From: David Rind <drind@caregroup.harvard.edu>
Newsgroups: sci.med
Subject: Re: ate before a  "fasting" blood test --- how worthless will my
Date: Sat, 14 Aug 2004 22:02:41 -0400
Message-ID: <cfmg4h$nqi$1@reader1.panix.com>

Griffin wrote:
> On 2004-08-13 23:44:16 -0400, tariq.1.rahim@spamgourmet.com (tariq
> rahim) said:
>
>> absentmindedly had breakfast a couple hours before having a fasting
>> blood test for total lipid profile and liver function.
>>
>> will my results for cholesterol be totally distorted?  if so, will
>> they be extremely high? thanks.
>
>
> No telling, but they certainly won't represent interpretable fasting
> values, which are what your doctor asked for. Specifically, glucose and
> triglycerides will be falsely elevated...but there's no point guessing
> how high. You'll now have what we call a random blood glucose and random
> cholesterol...much less useful.

Depends on the background situation for why the test was being done. The
combination of liver function tests and a lipid profile sounds like this
may be testing in the situation of taking a statin, in which case it's
likely that someone really wants an exact LDL cholesterol level, and so
the non-fasting lipid profile won't be very useful.

If this is just a routine screening test, though, the situation is
different. The total cholesterol and HDL cholesterol are not changed
much by eating. The triglyceride level will be falsely high and the
calculated LDL cholesterol falsely low and so both are hard to
interpret. However, pretty often you can know from the total and HDL
cholesterol numbers and other risk factors whether the LDL cholesterol
could possibly be high enough to require any lifestyle modifications or
medication. If there's no chance it could be high enough to matter, then
the non-fasting numbers turn out to be useful.

--
David Rind
drind@caregroup.harvard.edu

From: David Rind <drind@caregroup.harvard.edu>
Newsgroups: sci.med
Subject: Re: ate before a  "fasting" blood test --- how worthless will my
Date: Sun, 15 Aug 2004 14:45:10 -0400
Message-ID: <cfoas7$ap8$1@reader1.panix.com>

Griffin wrote:
> Maybe, but the nonfasting labs will only be worthwhile if they're
> stone-cold normal. If they're high, I'm sending the patient back to the
> lab (after explaining again what "fasting" means).  :-)

The doctor certainly needs to know that the test was not done fasting,
since the LDL level will be falsely low and so may appear "okay" when
it's really high.

That said, if the results came back (and I've certainly seen this
happen) with a total chol of 220 and an HDL of 70, you can be sure that
the real LDL can't possibly be higher than 150. So if this is being done
for screening in someone with no other cardiac risk factors, there's
really no urgency to repeat the lipid profile for several years.

--
David Rind
drind@caregroup.harvard.edu