Which cholesterol test should you get?
cholesterol test should you get?
(This article was first printed
in the November, 2004 issue of the Harvard
Health Letter. For more information or
to order, please go to http://health.harvard.edu/health.)
The number of tests has
proliferated. But for most people, the traditional
fasting cholesterol is still the way to go.
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. Total
cholesterol doesn't vary much after you've
eaten, so you don't have to worry about fasting.
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 can
be misleading. It 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.
Incidentally, although eating
before the test doesn't affect total cholesterol
or HDL levels to any great extent, 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
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.
HDL also contains less fat
than LDL or VLDL. All these cholesterols are
actually small bundles of protein and cholesterol.
The cholesterol portion lowers the density
of the package, so low density means more cholesterol
and high density means more protein.
For the patient, there's really
no difference between getting a total cholesterol
and getting a total and an HDL cholesterol
test together. Total and HDL can be measured
using the same blood sample. Neither test requires
An HDL measurement is informative
by itself and, in relation to total cholesterol,
expressed as the total cholesterol-to-HDL ratio.
According to 2004 guidelines,
an HDL level of 60 or above is protective against
heart disease, and below 40 makes you vulnerable
Plug your HDL into the total
cholesterol-to-HDL ratio, and 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 that they're at average
risk for heart disease; 3.4, about half the
average; and 9.6, about double the average.
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
Many people with a high HDL
also have a low total cholesterol-to-HDL ratio,
so computing it may not add that much useful
information. But some clinicians like to use
it as an indicator of heart disease risk. And
if you have a high level of total cholesterol,
it may be less alarming if your total-to-HDL
ratio is low.
The good and the bad of it
- Makes up 10%-15% of total cholesterol
- With LDL, the main form of "bad" cholesterol
- A precursor of LDL.
- Makes up 60%-70% of total cholesterol
- Main form of "bad" cholesterol
- Causes build up of plaque inside
- Makes up 20%-30% of total cholesterol
- The "good" cholesterol
- Moves cholesterol from arteries
to the liver.
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 us.
The fasting cholesterol test
is the traditional way to measure the level
of LDL, but it doesn't measure LDL directly.
Instead, your LDL is computed by plugging the
measurements for total cholesterol, HDL, and
triglycerides into a formula called the Friedewald
equation (named for William Friedewald, who
developed it). This is the equation: LDL =
Total cholesterol - HDL - (Triglycerides ÷ 5)
Although triglyceride levels
can be significant by themselves, the triglycerides ÷ 5
quotient is included in the equation as a way
to indirectly calculate the VLDL level. So,
in essence, the Friedewald equation subtracts
your HDL and an estimate of VLDL from your
total cholesterol to get your LDL level.
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
Another important limitation:
At a triglyceride level of about 250 or higher,
the Friedewald equation becomes less reliable
because dividing triglycerides by a factor
of 5 provides a less accurate estimate of VLDL.
Direct measurement of LDL. Several
companies are marketing tests that measure
LDL directly rather than estimating it from
an equation. Direct LDL testing has become
popular in Florida and some other southeastern
states. They have two advantages. First and
foremost, you don't have to fast. Second, the
measurements are accurate even if your triglycerides
The chief drawback of the
direct LDL tests is their cost. If the testing
company does several other tests in addition
to LDL, the bill can climb into the hundreds
of dollars, and it may not be covered by your
insurance. The new wave of tests may also give
us more information than we can really use.
In fact, some experts see direct LDL testing
as a Trojan horse for more and more blood tests
that have little practical value. For example,
HDL can be broken down into HDL2 and HDL3.
Some studies suggest that HDL2 is more potent
and desirable. But, at this point, there is
no reason to know your HDL2 level.
Other calculations and
tests. If your triglycerides are between
200 and 500, your doctor may want to know
your non-HDL level and use that measurement
to guide your treatment. It's calculated
Total cholesterol - HDL =
Put another way, non-HDL cholesterol
is the sum of VLDL and LDL levels.
Non-HDL becomes a good predictor
of heart disease in people with high triglycerides
because as triglycerides increase, so do VLDL
levels, and VLDL (not just LDL) starts to play
a larger role in atherosclerosis.
Apolipoprotein B, usually
shortened to apo B, is a signature component
of LDL, VLDL, and other blood lipids that cause
atherosclerosis. Research has shown that there's
a strong relationship between apo B levels
and heart disease. Some experts argue that
the relatively simple test for apo B could
replace the increasingly complicated measurement
of cholesterol subtypes. The rebuttal: Both
doctors and patients have a lot of experience
with cholesterol testing that shouldn't be
abandoned for an unfamiliar test.
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. But there's also
concern that the CRP test is just piling on
more information and tests. For many, body
weight, family history, and HDL and LDL cholesterol
levels are just fine for assessing heart disease
risk and determining steps that should be taken
to reduce it. 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
should you do?
The current guidelines recommend
a fasting cholesterol test every five years
for everyone beginning at age 20. That's sound
advice. 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.
(This article was first printed in the November,
2004 issue of the Harvard Health Letter. For
more information or to order, please go to http://health.harvard.edu/health.)
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