Recommendations for cholesterol testing come from the Adult Treatment Panel III guidelines, and are based on many large clinical studies, such as the Framingham Heart Study. For healthy adults with no cardiovascular risk factors, the ATP III guidelines recommend screening once every five years. A lipid profile may also be ordered at regular intervals to evaluate the success of lipid-lowering drugs such as statins. In the pediatric and adolescent population, lipid testing is not routinely performed. However, the American Academy of Pediatrics and the National Heart, Lung, and Blood Institute recommend that children aged 9–11 be screened once for severe cholesterol abnormalities. This screening can be valuable to detect genetic diseases such as familial hypercholesterolemia that can be lethal if not treated early. Traditionally, most laboratories have required patients to fast for 9–12 hours before screening. However, studies have questioned the utility of fasting before lipid panels, and some diagnostic labs routinely accept non-fasting samples. Typically the laboratory measures only three quantities: total cholesterol; HDL; Triglycerides. From these three data LDL may be calculated. According to Friedewald's equation:
LDL = Total cholesterol - HDL - Triglycerides/5
Other calculations of LDL from those same three data have been proposed which yield some significantly different results. VLDL may be defined as the total cholesterol that is neither HDL nor LDL. Then Friedewald's equation mentioned above yields:
VLDL = Triglycerides/5
The alternative calculations mentioned above may yield significantly different values for VLDL.
Implications
This test is used to identify dyslipidemia, many forms of which are recognized risk factors for cardiovascular disease and rarely pancreatitis. A total cholesterol reading can be used to assess an individual's risk for heart disease, however, it should not be relied upon as the only indicator. The individual components that make up total cholesterol reading—LDL, HDL, and VLDL—are also important in measuring risk. For instance, someone's total cholesterol may be high, but this may be due to very high HDL cholesterol levels,—which can actually help prevent heart disease. So, while a high total cholesterol level may help give an indication that there is a problem with cholesterol levels, the components that make up total cholesterol should also be measured.
