Davis's Lab & Diagnostic Tests

Cholesterol, HDL and LDL

General

Synonym/Acronym:
α1-Lipoprotein cholesterol, high-density cholesterol, HDLC, and β-lipoprotein cholesterol, low-density cholesterol, LDLC.

Common Use:
To assess risk and monitor for coronary artery disease.

Specimen:
Serum (2 mL) collected in a red- or tiger-top tube.

Normal Findings:
(Method: Spectrophotometry)

HDLCConventional UnitsSI Units (Conventional Units × 0.0259)
Birth6–56 mg/dL0.16–1.45 mmol/L
Children, adults, and older adults
DesirableGreater than 60 mg/dLGreater than 1.56 mmol/L
Acceptable40–60 mg/dL0.9–1.56 mmol/L
LowLess than 40 mg/dLLess than 0.9 mmol/L
LDLCConventional UnitsSI Units (Conventional Units × 0.0259)
OptimalLess than 100 mg/dLLess than 2.59 mmol/L
Near optimal100–129 mg/dL2.59–3.34 mmol/L
Borderline high130–159 mg/dL3.37–4.11 mmol/L
High160–189 mg/dL4.14–4.90 mmol/L
Very highGreater than 190 mg/dLGreater than 4.92 mmol/L
NMR LDLC Particle NumberNMR LDLC Small Particle Size
High-risk CADLess than 1,000 nmol/LLess than 850 nmol/L
Moderately high-risk CADLess than 1,300 nmol/LLess than 850 nmol/L
CAD, coronary artery disease; NMR = nuclear magnetic resonance.

Description

High-density lipoprotein cholesterol (HDLC) and low-density lipoprotein cholesterol (LDLC) are the major transport proteins for cholesterol in the body. It is believed that HDLC may have protective properties in that its role includes transporting cholesterol from the arteries to the liver. LDLC is the major transport protein for cholesterol to the arteries from the liver. LDLC can be calculated using total cholesterol, total triglycerides, and HDLC levels. Beyond the total cholesterol, HDL and LDL cholesterol values, other important risk factors must be considered. The Framingham algorithm can assist in estimating the risk of developing coronary artery disease (CAD) within a 10-yr period. The National Cholesterol Education Program (NCEP) also provides important guidelines. The latest NCEP guidelines for target lipid levels, major risk factors, and therapeutic interventions are outlined in Adult Treatment Panel III (ATP III) (www.nhlbi.nih.gov/guidelines/cholesterol/index.htm).

Studies have shown that CAD is inversely related to LDLC particle number and size. The nuclear magnetic resonance (NMR) lipid profile uses NMR imaging spectroscopy to determine LDLC particle number and size in addition to measurement of the traditional lipid markers.

HDLC levels less than 40 mg/dL in men and women represent a coronary risk factor. There is an inverse relationship between HDLC and risk of CAD (i.e., lower HDLC levels represent a higher risk of CAD). Levels of LDLC in terms of risk for CAD are directly proportional to risk and vary by age group. The LDLC can be estimated using the Friedewald formula:

LDLC = (Total Cholesterol) − (HDLC) − (VLDLC)

Very-low-density lipoprotein cholesterol (VLDLC) is estimated by dividing the triglycerides (conventional units) by 5. Triglycerides in SI units would be divided by 2.18 to estimate VLDLC. It is important to note that the formula is valid only if the triglycerides are less than 400 mg/dL or 4.52 mmol/L.

Indications

  • Determine the risk of cardiovascular disease
  • Evaluate the response to dietary and drug therapy for hypercholesterolemia
  • Investigate hypercholesterolemia in light of family history of cardiovascular disease

Potential Diagnosis

Although the exact pathophysiology is unknown, cholesterol is required for many functions at the cellular and organ levels. Elevations of cholesterol are associated with conditions caused by an inherited defect in lipoprotein metabolism, liver disease, kidney disease, or a disorder of the endocrine system. Decreases in cholesterol levels are associated with conditions caused by enzyme deficiencies, malnutrition, malabsorption, liver disease, and sudden increased utilization.

HDLC increased in

  • Alcoholism
  • Biliary cirrhosis
  • Chronic hepatitis
  • Exercise
  • Familial hyper-α-lipoproteinemia

HDLC decreased in

  • Abetalipoproteinemia
  • Cholestasis
  • Chronic renal failure
  • Fish-eye disease
  • Genetic predisposition or enzyme/cofactor deficiency
  • Hepatocellular disorders
  • Hypertriglyceridemia
  • Nephrotic syndrome
  • Obesity
  • Premature CAD
  • Sedentary lifestyle
  • Smoking
  • Tangier’s disease
  • Syndrome X (metabolic syndrome)
  • Uncontrolled diabetes

LDLC increased in

  • Anorexia nervosa
  • Chronic renal failure
  • Corneal arcus
  • Cushing’s syndrome
  • Diabetes
  • Diet high in cholesterol and saturated fat
  • Dysglobulinemias
  • Hepatic disease
  • Hepatic obstruction
  • Hyperlipoproteinemia types IIA and IIB
  • Hypothyroidism
  • Nephrotic syndrome
  • Porphyria
  • Pregnancy
  • Premature CAD
  • Syndrome X (metabolic syndrome)
  • Tendon and tuberous xanthomas

