should I be worried about my cholesterol?
May 13, 2011 1:37 PM   Subscribe

How much does eating vs fasting prior to the blood test affect your cholesterol reading?

My doctor insisted on me getting a blood test when I came in for something totally unrelated, because I've never had one before. I didn't fast that day, I had breakfast (smoked salmon! doesn't that have cholesterol?) and a snack by 2pm, when my blood was drawn. I should have resisted and said I will come in another morning after fasting several hours, but I had other stuff on my mind then.

My total cholesterol came back as 198 (they said they didn't do separate HDL/LDL analysis because I didn't fast and it wouldn't be accurate anyway). 198 is high, but how much of that is because I didn't fast?

Does anyone know approximately how much higher the cholesterol reading is after eating, vs getting blood drawn after fasting overnight? For example, if it only increases ~10 mg/dL after eating, then I should still be concerned about being in the higher range of normal. If it nearly doubles after eating, then I am probably OK (although I know HDL/LDL ratio is still important to determine what is healthy).

[Yes, I will get another test done in a couple of months, properly this time. And yes, I can ask my doctor, but I am not too crazy about her, which is why I am asking internet strangers for a ballpark figure, and I will probably be switching doctors.]
posted by to Health & Fitness (10 answers total) 1 user marked this as a favorite
198 is really only high if it's the result of summing a low HDL with a high LDL. I mean, it makes sense to always try to do things in a manner to optimize your health, but I wouldn't give this test a second thought.
posted by telegraph at 1:43 PM on May 13, 2011

200 is kind of an arbitrary number. At 198 you cholesterol is ok, at 201 it's high. If you know you lead an unhealthy lifestyle, you should be changing it no matter what your total cholesterol is. And if you lead a healthy lifestyle than a high side of normal reading is mostly genetic, and you probably aren't going to be able to do much about it anyway.

I'm not aware of any data that suggests a high side of normal reading, absent any other significant risk factors, puts you at an increased risk of stroke or heart attack.
posted by COD at 1:56 PM on May 13, 2011

It's not that salmon has cholesterol-- it's that it has fat. That affects your cholesterol levels.

If you ate breakfast at 7, and your snack was just a cup of black coffee, and they drew the cholesterol at 2-- then I'd expect the draw to be about accurate. I think they say 12 hours fasting for most outpatient stuff like this, but 7 ought to be enough. If that snack was anything earlier than a minute pre-draw, and consisted of any actual food-- well, it's a mystery! These things aren't calibrated to people with food in them; what it's measuring is how your specific body handles cholesterol, after all, so there are no guidelines about x food -> y cholesterol.

198 isn't worth worrying about unless there are other problems. Aren't recommendations still for <2>200 cholesterol, depending on the specific person's demographics (sounds like you're a woman from profile-- treating women without cardiovascular disease is one of the contentious issues).

Frankly, I'm surprised they even did the blood draw. But yeah, it's not a big deal, don't worry. If you want to worry about something, quit smoking, or increase your level of activity.
posted by nathan v at 2:06 PM on May 13, 2011 [1 favorite]

I am not a doctor, but I wouldn't put much stock by that number alone. My fasting cholesterol is 196 or 197, but my doctor doesn't seem too concerned since my ratio is OK and my LDL is in the middle of the normal range.

I can't visit this link at work, but it's quoted here
Scientists at the National Heart, Lung, and Blood Institute have concluded that LDL will be underestimated by approximately two to four percent and HDL levels underestimated by about one to four percent. In addition, triglyceride (TG) levels, another component of the cholesterol test, will be overestimated by roughly 20 mg/dL. Though small, these numbers might seem more meaningful if your measurements are borderline high.
posted by muddgirl at 2:14 PM on May 13, 2011

Short explanation: IIRC, a 20-30% increase in triglycerides after eating or drinking alcohol, and most of the time, they determine LDL from the the triglyceride level mathematically.

Longer explanation based on my pharm class slides:
There's a bunch of types of cholesterol with different densities: High density (HDL) is 'happy' or 'good' cholesterol, and low density (LDL) is 'loser' or 'bad' cholesterol. Triglycerides (TG) are a very low density lipoprotein (VLDL) and are also losers.

Most medical cholesterol therapy is made on the basis of lifestyle, family and personal history, and LDL levels, since the drugs mostly work by lowering LDL levels (although not all, and most of them raise HDL also.)

The tests work by measuring total cholesterol, HDL, and TG. Total cholesterol is a sum of HDL, TG, and LDL. But they indirectly measure LDL from TGs - I think I saw somewhere that it's about 85% specific, but in most people that's fine. TGs are in part made up of different kinds of even more detailed particles, one of which in particular go up after a meal/drinking. Therefore, if one doesn't think one has an accurate TG from a person, one can't calculate an accurate LDL. If you can't have *that* be specifically accurate, you can't math out any of it and the total's all that really is accurate.

