LDL cholesterol is a calculated parameter that gives an estimate of the proportion of the total plasma cholesterol that is present as low-density lipoprotein (LDL).
LDL particles are cholesterol-rich lipoproteins with atherogenic potential.
LDL concentration correlates with cardiovascular risk- a relationship that has also been shown to be causative.
LDL Cholesterol (Calculated)
There is no single LDL value above which lipid-lowering therapy is indicated. Instead, LDL cholesterol may be combined with other cardiovascular risk factors to estimate the overall cardiovascular risk for an individual using risk-prediction algorithms (some algorithms use the total/HDL cholesterol ratio in preference to LDL cholesterol). Treatment decisions should be made based on this overall risk.
LDL cholesterol is measured to monitor the effectiveness of lipid-lowering therapy. Different treatment targets have been published. In NZ, the Ministry of Health guidelines recommend that an LDL of <1.8mmol/L should be targeted for high-risk individuals (5 year overall CVD risk >15%), with a minimum 40% reduction in LDL cholesterol recommended for lower-risk patients. However it should be noted that there is a continuum of risk reduction with LDL reduction (i.e. the lower the LDL, the lower the overall risk) therefore some individuals may wish to target lower LDL levels.
Familial hypercholesterolaemia (FH) is an autosomal dominant inherited condition that occurs due to a mutation in one of the genes associated with LDL particle clearance (usually the LDL receptor). Patients with FH have a high risk of premature cardiovascular disease and benefit from lifelong lipid-lowering therapy. FH should be suspected in those with a particularly high LDL cholesterol (e.g. >5.0mmol/L), especially if there is a family history of premature dyslipidaemia or cardiovascular disease. More information on FH can be found on the website of the FH Australasia Network.
LDL is a calculated test (see test method section below). The equation used to calculate LDL does not perform well in the presence of elevated triglycerides. Therefore an LDL result will not be calculated if the triglyceride concentration is >4.5mmol/L. LDL can be measured by ultracentrifugation in these cases, if required.
Diagnosis of dyslipidaemia
See above. No reference interval applies for LDL but the result should be combined with other risk factors to calculate the patient’s overall cardiovascular risk.
Monitoring lipid lowering therapy (From NZ Ministry of Health)
|Risk group||Target LDL cholesterol|
|High (5-year CVD risk >15%)||<1.8mmol/L|
|Low/moderate||>40% reduction from baseline|
|Familial hypercholesterolaemia||Seek specialist advice|
Diagnosis of FH
Consider FH in individuals with particularly high LDL cholesterol (in the absence of secondary causes of dyslipidaemia) and in those with a personal or family history of premature cardiovascular disease. See https://www.athero.org.au/fh/health-professionals/how-to-diagnose-fh/ for more information on diagnosis.
Calculated test using the Friedewald formula
LDLC = Total cholesterol - HDL cholesterol - (Triglycerides/2.2)
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