Cholesterol (HDL and LDL)

Keywords: HDL, HDLC HDL-C, High density lipoprotein cholesterol, LDL, LDLC, LDL-C, Low density lipoprotein cholesterol

Specimen:

5 mL blood in EDTA, lithium heparin or plain tube (same specimen as for total cholesterol will suffice).

Prolonged tourniquet use can artefactually increase levels by up to 20%.

See Table 1.

Method:

Numerous separation methods are available, including direct spectrophotometric assay or ultracentrifugation and electrophoresis.

LDL cholesterol is usually calculated rather than measured directly although this is unreliable if levels of triglyceride are > 4.5 mmol/L.

The usual calculation using mmol/L for LDL cholesterol (Friedewald equation) is:

LDL cholesterol = total cholesterol - HDL cholesterol - triglyceride/2.2

Reference Interval:

HDL cholesterol

Female:

Population reference interval: 1.0-2.2 mmol/L

Therapeutic targets: > 1.0 mmol/L

Male:

Population reference interval: 0.9-2.0 mmol/L

Therapeutic targets: > 1.0 mmol/L

LDL cholesterol

Population reference interval: 2.0-3.4 mmol/L

Therapeutic targets: < 2.5 mmol/L (depends on risk, refer to www.cvdcheck.org.au).

Application:

Investigation of lipid status in suspected Hyperlipidaemia.

Assessment of risk for atherosclerosis, especially coronary artery disease.

Interpretation:

Low levels of HDL cholesterol and high levels of LDL cholesterol are associated with an increased risk of atherosclerotic vascular disease.

National guidelines generally specify specific targets, refer to www.cvdcheck.org.au.

LDL levels are reduced for up to 8 weeks with acute illness (eg, Myocardial infarction, acute infection) and assays should not be performed during this time.

See also Apolipoprotein.

Reference:

Linton M.Fand Fazio S. Am J Cardiol 2003; 92(1A): 19i-26i.

National Vascular Disease Prevention Alliance: www.cvdcheck.org.au