Medical history and physical examination. These points are an essential part of the diagnosis of hypercholesterolaemia and serve to rule out secondary causes.
Complete blood analysis (and urine, in some cases). This is the most important test to determine the cause. It can be used to rule out cases of hypercholesterolaemia due to other diseases such as diabetes, hypothyroidism or certain kidney or liver conditions. For a correct diagnosis, in addition to the total cholesterol, it is necessary to carry out a complete lipid profile including the amount of triglycerides and the levels of LDL (“bad”) and HDL (“good”) cholesterol. Very high total cholesterol, above 310 mg/dL in adults and 230 mg/dL in children, could be a sign of one of the serious genetic diseases that are also associated with early-onset cardiovascular disease (e.g., familial hypercholesterolaemia) and should therefore be studied in depth.
As a general rule, it is advisable for all people aged over 35–40 years (both men and women) to undergo a blood test to rule out hypercholesterolaemia. Individuals at particular risk, such as those with a family history of hypercholesterolaemia or heart attacks or strokes at a young age (under 55 years in men and 60–65 in women), or people with other cardiovascular risk factors such as diabetes, smoking or high blood pressure, should go for a screening test at an even younger age. A blood test is recommended for children whenever one of their parents has, or is suspected of having, a genetic form of hypercholesterolaemia.
Other, more complicated diagnostic tests, such as different blood tests or genetic studies, are only conducted in specific cases (when there is a suspicion of a genetic disorder, e.g., familial hypercholesterolaemia) and at specialised centres.
Does fasting influence the results of the blood test?
The condition a person should be in when they give a blood sample for a cholesterol test is cause for a certain degree of debate. In many cases a high cholesterol level is attributed to not having spent enough time fasting prior to the test. However, this is not strictly true. Cholesterol levels are very similar if measured when fasting or after a meal and therefore the results are perfectly valid for assessing whether or not an individual has high cholesterol, a risk of cardiovascular disease and if they need to begin treatment.
This is the conclusion of a European consensus paper written by specialists in the area, thus several scientific societies and agencies responsible for steering healthcare policies already recommend the tests are performed even without prior fasting.
Nevertheless, there are exceptions for individuals who must fast for other reasons such as to measure their blood sugar level or those with high triglyceride levels. In such cases recommendations are to do the test after fasting.