LDLC decreased in

  • Acute stress (severe burns, illness)
  • Chronic anemias
  • Chronic pulmonary disease
  • Genetic predisposition or enzyme/cofactor deficiency
  • Hyperthyroidism
  • Hypolipoproteinemia and abetalipoproteinemia
  • Inflammatory joint disease
  • Myeloma
  • Reye’s syndrome
  • Severe hepatocellular destruction or disease
  • Tangier disease

Critical Findings

N/A

Interfering Factors

  • Drugs that may increase HDLC levels include albuterol, anticonvulsants, cholestyramine, cimetidine, clofibrate and other fibric acid derivatives, estrogens, ethanol (moderate use), lovastatin, niacin, oral contraceptives, pindolol, pravastatin, prazosin, and simvastatin.
  • Drugs that may decrease HDLC levels include acebutolol, atenolol, danazol, diuretics, etretinate, interferon, isotretinoin, linseed oil, metoprolol, neomycin, nonselective β-adrenergic blocking agents, probucol, progesterone, steroids, and thiazides.
  • Drugs that may increase LDLC levels include androgens, catecholamines, chenodiol, cyclosporine, danazol, diuretics, etretinate, glucogenic corticosteroids, and progestins.
  • Drugs that may decrease LDLC levels include aminosalicylic acid, cholestyramine, colestipol, estrogens, fibric acid derivatives, interferon, lovastatin, neomycin, niacin, pravastatin, prazosin, probucol, simvastatin, terazosin, and thyroxine.
  • Some of the drugs used to lower total cholesterol and LDLC or increase HDLC may cause liver damage.
  • Grossly elevated triglyceride levels invalidate the Friedewald formula for mathematical estimation of LDLC; if the triglyceride level is greater than 400 mg/dL, the formula should not be used.
  • Fasting before specimen collection is highly recommended. Ideally, the patient should be on a stable diet for 3 wk and fast for 12 hr before specimen collection.
  • Failure to follow dietary restrictions before the procedure may cause the procedure to be canceled or repeated.

Nursing Implications Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist with evaluation of cholesterol level.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s cardiovascular system and results of previously performed laboratory tests and diagnostic and surgical procedures. The presence of other risk factors, such as family history of heart disease, smoking, obesity, diet, lack of physical activity, hypertension, diabetes, previous myocardial infarction, and previous vascular disease, should be investigated.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Instruct the patient to fast for 12 hr before specimen collection. Protocols may vary among facilities.
  • Confirm with the requesting health-care provider (HCP) that the patient should withhold medications known to influence test results, and instruct the patient accordingly.
  • There are no fluid restrictions unless by medical direction.

Intratest

  • Ensure that the patient has complied with dietary and medication restrictions as well as other pretesting preparations; ensure that food has been restricted for at least 12 hr prior to the procedure.
  • If the patient has a history of allergic reaction to latex, avoid the use of equipment containing latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.

Post Test

  • A report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Instruct the patient to resume usual diet, fluids, and medications, as directed by the HCP.
  • Nutritional Considerations: Decreased HDLC level and increased LDLC level may be associated with CAD. Nutritional therapy is recommended for the patient identified to be at high risk for developing CAD. The American Heart Association and National Heart, Lung, and Blood Institute (NHLBI) recommend nutritional therapy for individuals identified to be at high risk for developing CAD or individuals who have specific risk factors and/or existing medical conditions (e.g., elevated LDL cholesterol levels, other lipid disorders, insulin-dependent diabetes, insulin resistance, or metabolic syndrome). If overweight, the patient should be encouraged to achieve a normal weight. Guidelines for the Therapeutic Lifestyle Changes (TLC) diet are outlined in the Third Report of the Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III [ATP III]). The TLC diet emphasizes a reduction in foods high in saturated fats and cholesterol. Red meats, eggs, and dairy products are the major sources of saturated fats and cholesterol. If triglycerides also are elevated, the patient should be advised to eliminate or reduce alcohol and simple carbohydrates from the diet. The TLC approach also includes the use of plant stanols or sterols and increased dissolved fiber as an option for lowering LDL cholesterol levels; nutritional recommendations for daily total caloric intake; recommendations for allowable percentage of calories derived from fat (saturated and unsaturated), carbohydrates, protein, and cholesterol; as well as recommendations for daily expenditure of energy.
  • Nutritional Considerations: Overweight patients with high blood pressure should be encouraged to achieve a normal weight. Other changeable risk factors warranting patient education include strategies to safely decrease sodium intake, increase physical activity, decrease alcohol consumption, eliminate tobacco use, and decrease cholesterol levels.
  • Social and Cultural Considerations: Numerous studies point to the prevalence of excess body weight in American children and adolescents. Experts estimate that obesity is present in 25% of the population ages 6 to 11 yr. The medical, social, and emotional consequences of excess body weight are significant. Special attention should be given to instructing the child and caregiver regarding health risks and weight-control education.
  • Recognize anxiety related to test results, and be supportive of fear of shortened life expectancy. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate. Educate the patient regarding access to counseling services. Provide contact information, if desired, for the American Heart Association (www.americanheart.org) or the NHLBI (www.nhlbi.nih.gov).
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

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