fasting cholesterol levels

[angela9249]

does anyone know how much difference fasting makes on cholesterol and trigylercide levels? My Dr. has been treating me for high on both but I never fasted before my test.

[gymdandee]

Some cholesterol tests require you to fast, while others are not affected by food intake.

A total cholesterol test involves one measurement, which combines LDL, or bad, cholesterol and HDL, or good, cholesterol. It is not necessary to fast before a total cholesterol test because the value does not change significantly after eating, according to the Harvard Health Publications. A lipid profile, which includes values for total cholesterol, as well as individual values for LDL cholesterol, HDL cholesterol and triglycerides, another lipid in the blood, requires you to fast.

LDL levels cannot be measured from the blood directly. Instead, a mathematical equation called the Friedewald equation, is used to calculate LDL levels using values for total cholesterol, HDL cholesterol and triglycerides. The equation divides your triglyceride level by 5 and then subtracts this value as well as your HDL value from your total cholesterol. The result is your LDL level. When you eat, your triglyceride levels rise 20 to 30 percent, according to the Harvard Health Publications. Because this increase in triglycerides affects the outcome of the Friedewald equation significantly, it is necessary to fast before a lipid profile, individual LDL test or triglyceride screening.

According to the Health Services at Columbia, fat and cholesterol components are usually only measurable for approximately 10 hours after a meal. Because of this, most physicians recommend fasting for a period of at least 12 hours before a fasting cholesterol test. Alcohol can increase your triglyceride levels significantly, so abstain from alcohol for at least 24 hours before a fasting cholesterol test.

[Flycaster305]

A quick answer would be that doctors expect you to fast at least twelve hours but fourteen hours is preferable.   My Cardiologist suggests I continue my usual diet until fourteen hours prior to a cholesterol/trig test as he wants to see how my normal, usual lifestyle is affecting my cholesterol/trig level.  
If you aren't fasting, you aren't getting an accurate level unless you are being tested for specific issues.

[erijon]

Welcome and thanks for your question. I should start by stating that my opinion is that fasting is necessary prior to lipid testing in order to get an accurate base line of your levels. Having said that, there is mounting evidence that fasting is not as important as once thought based on a study of 300,000 individuals, whether or not they fasted and their eventual outcome. Below is a link that is very interesting reading on the subject;

http://cholesterol.about.com/b/2009/11/11/cholesterol-testing-to-fast-or-not-to-fast.htm

I had an interesting discussion about this with my doctor this past week as I got the results of my lipid and basic metabolic screening. In my case, I had two numbers that were high in my metabolic panel, my creatinine and BUN levels. I asked my doctor about these and he said they were fine even though they were elevated. When I pressed for further explanation, he told me that the only way to get an accurate reading was to not consume any protein for 24 hours before the test. Obviously I asked why bother with it and he responded that as doctors they are watching the trend, not necessarily the number. As long as your numbers are consistent from year to year, then there is no issue. I found that a little unnerving to be frank.

In any case, the final outcome of the study in the above listed link was the main focus of lipid testing should still be on HDL and LDL levels as they are the best marker for the development of CAD. I still question the notion that fasting is no longer thought to be as important as before.

Just another perspective, hope this helps.

Jon

[Occupant]

"LDL levels cannot be measured from the blood directly. Instead, a mathematical equation called the Friedewald equation, is used to calculate LDL levels using values for total cholesterol, HDL cholesterol and triglycerides."
I've seen that equation before, but when I got my latest results back, it said "LDL (DIRECT MEASURMENT)". I had never seen that before, but when you brought it up, I looked at it again. Since my Total Cholesterol and HDL don't carry the same notation, I assume those are the values calculated.

[angela9249]

Thank you all for your response. that answered my question!

[gymdandee]

Direct measurements of LDL are determined without a calculation. Although not as commonly performed, direct LDL measurements can be used in cases where triglycerides are very high. In some cases, these test kits can measure other lipid particles in addition to LDL, such as LDL subtypes and apolipoproteins. However, not everyone needs a more extensive lipid profile tested. Additionally, these tests are usually more expensive than using the Friedewald equation to calculate LDL. Because of this, they are not as widely used.