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Chemistry

Result Interpretation

Accurate interpretation of lipid test results is crucial for assessing cardiovascular risk and guiding patient management

  • Key Analytes
    • Total Cholesterol (TC)
    • Triglycerides (TG)
    • High-Density Lipoprotein Cholesterol (HDL-C)
    • Low-Density Lipoprotein Cholesterol (LDL-C)
  • Additional Analytes
    • Non-HDL Cholesterol
    • Apolipoproteins (Apo A-1, Apo B)
    • Lipoprotein (a) [Lp(a)]

Total Cholesterol

  • Reference Interval: < 200 mg/dL (5.18 mmol/L)
  • Interpretation
    • Desirable: < 200 mg/dL
    • Borderline High: 200-239 mg/dL (5.18-6.18 mmol/L)
    • High: ≥ 240 mg/dL (6.22 mmol/L)
  • Clinical Significance
    • Elevated TC is associated with an increased risk of cardiovascular disease (CVD)
    • TC is a component of the LDL-C calculation and contributes to overall risk assessment

Triglycerides

  • Reference Interval: < 150 mg/dL (1.7 mmol/L)
  • Interpretation
    • Normal: < 150 mg/dL
    • Borderline High: 150-199 mg/dL (1.7-2.2 mmol/L)
    • High: 200-499 mg/dL (2.3-5.6 mmol/L)
    • Very High: ≥ 500 mg/dL (5.7 mmol/L)
  • Clinical Significance
    • Elevated TG is associated with increased risk of CVD, especially in the presence of low HDL-C and other risk factors
    • Very high TG levels (> 500 mg/dL) increase the risk of pancreatitis
    • TG is a component of the LDL-C calculation (when using Friedewald equation)

High-Density Lipoprotein Cholesterol

  • Reference Interval: > 40 mg/dL (1.0 mmol/L)
  • Interpretation
    • Low: < 40 mg/dL
    • Optimal: ≥ 60 mg/dL (1.55 mmol/L)
  • Clinical Significance
    • Low HDL-C is an independent risk factor for CVD
    • High HDL-C is considered protective against CVD
    • HDL-C is a component of the LDL-C calculation

Low-Density Lipoprotein Cholesterol

  • Reference Interval: Varies depending on individual risk factors
  • Interpretation (ATP III Guidelines)
    • Optimal: < 100 mg/dL (2.59 mmol/L)
    • Near Optimal: 100-129 mg/dL (2.59-3.34 mmol/L)
    • Borderline High: 130-159 mg/dL (3.37-4.11 mmol/L)
    • High: 160-189 mg/dL (4.14-4.89 mmol/L)
    • Very High: ≥ 190 mg/dL (4.91 mmol/L)
  • Clinical Significance
    • LDL-C is the primary target of cholesterol-lowering therapy
    • Lower LDL-C levels are associated with reduced risk of CVD events
    • LDL-C goals are individualized based on the patient’s overall CVD risk

Non-HDL Cholesterol

  • Calculation: Non-HDL-C = Total Cholesterol - HDL-C
  • Interpretation
    • Desirable: < 130 mg/dL (3.37 mmol/L)
    • Borderline High: 130-159 mg/dL (3.37-4.11 mmol/L)
    • High: 160-189 mg/dL (4.14-4.89 mmol/L)
    • Very High: ≥ 190 mg/dL (4.91 mmol/L)
  • Clinical Significance
    • Non-HDL-C includes all atherogenic lipoproteins (LDL, VLDL, IDL, Lp(a))
    • It may be a better predictor of CVD risk than LDL-C alone, especially in patients with high triglycerides

Apolipoproteins

  • Apo A-1 (Major protein of HDL)
    • Reference Interval:
      • Males: 100-160 mg/dL
      • Females: 120-190 mg/dL
    • Clinical Significance:
      • Low levels are associated with increased CVD risk
  • Apo B (Major protein of LDL, VLDL, IDL, and Lp(a))
    • Reference Interval: 80-130 mg/dL
    • Clinical Significance:
      • High levels are associated with increased CVD risk
      • May be a better predictor of CVD risk than LDL-C alone, especially in patients with metabolic syndrome or diabetes

Lipoprotein (a)

  • Reference Interval: < 30 mg/dL or < 75 nmol/L
  • Clinical Significance
    • Elevated Lp(a) is an independent risk factor for CVD
    • Lp(a) levels are largely genetically determined and less responsive to lifestyle modifications
    • Consider measuring Lp(a) in patients with premature CVD or a family history of CVD

Factors Affecting Interpretation

  • Fasting Status: Triglyceride levels are significantly affected by fasting status. Non-fasting samples can lead to falsely elevated triglyceride levels
  • Medications: Certain medications can affect lipid levels (e.g., statins, fibrates, niacin, beta-blockers, oral contraceptives, corticosteroids)
  • Medical Conditions: Certain medical conditions can affect lipid levels (e.g., diabetes, hypothyroidism, kidney disease, liver disease, metabolic syndrome)
  • Acute Illness/Stress: Acute illness, surgery, or trauma can affect lipid levels
  • Ethnicity: Certain ethnic groups may have different lipid levels compared to Caucasians
  • Age and Gender: Lipid levels vary with age and gender
  • Pregnancy: Pregnancy affects lipid metabolism, and specific reference intervals are used for pregnant women

Key Terms

  • Total Cholesterol (TC): A measure of all cholesterol in the blood
  • Triglycerides (TG): A type of fat in the blood
  • High-Density Lipoprotein Cholesterol (HDL-C): “Good” cholesterol that helps remove LDL from the arteries
  • Low-Density Lipoprotein Cholesterol (LDL-C): “Bad” cholesterol that contributes to plaque buildup
  • Non-HDL Cholesterol: Total cholesterol minus HDL cholesterol, representing all atherogenic lipoproteins
  • Apolipoproteins (Apo A-1, Apo B): Proteins that bind to lipoproteins
  • Lipoprotein (a) [Lp(a)]: A lipoprotein particle associated with increased CVD risk
  • Atherosclerosis: Plaque buildup in arteries
  • Cardiovascular Disease (CVD): Diseases of the heart and blood vessels
  • Familial Hypercholesterolemia (FH): A genetic disorder characterized by high LDL-C levels
  • Familial Hypertriglyceridemia (FHTG): A genetic disorder characterized by elevated triglyceride levels
  • Metabolic Syndrome: A cluster of conditions that increase the risk of heart disease, stroke, and diabetes
  • Statin Therapy: Medications that lower LDL cholesterol levels
  • Fibrates: Medications that lower triglyceride levels and increase HDL cholesterol levels