Making sense of cholesterol tests
Time to get your cholesterol checked. Okay, but which test should
you get? It’s not so simple anymore. Here is a rundown of some
of the choices and their pros and cons:
Total cholesterol. This is the simplest and least
expensive test, and fasting isn't necessary. The test doesn’t require
any sophisticated lab work, either. The simple, do-it-yourself home cholesterol
tests measure total cholesterol. A reading of 200* or below puts you
in the desirable category; 200–239 is borderline high; and 240
or more is high.
But total cholesterol includes both “good” high-density
lipoprotein (HDL) cholesterol, and the “bad” varieties, chiefly
low-density lipoprotein (LDL) and very-low-density lipoprotein (VLDL).
So if your total cholesterol is in the desirable category, it’s
possible that you may have unhealthy levels of HDL (too low) and LDL
and VLDL (too high). Think of total cholesterol as a first glimpse, a
peek. Doctors are not supposed to make any treatment decisions based
on this number alone.
Cholesterol levels can be lowered by stress (physical or psychological)
or infection. An injury, stroke, or heart attack may have the same effect.
Sometimes the first sign of cancer is a dramatically lower cholesterol
reading. So if your cholesterol levels are unusually high or low, your
doctor will probably want to repeat the test some weeks later. Abnormal
readings may also lead to tests for other medical problems.
Total cholesterol and HDL. HDL wins its laurels as
the “good” cholesterol because it sponges up cholesterol
from blood vessel walls and ferries it to the liver for disposal. In
contrast, LDL deposits the harmful fat in vessel walls.
According to 2004 guidelines, an HDL level of 60 or above is protective
against heart disease, and below 40 makes you vulnerable to it.
The ratio of total cholesterol-to-HDL is important; the smaller the
number the better. For example, someone with a total cholesterol of 200
and an HDL of 60 would have a ratio of 3.3 (200 ÷ 60 = 3.3). If
that person’s HDL was low — let’s say 35 —the
total cholesterol-to-HDL ratio would be higher: 5.7.
Reports from the Framingham Heart Study suggest that for men, a total
cholesterol-to-HDL ratio of 5 signifies average risk for heart disease;
3.4, about half the average risk; and 9.6, about double the average risk.
Women tend to have higher HDL levels, so for them, a ratio of 4.4 signifies
average risk; 3.3 is about half the average; and 7, about double. If
you have a high level of total cholesterol, it may be less alarming if
your total-to-HDL ratio is low.
Cholesterol: The good and the bad of
HDL High-density lipoprotein
- Makes up 20%–30% of total cholesterol
- The “good” cholesterol
- Moves cholesterol from arteries to the liver.
LDL Low-density lipoprotein
- Makes up 60%–70% of total cholesterol
- Main form of “bad” cholesterol
- Causes build up of plaque inside arteries.
VLDL Very-low-density lipoprotein
- Makes up 10%–15% of total cholesterol
- With LDL, the main form of “bad” cholesterol
- A precursor of LDL.
LDL cholesterol. The LDL measurement
is usually considered the most important for assessing risk and deciding
on treatment. The definition of a healthy level keeps on getting lower.
Current guidelines say an LDL of 100 is “optimal.” In a revision
of the guidelines in early 2004, doctors were advised that an LDL of
less than 70 should be a “therapeutic option” for very-high-risk
patients. Some experts say that would be a healthy LDL goal for all of
Your LDL is computed by plugging the measurements for total cholesterol,
HDL, and triglycerides into a: LDL = Total cholesterol – HDL – (Triglycerides ÷ 5)
You have to fast for about 12 hours before the test because triglyceride
levels can shoot up 20%–30% after a meal, which would throw off
the equation. Alcohol also causes a triglyceride surge, so you shouldn’t
drink alcohol for 24 hours before a fasting cholesterol test.
Another important limitation: At a triglyceride level of about 250
or higher, the calculation becomes less reliable because dividing triglycerides
by a factor of 5 provides a less accurate estimate of VLDL.
The numbers to know
under 200 mg/dL
LDL (bad) cholesterol
under 100 mg/dL
HDL (good) cholesterol
over 40 mg/dL
under 150 mg/dL
C-reactive protein (CRP) is a protein in the blood that increases with
inflammation. Because atherosclerosis is fundamentally an inflammatory
process, many experts believe that CRP testing could lead to early detection
and therefore save lives. The American Heart Association says CRP tests
are warranted for people at intermediate risk for heart disease, but
not those at the low and high ends of the risk spectrum.
The current guidelines recommend a fasting cholesterol test every five
years for everyone beginning at age 20. A fasting cholesterol test gives
you the important numbers: total, LDL, and HDL cholesterol, as well as
triglyceride levels. If you have difficulty fasting or your triglycerides
are over 250, you are a candidate for one of the new tests that measure
LDL directly. But unless you’re a special case, sophisticated breakdowns
of the various cholesterol types will only give you a case of information
overload. Skip them and stick to the basics.
February 2005 Update
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