Reliability of derived-LDL formula
JT626
Is the above an accurate formula?
Is there any other way to measure/compute LDL?
And what is the significance of VLDL ?
Thanks.
David Rind
For this calculation to work, the triglycerides must be measured on a
fasting sample.
LDL can be measured directly, but nearly all the studies of LDL have
used the calculated LDL. So even though the calculated LDL is not
identical to the measured LDL, we know much more about the implications
and clinical management of the calculated LDL.
--
David Rind
dr...@caregroup.harvard.edu
LC
> LDL = Total Cholesterol - HDL - (Triglycerides divided by 5)
All clinical formulae and ratios are subject to certain limitations, and
this one is no different. Direct LDL measurements yield slightly different
numbers, but are subject to their own limitations and are more expensive.
The formula works well for most fasting individuals and is useful for
following people on therapy or lifestyle changes. However, if TGL is high
(ie, >400), the calculation might yield a negative number and is reported as
a comment instead of a number.
Robert
"LC" <Lcs...@juno.com> wrote in message
news:5k%7f.182858$qY1.1...@bgtnsc04-news.ops.worldnet.att.net...
>
> > LDL = Total Cholesterol - HDL - (Triglycerides divided by 5)
>
> All clinical formulae and ratios are subject to certain limitations, and
> this one is no different. Direct LDL measurements yield slightly
different
> numbers, but are subject to their own limitations and are more expensive.
Not nesesarily more expensive. The VAP is about as expensive as a regular
lipid panel of under $50 with Lp(a) included as well as particle size.
The origins of the formula which is a fudge factor for guessing what the LDL
is came from ultracentrifugation and working backwards.
Friedewald never intended for his equation to to calculate LDL in persons
with TG's over 150 mg/dl. Clini Chem 1972, 18:285-289.
In 2001 the ATP III recognized this fact and called for "further evaluation"
in persons with elevated TG's as defined as TG over 200 mg/dl. One can argue
further evaluation meaning a direct measurement technique.
The ratio of TG to cholesterol is not constant in VLDL particles,
particularly in persons with small/dense VLDL very atherogenic remnants. The
prevelance of metabolic syndrome and diabetes renders reliance of the
calculated LDL questionable in this setting.
The other problem is that the equation was never intended for use in persons
with calculated LDL's below 100 mg/dl, the new target level for high risk
persons. The equation is up to 18.5% falsely low when the actual LDL
calculated is below 100 mg/dl.
Directly measured LDL is being used in recent clinical trials.
HATS, the Heart Protection Study, PEPI and others have used directly
measured LDL.
Any formula that can give negative numbers in clinical settings is really
not very good. I have seen this with low TC in the 50 range and TG in the
150 range.
I see the problem similar to the calculated free thyroxine index T7 and the
measured one. Calculated ionized calcium vs measured and on and on.
Arguments were given in favor of both but eventually directly measured
analytes always win out.
>
> The formula works well for most fasting individuals and is useful for
> following people on therapy or lifestyle changes. However, if TGL is high
> (ie, >400), the calculation might yield a negative number and is reported
as
> a comment instead of a number.
Too many problems with calculations, based on the fact that directly
measured LDL was not very practical at the time, they were ignored.
We are running directly measured LDL on the Architect Abbott.
JT626
> JT626 wrote:
> > LDL = Total Cholesterol - HDL - (Triglycerides divided by 5)
> >
> > Is the above an accurate formula?
> > Is there any other way to measure/compute LDL?
> >
> > And what is the significance of VLDL ?
> >
> > Thanks.
>
> For this calculation to work, the triglycerides must be measured on a
> fasting sample.
If I were to plot Triglycerides against Time in hours (after a heavy meal),
would I see a linear graph with a negative gradient?
Or an L-shaped curve(like 1/x) ?
Or an S-shaped curve?
How does individual metabolism affect Triglycerides?
Would the rate of decrease in Triglycerides for a 14-year old be sharper
than for a 74-year old?
i.e. would someone with a very slow metabolism need to fast much more than
12-hours to get a meaningful Triglyceride measurement?
Someone here said that "treatment goals are based on LDL levels and the
total cholesterol is meaningless".
So, is LDL being calculated by the labs from a meaningless measurement?
I paid about $100 for my cholesterol test, and I see that the lab report
says "CALC" after the LDL reading.
Is the calculated LDL being reported to doctors, who use that to determine
treatment?
Since my TG was 222, should the calculated LDL not be used to determine
treatment?
David Rind
I don't know the answer to many of the questions above. However:
1) If the LDL was calculated from a nonfasting sample it is falsely low.
2) Total cholesterol isn't "meaningless" but it isn't the number that is
used to guide treatment.
--
David Rind
dr...@caregroup.harvard.edu