In this article, we are going to see; What is a cholesterol test? How to use the lipid profile test to assess cardiovascular health? What, how & Why you need it?
What are lipids?
Lipids are fats and fat-like substances, and they are essential constituents of cells and energy sources.
Two essential lipids are cholesterol and triglycerides, which are carried in the blood by lipoprotein particles. Every lipoprotein particle contains a combination of cholesterol, triglyceride, protein, and phospholipid molecules.
What is a cholesterol test?
Other names for cholesterol tests are lipid profile test, lipid panel test, lipoprotein profile test, and lipoprotein panel test.
A lipid profile test is a useful screening test to diagnose abnormal high cholesterol. But you should combine it with advanced lipid testing for an accurate picture of total health.
A lipid panel measures lipoprotein particles that are classified based on their density; they are high-density lipoproteins (HDL), low-density lipoproteins (LDL), and very-low-density lipoproteins (VLDL).
A lipid profile test measures total cholesterol, LDL-C, HDL-C, and triglycerides. The test results are in mg/dL or mmol/L.
This test estimates total cholesterol, triglycerides, and HDL using ultra-centrifugation or chemical precipitation.
Why you need a cholesterol test?
Cholesterol produced by the liver is carried in the blood to deliver it to all the body cells.
High levels of cholesterol in the blood indicate the following:
- Inflammation in the body,
- Low thyroid function,
- Eating high carb diet (raised triglyceride levels),
- Weak digestion, leaky gut, allergy, ulcer, infection, etc.
- Liver problems,
- Kidney disease.
If your cholesterol levels are high, then you need to analyze your lifestyle for:
- high or improperly managed stress,
- inadequate or excess restless sleep,
- unhealthy diet, etc.
These are the things that promote inflammation that leads to high cholesterol. If these are not the cause of high cholesterol, then you need to undergo a set of test for the functions of thyroid, liver, and kidney.
To know how much cholesterol in the blood? You need to undergo a cholesterol test.
Details about the lipid profile test?
This cholesterol test provides information about
- Total cholesterol - It is the measure of the sum of all cholesterol by breaking down lipoprotein particles.
- Low-density lipoprotein cholesterol (LDL-C) - It is the calculated or measured cholesterol level in LDL particles. Mostly, the LDL-C is calculating from the results of total cholesterol, HDL-C, and triglycerides.
- High-density lipoprotein (HDL) - It is the measure of the cholesterol in HDL particles. HDL-C carries excess cholesterol and delivers it to the liver for removal.
- Triglycerides (the most common form of fat in the blood) - It measures the triglycerides in all the lipoprotein particles. Most of the triglycerides are in the very low-density lipoproteins (VLDL).
Other information reported in the lipid panel is parameters calculated from the results of the tests listed above.
Total cholesterol is the sum of cholesterol in all the lipoprotein particles (VLDL, LDL, and HDL).
TC = LDL-C + HDL-C + VLDL-C
High-density lipoprotein cholesterol (HDL-C)
Labs measures HDL cholesterol by separating HDL lipoproteins from other lipoprotein fractions and measure the cholesterol in the HDL particles.
Low-density lipoprotein cholesterol (LDL-C)
Most labs use Friedewald formula to calculate LDL cholesterol.
Most labs estimate the concentration of low-density lipoprotein cholesterol using Friedewald formula as below:
LDL-C = TC – HDL-C - TG/5
This formula is based on the typical composition of VLDL. This formula is useful only if the triglyceride is within 100 to 400 mg/dl or 1.129 to 4.516 mmol/l. Otherwise, it will give the wrong LDL-C number.
A clinical study published in the Journal of the American College of Cardiology found this method for calculating LDL-C levels may often produce inaccurate results.
This indirect LDL-cholesterol estimation is unreliable when the triglyceride levels are low. Ref: The Impact of Low Serum Triglyceride on LDL-Cholesterol Estimation, published in Arch Iranian Med 2008; 11 (3): 318 – 321.
If your triglyceride is below 100 mg/dl or 1.129 mmol/l, then you can use this formula:
LDL-C (mg/dL) = TC/1.19 + TG/1.9 – HDL/1.1 – 38
LDL-C (mmol/L) = TC/1.19 + TG/0.81 – HDL/1.1 – 0.98.
Very low-density lipoprotein cholesterol (VLDL-C)
Calculation of VLDL-C is from triglycerides divided by 5; this formula is based on the typical composition of VLDL particles.
