The laboratory assessment of lipid disorders

Abstract

The older 'traditional' lipid guidelines have placed undue emphasis on individually high-risk factors such as cholesterol. The aim of the TC cut-off points of 5.2 mmol/l and 6.2 mmol/l was to identify as many subjects as possible who have borderline to high risk and high risk for CHD respectively. This approach created the impression that all subjects with serum cholesterol greater than 5.2 or 6.2 mmol/l are at a higher or high risk for CHD and it ignored the fact that a cluster of coexisting, mildly abnormal risk factors may confer a much higher risk on an individual than only one very high risk factor. The latest guidelines suggest that these cut-off points should no longer be interpreted in isolation but rather against the background of the global CHD risk of a patient. This will avoid unnecessary treatment of patients who are not really at risk or alternatively identify patients who require aggressive lipid-lowering therapy even though their serum TC or LDLC may be only moderately elevated or may indeed be within the so-called desirable range. The repertoire of laboratory investigations to fully assess the patient's total risk for CHD needs to be done in a logical progression in order to answer the following 5 crucial clinical questions: Which patients should be targeted for lipid screening ? What variables can influence the validity of the results that need to be controlled ? What laboratory tests should be done on them ? What further laboratory tests are required in patients whose screening results justify possible intervention ? What laboratory tests are indicated in monitoring patients who receive lipidlowering drugs? The subsequent management of the dyslipidaemic patient will depend on the nature and severity of the disorder, i.e. predominant hypercholesterolaemia, predominant hypertriglyceridaemia or a combined disorder. More complex disorders such as type III (broad B band disease) and atypical presentations or clinical syndromes should be referred to specialist lipid clinics for further investigations. Lipid guidelines and risk assessment algorithms should be used to supplement, not replace clinical judgement.