Heart Disease: How is it Diagnosed?

There are many different methods used to diagnose heart disease from lab values, to an electrocardiogram, stress test, CT heart scan, or MRI of the heart.  If you are over 40 or have a family history of heart disease, it is important to discuss your risk for heart disease with your doctor. 

Your doctor will likely discuss key lifestyle areas that could represent risk for heart disease including diet, exercise, smoking, and stress.  A fasting blood lipid panel will also be ordered to measure the total cholesterol, low-density lipoproteins (LDL), high-density lipoproteins (HDL), and triglycerides in your blood.  Abnormalities in these values can represent a risk for heart disease.

Understanding Your Lab Values

Most people understand that a total cholesterol level under 200 mg/dl is desirable, and levels significantly over this represent increased risk for heart disease.  But how do LDL, HDL and triglycerides fit into the picture?

LDL and HDL are both complex particles called lipoproteins.  Lipoproteins transport lipids, including cholesterol, in the blood.  LDL and HDL differ in the ratio of protein to lipids and are classified based on their density.

LDL = low density lipoprotein; is highest in cholesterol esters as a % of weight

HDL = high density lipoprotein; is highest in density due to a high protein/lipid ratio

LDL transports lipids through the blood stream to various tissues throughout the body.  The LDL attaches to a cell membrane via an LDL receptor to deliver cholesterol for cell membrane synthesis.  The cell membrane requires cholesterol for normal structure and function.  However, excess cholesterol not needed by cells remains in the blood as LDL which can play a role in the development of atherosclerotic plaque in blood vessels.  Thus, high blood levels of LDL correlate with higher risk of heart disease.

HDL has an entirely different and more beneficial role in the body.  HDL functions to transport cholesterol from tissues and from other lipoproteins to the liver.  The liver can then excrete excess cholesterol as bile acids necessary for digestion of dietary fats.  Thus, high blood levels of HDL correlate with lower risk of heart disease.

A triglyceride is a glycerol molecule with three attached fatty acid chains.  Triglycerides are derived from fats in foods, but may also be metabolized from carbohydrates and sugars by your liver.  They are the storage form of fat in your body, a concentrated source of energy available when your body needs it.  If you eat more food than your body needs for energy and repair, it will be converted to triglycerides and stored for future use.  Your triglyceride level can vary greatly depending on the content and size of your meals so it is important to fast for 8-12 hours prior to your blood draw.

The classification of each of the blood lipids is shown in the table below.

Classification of LDL, Total, and HDL Cholesterol (mg/dL)

Lab Value	Classification
Total Cholesterol
<200	Desirable
200-239	Borderline high
≥240	High
LDL Cholesterol
<100	Optimal
100-129	Near optimal/above optimal
130-159	Borderline high
160-189	High
≥190	Very high
HDL Cholesterol
<40	Low
≥60	High
Triglycerides
<150	Normal
150-199	Borderline high
200-499	High
≥500	Very high
Cholesterol Ratios
Total Cholesterol:HDL	Optimal is 3.5:1 (goal <5:1)
LDL:HDL	Optimal is <3:1

Source:  Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). National Institutes of Health, National Heart, Lung, and Blood Institute.

The results of your blood lipid panel are a good starting point to understand how your diet and lifestyle are affecting your heart health.  Some cardiologists have begun to also use lipoprotein particle concentration and size measures to evaluate risk of heart disease.  Tests are also used to test for genetic components that may contribute to abnormal lipid profiles.

Unless your doctor identifies a genetic component to your abnormal lipid levels, diet and lifestyle play a major role in improving your cholesterol and triglyceride levels.  After we set the foundation with a good understanding of what heart disease is and how it is diagnosed, I will include current information about foods that will help you reduce your cholesterol and your risk of heart disease.

In the next post, I will cover the diagnosis of high blood pressure, and the connection between elevated blood pressure and the development of atherosclerosis.