LDL cholesterol, commonly known as "bad" cholesterol, is a molecule from the group of lipoproteins that actively participates in the transport of cholesterol throughout the body. LDL cholesterol is not known for its involvement in the atherosclerotic process, which is the cause of heart attacks and other cardiovascular diseases. Who should get an LDL cholesterol test? How to lower its too high level?

LDL cholesterol(Englishlow density lipoprotein ), commonly referred to as bad cholesterol, belongs to the group of low-density lipoproteins. The LDL molecule consists of esterified and free cholesterol, phospholipids and triglycerides.

In addition, so that LDL particles can freely mix with the blood (cholesterol and triglycerides are insoluble in water), LDL cholesterol also includes proteins. The main protein in the LDL molecule is apolipoprotein-B.

LDL cholesterol - functions in the body

LDL cholesterol is formed in the blood by the removal of triglycerides from other lipoproteins called VLDL by lipoprotein lipase. The main function of LDL cholesterol istransporting free cholesterolin the body to places where it is needed for the repair of damaged cells or the synthesis of bioactive substances such as hormones.

The receptor for LDL cholesterol is found in the liver and other organs, such as the muscles. The receptor, connecting to, inter alia, with apolipoprotein-B, causes the entry of LDL cholesterol into the cell. It then breaks down to release free cholesterol.

Excess LDL cholesterol is stored inliver , but it can also accumulate inthe blood vessel wall . Once deposited in the vessels, LDL cholesterol is very susceptible tooxidation in the presence of free radicals. This happens when the body has chronic inflammation caused by e.g. obesity or diabetes.

The resulting oxidized LDL particles (abbreviated as oxLDL) stimulate the formation of atherosclerotic plaque, which over timestiffens and constricts the blood vessels . And this, in turn, is the cause of a heart attack and stroke.

LDL cholesterol - what is the test?

LDL cholesterol testing is performed withvenous bloodtaken from the elbow bend. Habits should not be radically changed a few days before the testnutritional.

LDL cholesterol is most often calculated indirectly fromFriedewald formulabased on the results of other tests:

  • total cholesterol
  • HDL cholesterol
  • triglycerides.

This is the so-calledcalculated LDLand must necessarily be doneon an empty stomach , approximately 12 hours after the last meal. Additionally, this method should not be used when the triglyceride concentration is above 400 mg / dL.

In some laboratories, LDL cholesterol can be measured directly and it is calleddirect LDL . This test does not need to be performed on an empty stomach.

LDL cholesterol - when to test?

The LDL cholesterol test is ordered as part of a lipid profile that includes tests for triglycerides, total cholesterol, and HDL cholesterol in addition to LDL cholesterol. The LDL cholesterol test is the most important parameter of the lipid profile predicting the risk of cardiovascular disease. In addition, it is used as the main target of lipid disorders therapy.

LDL cholesterol testing should be ordered from:

  • men over 40
  • women over 50
  • people on an incorrect diet
  • smokers
  • chronically stressed people
  • alcohol abusers
  • physically inactive people
  • people with hypertension
  • overweight and obese people
  • people with metabolic syndrome
  • people with thyroid diseases
  • people with kidney problems
  • people with inflammatory diseases, e.g. rheumatoid arthritis, diabetes
  • people with a genetic predisposition to high cholesterol

Adults who test normal for LDL cholesterol should be repeated no later than3-5 years . In adults with abnormal test results, after treatment and normalization of LDL levels, testing should be repeatedannually .

However, in children with a family history, e.g. family hypercholesterolaemia, the examination of LDL cholesterol and other parameters of the lipidogram should be screened at the age of9-11 years . If the test results are correct, it should be repeated around the age of 18.

LDL cholesterol - the norm in adults

  • in people from a very high-risk group, incl. with known cardiovascular disease, complicated diabetes, severe chronic kidney disease, LDL cholesterol values ​​should bebelow 70 mg / dL
  • in high-risk people, incl. with familydyslipidemia, severe hypertension, uncomplicated diabetes, moderate chronic kidney disease, LDL cholesterol values ​​should bebelow 100 mg / dL
  • other people's LDL cholesterol values ​​should bebelow 115 mg / dl

LDL cholesterol - how to interpret the test result?

