Overview of cholesterol components and laboratory evaluation.

Hyperlipidemia is defined as an increase in one or more of the components of cholesterol (total cholesterol, triglycerides, LDL, VLDL, and HDL). LDL (low density lipoprotein) is the bad cholesterol, which is carried away from the liver and deposited in the arteries (among other places). HDL (high density lipoprotein) is the good cholesterol, which carries excess cholesterol back to the liver, where it can be metabolized and eliminated from the body. High cholesterol levels can result in the development of coronary artery disease (CAD). CAD occurs as a result of cholesterol depositing in the arteries, which eventually results in plaque formation. These plaques narrow the diameter of the arteries and compromise blood flow. The table below illustrates the various components of cholesterol and how these levels correlate with the risk for development of CAD.

	LDL (mg/dL)	HDL (mg/dL)	Total cholesterol (mg/dL)	Triglycerides (mg/dL)	LDL/HDL Ratio
Desired level (low risk)	<130	>60	<200	<200	0.5-3.0
Borderline level (moderate risk)	130-159	35-60	200-239	200-400	3.0-6.0
Elevated level (high risk)	³ 160	<35	>240	>400	>6.0

Simple cholesterol measurements may be obtained from blood via a finger stick or a venopuncture . These simple serum lipid panels are quick and easy to obtain and are used to determine total cholesterol (TC), HDL and triglycerides. From this measurement, a TC/HDL ratio can be calculated and used to determine risk for developing consequent CAD.

The TC/HDL ratio is defined as:

Low risk 3.3-4.4

Average risk 4.4-7.1

Moderate risk 7.1-11.0

High risk >11.0

Another ratio that is helpful in determining risk for developing subsequent CAD is the LDL/HDL ratio. Unlike the TC/HDL ratio, which can be obtained directly from the lipid panel, determination of the LDL/HDL ratio requires calculation of the LDL. However, in order to calculate the LDL, the VLDL must be calculated first. Using the TC, HDL, and triglyceride levels available from laboratory tests, the following equations enable calculation of the VLDL and LDL.

VLDL Calculation: VLDL = Triglycerides divided by 5 (TG/5)

****If TG > 400, calculation is not accurate

LDL Calculation: LDL = TC – (VLDL + HDL)

In addition to increased levels of cholesterol and its components, other risk factors (both positive and negative) are associated with the development of CAD. Positive risk factors increase your risk for developing CAD, whereas negative risk factors actually decrease your risk for developing CAD.

Positive Risk Factors

• Age (men >45 years; women >55 years or premature menopause without estrogen therapy
• Family history (definite heart attack or sudden death before 55 years in father or before 65 years in mother)
• Current cigarette smoking
• High blood pressure (>140/90 mm Hg or on blood pressure medication)
• Low HDL (<35 MG/dL)
• Diabetes mellitus

Negative Risk Factors

• Increased HDL (>60 mg/dL)

References:

1. Wallach, Jacques. Interpretation of Diagnostic Test. 6^th edition. 477-85.
2. Dipiro, et al. Pharmacotherapy: A Pathophysiologic Approach. 4^th edition.