Non-HDL cholesterol:
    • < 100 mg/dL target level for high risk cardiovascular disease
    • < 130 mg/dL optimal for general population

Total cholesterol
Desirable Borderline high High
< 200 mg/dL 200 - 239 mg/dL ≥ 240 mg/dL

Triglycerides
Normal Borderline high High Very high
< 150 mg/dL 150 - 199 mg/dL 200 - 499 mg/dL ≥ 500 mg/dL

LDL cholesterol
Desirable Above desirable Borderline high High Very high
< 100 mg/dL 100 - 129 mg/dL 130 - 159 mg/dL 160 - 189 mg/dL ≥ 190 mg/dL

  • Variations:
    • Results for each component of a lipid profile must be interpreted in context with other risk factors, including age, sex, smoking status, family and personal history of heart disease
  • References: Circulation 2019;139:e1046, Circulation 2019;140:e596
Board review style question #1
HDL cholesterol is called the good cholesterol because it

  1. Contains enzymes to break down cholesterol
  2. Is a negative regulator of cholesterol synthesis
  3. Transports cholesterol from liver to tissues for further metabolism
  4. Transports cholesterol from tissues to liver for excretion
Board review style answer #1
D. Transports cholesterol from tissues to liver for excretion

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Reference: Lipid panel
Board review style question #2
The level of which of the following is inversely related to the risk of cardiovascular disease?

  1. High density lipoprotein (HDL)
  2. Intermediate density lipoprotein (IDL)
  3. Low density lipoprotein (LDL)
  4. Very low density lipoprotein (VLDL)
Board review style answer #2
A. High density lipoprotein (HDL)

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Reference: Lipid panel
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