Sixty percent to 70% of the total serum cholesterol is present as LDL. LDLs are the cholesterol-rich remnants of the VLDL lipid transport vehicle. Because LDL has a longer half-life (3–4 days) than its precursor VLDL, LDL is more prevalent in the blood. It is mainly catabolized in the liver and possibly in nonhepatic cells as well. The VLDLs are major carriers of triglycerides. Degradation of VLDL is a major source of LDL. Circulating fatty acids form triglycerides in the liver, and these are packaged with apoprotein and cholesterol to be exported into the blood as VLDLs. Recently, studies have shown that not only is the amount of cholesterol present in LDL of importance but also of importance are the number of LDL particles (LDL-P). It has been shown that the higher the number of LDL particles, the higher is the risk for heart disease.

This test is specifically done to determine CAD risk. LDL, “the bad cholesterol,” is closely associated with increased incidence of atherosclerosis and CAD. The test of choice is LDL because it has a longer half-life and it is easier to measure.

LDL-C:

Adults:

• Optimal: <100 mg/dL or <2.6 mmol/L

• Near optimal: 100–129 mg/dL or 2.6–3.3 mmol/L

• Borderline high: 130–159 mg/dL or 3.4–4.1 mmol/L

• High: 160–189 mg/dL or 4.2–4.9 mmol/L

• Very high: ≥190 mg/dL or ≥5.0 mmol/L

Children and adolescents:

• Desirable: <110 mg/dL or <2.8 mmol/L

• Borderline high risk: 110–129 mg/dL or 2.8–3.4 mmol/L

• High risk: >130 mg/dL or >3.4 mmol/L

LDL-P:

• Optimal: <1000 nmol/L

• Borderline: 1300–1600 nmol/L

• High risk: >1600 nmol/L

• Very high risk: >2000 nmol/L

VLDL-C:

• <30 mg/dL (calculated)

1. Use the following equation for VLDL calculation (estimation): triglycerides ÷ 5.

2. Calculate LDL-C levels by using Friedwald formula:

   

3. The formula is valid only if the cholesterol and triglyceride values are from a fasting specimen and the triglyceride value is >400 mg/dL or >10.4 mmol/L.

4. Lipoprotein analysis measures fasting levels of total cholesterol, total triglycerides, and HDL-C. Calculate LDL-C from these values.

5. There is a direct test for LDL that may be ordered if triglycerides are >400 mg/dL or >10.4 mmol/L.

1. Increased LDL levels are caused by the following conditions:

   1. Familial type II hyperlipidemia, familial hypercholesterolemia

   2. Secondary causes include the following:

      1. Diet high in cholesterol and saturated fat

      2. Hyperlipidemia secondary to hypothyroidism

      3. Nephrotic syndrome

      4. Multiple myeloma and other dysglobulinemias

      5. Hepatic obstruction or disease

      6. Anorexia nervosa

      7. Diabetes

      8. CKD

      9. Porphyria (inherited or acquired disorders of certain enzymes that affect the nervous system)

      10. Premature CHD

2. Decreased LDL levels occur in the following conditions:

   1. Hypolipoproteinemia

   2. Tangier disease (autosomal recessive disease resulting in low levels of HDL-C and accumulation of cholesterol)

   3. Type I hyperlipidemia

   4. Apolipoprotein C-II deficiency

   5. Hyperthyroidism

   6. Chronic anemias

   7. Severe hepatocellular disease

   8. Reye syndrome

   9. Acute stress (burns, illness)

   10. Inflammatory joint disease

   11. Chronic pulmonary disease

Pretest Patient Care

1. Explain test purpose. A 9- to 12-hour fast is recommended. Alcohol should not be consumed for at least 24 hours before test.

2. The patient should ideally be on a stable diet for 3 weeks.

3. If possible, withhold all medication for at least 24 hours before testing. Check with the healthcare provider.

4. Encourage relaxation.

5. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.