Cholesterol is a type of body fat, or lipid. A person’s serum cholesterol level represents the amount of total cholesterol in their blood.

A person’s serum cholesterol level comprises the amount of high-density lipoprotein (HDL), low-density lipoprotein (LDL), and triglycerides in the blood. Triglycerides are a type of fat bundled with cholesterol.

A person’s serum cholesterol level can indicate their risk of developing conditions such as heart disease.

In this article, we explore what serum cholesterol shows, what optimal ranges are, and how to improve levels with changes to lifestyle and diet.

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Cholesterol is a waxy, fatty substance. Cells in the liver produce it and release it into the bloodstream.

With a blood test, a doctor can measure levels of:

  • HDL cholesterol
  • LDL cholesterol
  • triglycerides

A doctor will calculate total serum cholesterol by summing the HDL level, the LDL level, and 20% of the triglyceride level present in a blood sample.

Learn more about cholesterol levels here.

Cholesterol plays a vital role in many bodily processes, including:

  • building cellular membranes
  • making hormones
  • metabolizing vitamin D in the skin
  • producing bile acids to digest fatty foods

People often refer to LDL cholesterol as “bad” cholesterol and to HDL cholesterol as “good” cholesterol.

LDL cholesterol can build up in a person’s arteries, clogging them and reducing blood flow. This is why cholesterol has links to heart disease.

While LDL cholesterol builds up and blocks arteries, HDL cholesterol attaches to other cholesterol in the blood and unsticks it from artery walls.

Doctors previously determined whether a person’s serum cholesterol level was healthy by comparing it against established optimal ranges.

Previously used guidelines, expressed in milligrams per deciliter (mg/dl) of blood, are as follows:

Age and sexTotal serum cholesterolHDL levelLDL levelTriglycerides
all aged 19 years and younger170 mg/dl at mostat least 45 mg/dlless than 100 mg/dlless than 150 mg/dl
females aged 20 years and older125–200 mg/dlat least 50 mg/dlless than 100 mg/dlless than 150 mg/dl
males aged 20 years and older125–200 mg/dlat least 40 mg/dlless than 100 mg/dlless than 150 mg/dl

Currently, however, doctors typically take a wider range of factors into account when deciding whether an individual’s cholesterol levels require corrective treatment.

Some risk factors a doctor may consider when evaluating a person’s serum cholesterol level include:

Typically, a person with higher levels of HDL cholesterol and lower levels of LDL cholesterol will have a more optimal serum cholesterol measurement.

This is because HDL cholesterol helps reduce the presence of LDL cholesterol in the blood. It can also prevent LDL cholesterol from collecting and from forming hard deposits, or plaques, which stick to artery walls and reduce blood flow.

Plaques can become so large that they cause the arteries to narrow and stiffen over time. This in turn can lead to ischemic heart disease and cerebrovascular disease, such as stroke and vascular dementia.

A significant amount of LDL cholesterol in arteries can prevent enough blood and oxygen from reaching organs and tissues, resulting in severe health complications.

A cholesterol plaque buildup can break off and move to different arteries in the body. This will make the blockage of blood more severe, as it can lead to a stroke.

Cholesterol embolism, which is a clot that moves, can also occur in different parts of the body, including other organs, such as the kidneys, and cause damage.

Complications of high serum cholesterol levels include:

How triglycerides impact health is less clear. However, high levels of triglycerides may be a risk marker of other conditions, such as heart disease.

Moreover, extremely high triglyceride levels can cause pancreatitis.

The liver produces enough cholesterol to meet all of the body’s needs. Any cholesterol a person consumes through food and drink is excess.

Changing the diet is an effective way to lower LDL cholesterol levels. Reducing the consumption of trans fats can be an important first step in bringing cholesterol levels down.

According to the American Heart Association (AHA), trans and saturated fats should account for no more than 6% of a person’s daily intake of calories.

If a person consumes 2,000 calories per day, they should only take in 11–13 grams of saturated fats per day.

Other dietary and lifestyle changes that can help people reach optimum cholesterol levels include:

  • eating fewer full fat dairy products, such as whole milk, butter, cream, and cheeses
  • eating less red meat, pork, lamb, and poultry with skin
  • avoiding heavily processed foods
  • limiting the consumption of oils high in trans fats
  • eating fewer refined carbohydrates, such as those present in pastries, breads, crackers, and chips
  • avoiding sugary foods and drinks, such as candy, chocolate bars, juices, pre-made smoothies, sodas, and energy drinks
  • quitting smoking, if applicable
  • reducing alcohol consumption, if applicable
  • exercising regularly
  • addressing related medical conditions, including diabetes and high blood pressure

Keeping a food diary can help a person identify room for improvement and develop healthier habits.

The following activities can boost a person’s levels of HDL cholesterol:

  • using oils with fewer trans fats, such as those from olives, sunflowers, canola, and corn
  • eating more whole fruits and vegetables
  • eating more whole grains and cereals
  • replacing meat with plant-based protein sources, such as tofu and quinoa
  • eating skin-free poultry and fish such as salmon, trout, herring, and mackerel
  • increasing their intake of dietary fiber
  • drinking low fat milk or replacing milk with a dairy-free alternative
  • getting regular exercise

A doctor may prescribe medications for people with high cholesterol for whom dietary and lifestyle changes prove ineffective.

Serum cholesterol can give an overview of a person’s cholesterol levels. The number of triglycerides and LDL and HDL cholesterol in the blood can indicate the risk of a severe heart condition, such as a heart attack or stroke.

The AHA recommends that adults older than 20 have their serum cholesterol levels and other indicators of heart disease checked every 4–6 years.

A person with a higher risk of complications related to high blood pressure may need to have their serum cholesterol levels checked more frequently.

Individuals with diabetes should also test their cholesterol levels more often, as diabetes can increase the levels of LDL cholesterol. It is also a risk factor for heart disease.