VLDL-C – TG/5
Non-High-density lipoprotein (non-HDL-C)
Some labs provide non-HDL cholesterol calculated from total cholesterol minus HDL-C.
Non HDL-C = TC – HDL-C
A flaw in the cholesterol test!
There is a problem with the cholesterol test; it measures just cholesterol in the lipoprotein. This test does not provide the size or number of particles.
Various studies confirm that small LDLs and large HDLs have a cardiovascular risk. Additionally, high LDL particle and low HDL particle numbers are risks towards heart disease.
But lipoprotein particle number and size measurement tests are costlier compared with the traditional test. Additionally, it is not available everywhere. So, alternatively, we can utilize the lipid profile test to assess the particle number and size.
How to use the lipid profile test to assess cardiovascular health?
LDL-C has a link with heart disease risk; however, there are 2 LDL variants; they are large buoyant and small dense.
LDL has closely associated with heart disease. But there are two LDL variants; one is large, buoyant not associate with heart disease, and another small, dense associated with heart disease.
If there is no access to LDL-P measurement, the next best markers are triglycerides and HDL.
High levels of triglyceride indicate the presence of small LDL-P, insulin resistance, and metabolic syndrome.
Certain HDL and triglyceride level indicate the presence of dangerous LDL-B particles; they are:
- High triglyceride levels, i.e. over 120 mg/dL or 1.35 mmol/l;
- HDL levels of below normal, i.e. 40 mg/dL or 1.03 mmol/l in men and 50 mg/dL or 1.29 mmol/l in women;
A low level of triglycerides indicates the presence of harmless LDL-A particles.
Usually, the elevated triglyceride is the result of high VLDL. Lowering triglyceride levels can proportionally convert from small, dense LDL into large, fluffy molecules.
Triglyceride to HDL-C (TG/HDL) ratio
The study shows triglyceride/HDL cholesterol ratio of over 3.8 increases the chance for phenotype B.
The triglyceride/HDL-C ratio is a better prediction of the LDL phenotype B. Ref: American Journal of Cardiology Volume 94, Issue 2, pages 219-222, 15 July 2004.
The triglyceride/HDL-C ratio is useless for African-Americans. They do not have high triglycerides, even with severe insulin resistance. Because they own a different lipase type enzyme to metabolize triglyceride expression, their insulin resistance should assess by glucose abnormalities, obesity, and hypertension. It is not by high triglycerides and or low HDL cholesterol.
LDL-P assessment from lipid profile test
Patient with triglyceride over 130 mg/dl or 1.47 mmol/l indicates high ApoB particles (LDL) count.
TG/HDL-C ratio is just predicting the LDL size (not particle concentration LDL-P). But, most patients with small LDLs have increased numbers of LDLs. Ref: Diabetes Care 2005; 28; 1798-1800.
Non-HDL-C is a better marker of cardiovascular risk than LDL-C. Non-HDL-C is a better way to correlate with the LDL particle number. Also, it is immediately available from the lipid profile test.
Total cholesterol minus HDL-C gives non-HDL-C; i.e., Non-HDL-C = TC - HDL-C.
Non–HDL-C and ApoB are the best predictors of CHD than the cholesterol it carries. Reference: Circulation 2005; 112: 3375-3383.
How to prepare for the Cholesterol Test?
To undergo a complete lipid profile, you need to avoid eating or drinking anything except water and medications for a minimum of nine hours, ideally twelve hours, and a maximum of fifteen hours before a cholesterol test.
However, if you are taking only HDL and total cholesterol levels, then you may not require fasting.
How is the cholesterol test performed?
Your doctor requires to get a blood sample from you in the morning after fasting. It is an outpatient procedure performed at a diagnostic lab; it takes a few minutes with relatively no pain.
What does the test result mean to you?
If your cholesterol numbers are in an abnormal range, then you may be at a higher risk of heart disease, stroke, and atherosclerosis. If your cholesterol test results are higher than usual, then your doctor may order a thyroid function test to know whether your thyroid is underactive.
Can cholesterol tests give the wrong result?
Clinical factors that may cause lipid test error result include but are not limited to the following:
- Illness such as severe infection or myocardial infarction (uhn·faark·shn),
- Improper fasting,
- Interference from the medication such as oral contraceptives or corticosteroids,
- Human (test) error,
- Pregnancy or phase of the menstrual cycle.
Also, other factors such as alcohol, smoking, posture, exercise, and prolonged tourniquet (tur·nuh·kuht) use may produce an error in the result of false positive or negative.