That being said, current guidelines say less than 200 total is fine, unless there's a particular reason to think your ratio is off - the 'risk factors' on my slides that aren't lab values are cigarette smoking, hypertension, diabetes, family history of early coronary disease, age above 45/55 m/f.
posted by cobaltnine at 2:14 PM on May 13, 2011

Best answer: IANAD, but I would never base a diagnosis or anything important on a cholesterol test that hadn't been done while I'd been fasting 8-12 hours. I had an insurance company do a cholesterol test on me when I wasn't fasting and it was 75-100 points higher than a test done when I'd been fasting.
posted by randomkeystrike at 2:17 PM on May 13, 2011

I can't say what the average amount serum cholesterol levels go up after eating, because it completely depends on what you have eaten. The fact of the matter is, your body gets cholesterol from 2 separate sources: what you eat and what your body yourself makes. Understanding your serum cholesterol levels when you are fasting and after you have eaten can both be important, and if your cholesterol is consistently high, it would be greater cause for concern rather than if it were high only once. (I am not saying this as your medical doctor)

If you are concerned about your cholesterol, there are steps you can take to reduce it yourself-importantly, eating a low fat, low cholesterol diet. (The low fat part is important. You know those Lays potato chips that advertise no cholesterol content? Will still increase your cholesterol if they are high in fat. Why? Because your intestines will absorb the fat in the chips, and the fat in those chips will be packed into LDL along with cholesterol your body makes to finish "filling" the package). If you have high cholesterol consistently after fasting, this means your body is probably making too much. Here the solution involves your doctor prescribing drugs that inhibit your bodies ability to make or absorb cholesterol.
posted by nasayre at 3:45 PM on May 13, 2011

A long-term relationship between fat and cholesterol has hardly been proven. You can find plenty of advice that suggests a weak relationship or none at all. Not to mention cultures like the traditional Masai who eat tons of fat and have low cholesterol. Or the fact that mortality is lowest around 210-220 total cholesterol, even though the relationship is somewhat weak. Or that the mechanism for atherosclerosis is pretty well documented, and it relies on oxLDL and not cholesterol in general.
posted by Earl the Polliwog at 1:17 AM on May 14, 2011

Hi Earl the Polliwog,
Thanks for your comments, I enjoyed looking through your links, although I am not sure I can fully agree with the Dr. Guyanet's conclusions.

Evidence does in fact exist in the literature supporting the link between lipid intake and serum cholesterol levels. A quick search through pubmed comes up with a couple of articles that would support the opposite claim, that dietary lipid will affect serum cholesterol levels. In mice, Yu et. al show that a high lard-fat diet did increase serum LDL levels (To be fair, the lard fat diet did have somewhat higher cholesterol than traditional feed).

Valsta et. al present evidence from a retrospective study in Finland, in which a couple of thousand people were tracked over about 25 years. The decrease in serum cholesterol here was attributed to a lower-fat diet (again, to be fair, cholesterol in the diet also decreased, and the effect of lipid-lowering drugs alone was less profound on serum cholesterol, but there was an effect).

Mozaffarian and Willett performed a literature review and say that literature supports the claim that a diet high in trans-fatty acids causes LDL levels to increase, HDL levels to decrease, and ultimately leads to a significantly higher risk of coronary heart disease and death from heart attack.

In regards to the Masai, it is a great example of a people who have low cholesterol regardless of what they eat. On the flip side of the coin there are people who will have high cholesterol regardless of what they eat. The best example I can think of off the top of my head are those people with familial hypercholesterolemia. I point this out because it is very important to emphasize that a person's genes will have a huge role in whether or not they have high serum cholesterol levels.

Also, I need to clarify what exactly oxLDL is. It is oxidized-LDL. In other words, it is LDL that has been chemically modified, and is therefore somewhat more reactive and likely to stick in blood vessels. The simple fact of the matter is, if you have higher levels of LDL, you will have higher oxLDL, because oxLDL is derived from LDL. You can't really separate "cholesterol in general" from LDL (or other lipoproteins such as HDL, VLDL, etc), because the way that cholesterol is trafficked through your blood is within LDL. It can't float free in your blood.

Anyway, I don't claim to be the final authority on serum cholesterol levels, what is healthy and what is not. In truth, it is a very complicated picture. In the end, I think this is why a doctor will need to analyze all of a person's risk factors (including family history of heart disease, diet, lifestyle, etc) to determine whether a high blood LDL is really an issue.
posted by nasayre at 8:08 AM on May 14, 2011 [2 favorites]

Nice reply, nasayre. In interest of not threadjacking, I'll keep my reply as brief as possible, but we can discuss via PM if you like. The Yu study is in mice, who are less carnivorous than we. Not that it's useless, but not conclusive. The Valsta study, I can't access the full text, but it is just correlational rather than clinical. It is the case that for some people, dietary fat increases small LDL, but I'm not convinced that it is true for all. The Masai develop atherosclerosis when they stop their meat/milk diet, so regardless of cholesterol levels something seems protective about that meat and fat. oxLDL is indeed oxidized LDL and seems to be produced more from small-pattern LDL when high levels of easily oxidized polyunsaturated fats are present in lipoproteins, or there are high levels of sugar in the blood. Higher levels of small-pattern LDL would increase oxLDL formation as you say, so reducing small LDL is likely beneficial in most cases, as long as you're not screwing up something else in the process.
posted by Earl the Polliwog at 2:09 PM on May 14, 2011

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