Cholesterol, LDL
fS-Kol-LDL KL 2099
Part study of the Lipid profile test package
Approximately 65-70% of the cholesterol present in the bloodstream is carried by LDL particles. Cholesterol initially stored in the liver is transported into the bloodstream through VLDL particles, which are produced by the liver. While in the bloodstream, VLDL particles transform into IDL particles (VLDL remnants), eventually becoming LDL particles, with some VLDL remnant particles leaving the liver.
The cholesterol esters within the LDL particle are transported to target cells through the LDL receptor. These cholesterol esters can be hydrolyzed into free cholesterol, serving as building material for cell membranes or as a precursor for steroid hormones. When the LDL particle fails to encounter the LDL receptor in tissues, it returns to the bloodstream via the lymphatic fluid. However, a significant portion of LDL particles are transferred to the liver via LDL receptors, where cholesterol esters are released and become part of the liver’s cholesterol metabolism.
LDL-cholesterol measurement is an essential part of diagnostic tests for dyslipidemia, which involves abnormal fat values in the blood. Other tests include fS-Chol, fS-HDL-C, and fS-Trigly. To accurately diagnose dyslipidemia, at least two samples must be taken on different days, and the levels of total cholesterol, HDL cholesterol, LDL cholesterol, and triglycerides are determined.
Indications
Monitoring the treatment of hypercholesterolemia. Assessment of risk for coronary artery disease.
Sample
1 mL of fasting serum, minimum 0.5 mL.
Storage and delivery
The sample can be refrigerated for up to a week, but for longer storage, it should be kept frozen. Delivery at room temperature, if it arrives within 24 hours.
Method
Photometric, enzymatic. Accredited method.
Turnaround time
1 – 2 weekdays
Reference values
Recommended value below 3.0 mmol/L.
The target value is determined according to the Dyslipidemiat Käypä hoito (Current Care Guidelines for Dyslipidemias) recommendation published on October 27, 2020, by the Finnish Medical Society Duodecim and the Finnish Association of Internal Medicine.
Addition to the target values of LDL-Cholesterol:
Target values on the total risk assessment of arterial disease:
| Below 2.6 mmol/L | Moderate risk |
| Below 1.8 mmol/L | High risk |
| Below 1.4 mmol/L (or as close to it as possible) | A particularly high risk |
Interpretation of results
A high serum cholesterol concentration is a significant risk factor in the development of atherosclerosis. The most common cause of increased cholesterol levels is elevated LDL cholesterol, which can result from both hereditary and environmental factors.
Familial hypercholesterolemia (FH disease), attributed to hereditary factors, can lead to elevated cholesterol levels. It arises due to a mutation in the gene encoding the LDL receptor, hindering the transfer of LDL cholesterol to the liver and resulting in an increased serum LDL cholesterol value. The prevalence of the heterozygous form in Finland is estimated to be around 1 in 600 individuals, with LDL cholesterol concentration being 2-3 times higher than the rest of the population. The most common gene mutations observed in Finland are FH-North Carelia and FH-Helsinki.
Another common inherited form of dyslipidemia is Familial Combined Hyperlipidemia (FCH), affecting 1-2% of the population. FCH involves several gene mutations that predispose individuals to the disease, and environmental factors like age and overweight also influence its manifestations. One potential cause of the lipid metabolism disorder is thought to be the overproduction of apoprotein B, associated with LDL cholesterol, or a dysfunction of lipoprotein lipase, which may lead to the accumulation of particularly harmful small and dense LDL particles in the bloodstream. This is reflected in an increased serum apoB concentration rather than an elevated LDL-cholesterol concentration.
More commonly, hypercholesterolemia is linked to the so-called common polygenic hypercholesterolemia, which involves multiple genetic variants and environmental influences. Dietary habits play a significant role in this group. In the Finnish population, the hereditary factor apoprotein type E4 is more prevalent than usual, occurring in about a third of Finns. Individuals with type E4 are considered to have a special sensitivity to dietary cholesterol. Obesity and a low dietary fiber intake can also contribute to increased LDL cholesterol concentration.
Elevated LDL cholesterol levels may also occur in conditions such as hypothyroidism, kidney failure, nephrotic syndrome, diabetes, biliary obstruction, and during pregnancy.
On the other hand, low LDL cholesterol values are found in hyperthyroidism, malnutrition, malabsorption, among vegetarians, individuals with chronic diseases, and those using statin medication.
Literature:
Dyslipidemiat, Käypä hoito-suositus, 14.12.2022. Suomalaisen Lääkäriseuran Duodecimin ja Suomen Sisätautilääkärien Yhdistys ry:n asettama työryhmä
Ravitsemustiede, Duodecim 2021 (toim. M. Mutanen, H. Niinikoski, U. Schwab, M. Uusitupa)
Inquiries
martin.tornudd@milalab.fi
Last update 8.8.2023
