I have worked in microbiology for most of my 33 years in the business.
I'll defer these technical questions to my chemistry colleagues.
From what I remember, the triglyceride procedure measure endogenous
triglycerides. If you do not fast long enough, the procedure will
measure both exogenous (from your last meal) and endogenous. The doc is
only interested in endogenous (what your body is actually producing, not
from the Big Mac you ate for dinner).
I have never performed triglyceride testing (or any other cardiac risk
procedures), as I only worked chemistry briefly on second shift. Trig's
were a batched day shift procedure when I worked in chem, and I only
worked part time. This was many years ago.
It's been many many years since I studied this stuff, as I now work in
micro on a daily basis, and have not worked in any other department
since 1988. Hopefully the chem people will set me straight if I'm
incorrect.
I also don't know if labs automatically use the calculated LDL levels
unless the doc actually orders the quantitative one - there are
compliance issues with medical insurance. This means that the lab cannot
do or charge for any test not ordered by a physician. I'm not sure if
LDL comes under this or not, or if there are other determining factors
that decide when an LDL is calculated or determined directly.
Judy Dilworth, M.T. (ASCP)
Microbiology
> Maybe someone with all that training can tell me,
> If I plot a graph of Triglycerides against Time after a heavy meal, what
[quoted text clipped - 13 lines]
> The lab that provided my results calculated my LDL even though my TG was
> 222.
> Someone here recently indicated (if I interpreted it correctly) that the
> formula
[quoted text clipped - 4 lines]
> The lab that provided my results calculated my LDL even though my TG was
> 222.
My lab cancels the calculation if the trig is greater than 400. I don't
know where the other numbers came from. We also offer a direct LDL
which we run when the calculated is canceled or if the patient is not
fasting.

Signature
John Gentile
Editor
Rhode Island Apple Group
> > We are trained to do this through comprehensive schooling
> > that, for MT's, occurs after college in approved schools of medical
[quoted text clipped - 13 lines]
> kind of curve would I expect to see?
> Linear, exponential, S-Shaped ?
It has been a while for me as well, so chem techs PLEASE correct me if any
info is incorrect. If I remember correctly, the curve should be bell
shaped, with peak levels occurring at about 4 hours post-ingestion, and
normal clearance at about 8 hours (though really high-fat meals can take
longer to clear). Levels will vary depending on caloric content and type of
food ingested. I would suggest that you get a good biochemistry book that
goes over this and educate yourself. Lipid metabolism is complicated and
has a great number of variables which makes me leery of providing anything
resembling a simple answer.
> "fasting 12-14 hours" does not sound like a very scientific procedure to me.
> How does individual metabolism affect Triglyceride levels?
> I did fast 12 hours, and my TG was 222.
What do you mean, not very scientific? There was research aplenty done to
determine the amount of time most people need to fast to obtain a baseline
triglyceride level. If you fasted (and that means NOTHING but water for
those 12 hours), then the result you received is scientifically valid.
> Someone here recently indicated (if I interpreted it correctly) that the
> formula
> LDL = Total Cholesterol - HDL - (Triglycerides divided by 5)
> should not be used if the TG is over 150 or if the calculated LDL is under
> 100.
I believe that the general normal range (this is GENERAL and NOT to be
specifically applied to any lab or instrumentation) is below 150mg/dL, and
it is at about 400 mg/dL that the trig is too high to effectively utilize
the equation. John G., my lab also uses 400 mg/dL as the cutoff point for
calculated vs. direct LDL. Our lab also performs a direct LDL any time a
physician orders it... which leave the physician with the responsibility of
knowing the patient's history and current condition, and utilizing that
knowledge to order the LDL test appropriate for each patient. Methodologies
for Direct rather than calculated LDL have not been refined enough to be
widely clinically utilized until the last few years (anyone have a better
grasp on the time frame for this?), if I recall. I think that in time, as
shown by ongoing and recent research, that eventually as direct LDL
methodologies become widespread, that this will become the choice method of
measurement rather than a calculated result. Please see the listed article
for more information, but remember that this is ONE study, that was
published in 2004, so is quite recent. All good "scientific procedures"
should be reproducible. Your biochem research should include information on
the scientific method to help you understand why one study doesn't write the
law.
http://www.medscape.com/viewarticle/468792_print
> The lab that provided my results calculated my LDL even though my TG was
> 222.
I would suggest calling the lab that performed your test and asking what
their cutoff value is for reporting a calculated LDL.
Thanks to all chem techs in advance for making sure my info wasn't more
mental cobwebs than good information.
Shylirin
Robert - 04 Nov 2005 08:10 GMT
"Shylirin" <shylirinsplinter@cox.net> wrote in message
> for Direct rather than calculated LDL have not been refined enough to be
> widely clinically utilized until the last few years (anyone have a better
> grasp on the time frame for this?), if I recall. I think that in time, as
> shown by ongoing and recent research, that eventually as direct LDL
> methodologies become widespread, that this will become the choice method of
> measurement rather than a calculated result.
We are already doing LDL directly on all specimens. It offers the advantages
on the new platform instrument vs the old one in which a manual pretreatment
separate procedure is undertaken to precipitate out and leave HDL. The
increase labor is not worth it so direct methods without manual handling is
the preferred way to go with both HDL and LDL.
There are differences in the direct LDL in low lipid specimens compared to
the calculated methods.
Shylirin - 05 Nov 2005 04:25 GMT
> "Shylirin" <shylirinsplinter@cox.net> wrote in message
>
[quoted text clipped - 13 lines]
> There are differences in the direct LDL in low lipid specimens compared to
> the calculated methods.
Nice! I haven't run a Direct LDL myself in about 7 years (just read the
articles now), but I do remember it was time-consuming. What platform are
you running? Our main hospital lab runs the Aeroset (for about 3 years now)
and I think this is what they are using for the Direct LDL.
Robert - 05 Nov 2005 08:52 GMT
> > "Shylirin" <shylirinsplinter@cox.net> wrote in message
> >
[quoted text clipped - 23 lines]
> you running? Our main hospital lab runs the Aeroset (for about 3 years now)
> and I think this is what they are using for the Direct LDL.
The Abbott Architect allows for immunochemistry and regular chemistry
processing including iron binding by simply loading the specimen. The
linearity for the trigs is up to about 1400 and the LDL linearity is
6.6 -992 mg/dl.
Samples with a high Trigs does not interfere with the LDL determination or I
should say up to about 1300 mg/dl.