4363.0.55.001 - Australian Health Survey: Users' Guide, 2011-13

ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 11/12/2013

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Contents >> Biomedical Measures >> Cardiovascular disease (CVD) biomarkers >> Low Density Lipoprotein (LDL) cholesterol

LOW DENSITY LIPOPROTEIN (LDL) CHOLESTEROL

Definition

Low Density Lipoprotein (LDL), also known as ‘bad’ cholesterol, can leave fatty deposits in the blood vessels and arteries blocking the passage of blood flow.¹ High levels of LDL cholesterol may increase the risk of cardiovascular disease (CVD).

The LDL cholesterol equation measures the amount of ‘bad’ cholesterol circulating in the blood at the time of the test. LDL cholesterol results were calculated using an equation with fasting total cholesterol, HDL cholesterol and triglyceride test results. LDL cholesterol results were calculated at the Douglass Hanly Moir (DHM) laboratory and provided to the Australian Bureau of Statistics (ABS).

Population

LDL cholesterol results were obtained for persons aged 12 years and over, who agreed to participate in the National Health Measures Survey (NHMS) and who fasted for 8 hours or more, prior to providing a blood sample.

Methodology

LDL cholesterol was calculated from total cholesterol, High Density Lipoprotein (HDL) cholesterol and fasting triglyceride levels using the Friedewald equation³:

LDL cholesterol (mmol/L) = Total cholesterol – HDL cholesterol - Triglyceride/2.2

In the NHMS, cut off reference values for normal and abnormal results were sourced from the 2005 position statement² on lipid management by the National Heart Foundation Australia and the Cardiac Society of Australia and New Zealand (NHFA/CSANZ). These guidelines are based on epidemiological data and publications of major clinical trials.

In the NHMS, the following definitions were used for LDL cholesterol:

Normal LDL cholesterol levels < 3.5 mmol/L
Abnormal LDL cholesterol levels ≥ 3.5 mmol/L.

Further test information about the analysis method and machine used to measure lipid levels is available in Excel spreadsheet format in the Downloads page of this product.

Data items

The data items and related output categories for this topic are available in Excel spreadsheet format from the Downloads page of this product.

Interpretation

Points to be considered when interpreting data for this topic include the following:

LDL cholesterol results do not confirm a specific diagnosis without consultation with a health professional.
Age, gender and taking lipid lowering medications are all variables that may affect lipid and lipoprotein levels.⁴ As a result, the data should be interpreted with care.
There are a number of different test methods for measuring LDL cholesterol, which may produce different results. The data from this topic should therefore be used with caution when comparing LDL cholesterol results from other studies using a different test method or equation.
Only persons who fasted were included into the LDL cholesterol data, as the Friedewald equation required a fasting triglyceride result.
Persons with a triglyceride level of ≥ 4.5 mmol/L were excluded from the LDL cholesterol data. According to Friedewald et al, the inclusion of triglyceride levels ≥ 4.5 mmol/L (400 mg/100 ml) will result in the generation of a false LDL cholesterol result.³
There are a number of different test methods for measuring total and HDL cholesterol and triglycerides, and different LDL equations, which may produce different results. The data from this topic should therefore be used with caution when comparing LDL results from other studies using a different test method or equation.

Comparability with other surveys

The NHMS is the first ABS survey to collect biomedical data on cholesterol levels.

Cholesterol data has been collected in other non-ABS surveys. However, caution must be taken when interpreting results due to the differences in scope, assay and instrument, and any thresholds applied in the final analysis. Further information about these comparisons is available from the Comparisons with other Australian surveys section of the Biomedical Results for Chronic Diseases, 2011-12 publication.

ENDNOTES

1 National Heart Foundation of Australia, 2013, Cholesterol, <http://www.heartfoundation.org.au/SiteCollectionDocuments/NAHU-Cholesterol.pdf>, Last accessed 08/07/2013.
2 National Heart Foundation of Australia and the Cardiac Society of Australia and New Zealand, 2005, Position Statement on Lipid Management - 2005, <http://www.heartfoundation.org.au/sitecollectiondocuments/the-lipid-position-statement.pdf>, Last accessed 22/10/2013.
3 Friedewald WT, Levy RI, Fredrickson DS,1972, Estimation of the low-density lipoprotein cholesterol in plasma without use of preparative ultracentrifuge, <http://www.clinchem.org/content/18/6/499.full.pdf>, Last accessed 22/10/2013.
4 Appleton CA, Caldwell G, McNeil A, Meerkin M, Sikaris K, Sullivan DR, Thomas DW, and DP Tognarini, Australian Pathology Lipid Interest Group, 2007, Recommendations for Lipid Testing and Reporting by Australian Pathology Laboratories, <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1904423/>, Last accessed 22/10/2013.