Too high LDL cholesterol increases the risk of cardiovascular diseases such as heart attacks and strokes. The causes of too high LDL cholesterol are:

  • genetic diseases, e.g. family hyperlipidemia
  • high triglyceride concentration
  • obesity
  • metabolic syndrome
  • diabetes
  • hormonal disorders
  • drugs, e.g. steroids
  • liver and intestine diseases
  • smoking
  • alcohol abuse

LDL cholesterol levels increase in pregnant women, so it should be measured at least6 weeks after childbirth.

Lowered LDL cholesterol is observed during acute illness, immediately after a heart attack and after trauma, for example after surgery. Therefore, the determination of LDL cholesterol should be performed at least6 weeks after the end of the disease .

LDL cholesterol - how to lower its level?

Apart from medications, the greatest impact on reducing LDL cholesterol is the change in lifestyle, including diet. Too high LDL cholesterol can be lowered by restricting consumption:

  • saturated fatty acids contained in animal products such as: dairy, meat, lard;
  • trans fats contained incl. in ready-made confectionery and fast food.

It has been estimated that converting 1% of energy from saturated fat to energy from monounsaturated fat (e.g. olive oil) reduces LDL cholesterol by 1.6 mg / dL. Conversely, the conversion of energy into polyunsaturated fatty acids (e.g. from fish oils) causes a decrease by 2 mg / dl.

The LDL cholesterol level is also positively influenced by the inclusion of functional foods containing plant phytosterols in the diet and the consumption of dietary fiber, which limits the absorption of fats in the intestine.

In addition, it is worth noting that losing excess kilograms and physical activity reduce LDL cholesterol. It is estimated that for every 10 kg lost, LDL-C cholesterol is reduced by 8 mg / dL.

LDL cholesterol - familial hypercholesterolaemia

The regulation of LDL cholesterol in the blood is done onthe level of the LDL cholesterol receptor in the liver. When the number of receptors on the surface of the liver cells decreases, the liver's ability to take up LDL cholesterol is lowered, which leads to an increase in it in the blood. Conversely, when the number of receptors increases, the liver takes in more LDL cholesterol, which lowers it in the blood.

Malfunctioning of the LDL cholesterol receptor is the cause offamilial hypercholesterolaemia , an inherited disease caused by mutations in the LDLR gene. The disease is characterized byhigh levels of triglycerides and LDL cholesterol in the blood .

Mutations cause a decrease in the number of LDL receptors, a decreased ability of the liver to take up LDL cholesterol, and an increase in its level in the blood. If a person has only one defective copy of the LDLR gene, the increase in LDL cholesterol is approximately300 mg / dL . However, in the presence of two defective copies of the gene, levels can be as high as1000 mg / dL .

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About the authorKarolina Karabin, MD, PhD, molecular biologist, laboratory diagnostician, Cambridge Diagnostics Polska A biologist by profession, specializing in microbiology, and a laboratory diagnostician with over 10 years of experience in laboratory work. A graduate of the College of Molecular Medicine and a member of the Polish Society of Human Genetics. Head of research grants at the Laboratory of Molecular Diagnostics at the Department of Hematology, Oncology and Internal Diseases of the Medical University of Warsaw. She defended the title of doctor of medical sciences in the field of medical biology at the 1st Faculty of Medicine of the Medical University of Warsaw. Author of many scientific and popular science works in the field of laboratory diagnostics, molecular biology and nutrition. On a daily basis, as a specialist in the field of laboratory diagnostics, he runs the content department at Cambridge Diagnostics Polska and cooperates with a team of nutritionists at the CD Dietary Clinic. He shares his practical knowledge on diagnostics and diet therapy of diseases with specialists at conferences, training sessions, and in magazines and websites. She is particularly interested in the influence of modern lifestyle on molecular processes in the body.

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