Ratinale for NPO order prior to routine blood work?

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Jan - 07 Jun 2007 09:16 GMT

"NPO after midnight" seems to be a standard order when blood work has
been ordered for the following morning. I am wondering what the
rationale is in so far as importance of a specific number of hours is
concerned.

If the blood is to be drawn at 6am, 8am, 11am, or 11am the number of
hours of fasting varies from six to eleven hours. If we assume most
tests would not be given until at least 8am it can be assumed in most
cases the period of fasting would be at least eight hours.

My question occurred to me after thinking about why a person getting a
late morning test (11am) would be required to be fasting for a longer
period of time than one having an early morning test (8am).

Common sense suggests the person receiving the late morning test
should be allowed to eat or drink for three hours longer than the
person having the early morning test.

Is there a web site that explains this subject in more detail?

Thanks.

Jan

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Manky Badger - 07 Jun 2007 10:02 GMT

> "NPO after midnight" seems to be a standard order when blood work has
> been ordered for the following morning. I am wondering what the
[quoted text clipped - 15 lines]
>
> Is there a web site that explains this subject in more detail?

"NPO" - don't know that one ?

When a patient fasts overnight for a blood test (which isn't THAT often),
that venepuncture is (should be) done as the first one of the morning. If
someone fasts overnight and blood isn't drawn until 11am, then what's going
on?

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Jan - 10 Jun 2007 12:58 GMT

> > "NPO after midnight" seems to be a standard order when blood work has
> > been ordered for the following morning. I am wondering what the
[quoted text clipped - 22 lines]
> someone fasts overnight and blood isn't drawn until 11am, then what's going
> on?

That's what I wondered too!!!

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John Gentile - 09 Jun 2007 03:50 GMT

> "NPO after midnight" seems to be a standard order when blood work has
> been ordered for the following morning. I am wondering what the
[quoted text clipped - 19 lines]
>
> Jan

There are few lab tests that require fasting. As a general rule,
fasting for a lipids test that includes triglycerides should be for 12
to 14 hrs. Fasting for a fasting glucose should be for 8 hours.
There is no need to fast for other common lab tests, even for a
cholesterol (without trigs).

Signature

John Gentile MS, M(ASCP)
Laboratory Information Mgr.
VA Medical Center
Providence, RI
yjgent@cox.net

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Jan - 10 Jun 2007 13:24 GMT

> > "NPO after midnight" seems to be a standard order when blood work has
> > been ordered for the following morning. I am wondering what the
[quoted text clipped - 32 lines]
> Providence, RI
> yjg...@cox.net

Thank you, John. That is what I thought too, and since they had plans
to do a full work-up, lipids included, everything I could find in
books around the house, especially Todd & Sanford (17th ed., 1984)
suggested to me they should have told me "nothing by mouth" after
8:45pm in preparation for a 10:45am test. That is why I found the "NPO
after midnight" so confusing. There was nothing in Todd & Sanford (or
any site I googled that provided a rationale for a 10 3/4 hour fast.
The "rule" seemed to me to be, as little as 2 to 6 hours for some
tests, 8 hours for most, and 12 to 14 for lipids tests. That is why I
decided to ask here. I was surmising that lab technologies had
improved sufficiently since 1984 that a 12 to 14 hour fast for a
lipids profile was found to be too much time. I just couldn't find it
in print and I didn't have time to drive 35 miles downtown to the
medical library to see if a more recent Todd & Sanford was more on
point than the old edition I picked up on the cheap at a local Friends
of the Library sale (just thinking it might be interesting reading).
That is why I decided to post here ... knowing that millions of people
read Usenet groups -- so I figured I would get an accurate timely
answer here (albeit not as fast as I could have obtained if I had a
current Todd & Sanfords, "Clinical Diagnosis and Management by
Laboratory Methods," rather than an edition 22 years old).

Thanks again for supporting the info I read. I guess the only
supposition one can make is that the doctor's office erred when then
said "nothing by mouth" (NPO) after midnight. Knowing a lipids profile
was to be done they should have said NPO after 8:45pm. I guess people
just repeat what they hear and think one standard is good across the
board regardless of the type of test to be given. I questioned that
rationale so that's why I asked.

Jan

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JEDilworth - 11 Jun 2007 05:22 GMT

The doctor's office should have said that a 12-14 hour fast was required
but that you could drink water. Water will not interfere with lipid
testing. Water does NOT mean coffee, pop, or anything but just plain
water.

NPO, per wikipedia, means this:

a.. Nil per os (NPO), Latin for a medical instruction meaning to
withhold food and fluids from a patient for various reasons, a shorthand
medical term that means "nothing by mouth"

I personally think that this the doc's office is used to issuing this
order before surgery, as many times the patient is NPO after midnight
for morning surgical procedures.

Seems to me that the 12-14 hour rule has something to do with endogenous
triglycerides vs. exogenous triglycerides. It takes 12-14 hours for
exogenous triglycerides to clear the serum (those ingested with your
previous meal). I think that is why there is a long wait before blood
can be drawn for true lipid profile results.

http://ajpgi.physiology.org/cgi/content/abstract/248/2/G164

Here are Labcorp's requirement for triglyceride testing:

http://www.labcorp.com/datasets/labcorp/html/chapter/mono/pr008600.htm

Judy Dilworth, M.T. (ASCP)
Microbiology
(used to do chemistry a long time ago)

> Thank you, John. That is what I thought too, and since they had plans
> to do a full work-up, lipids included, everything I could find in
> books around the house, especially Todd & Sanford (17th ed., 1984)
> suggested to me they should have told me "nothing by mouth" after
> 8:45pm in preparation for a 10:45am test. That is why I found the "NPO
> after midnight" so confusing.

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Manky Badger - 11 Jun 2007 17:57 GMT

> Thank you, John. That is what I thought too, and since they had plans
> to do a full work-up,

At the risk of sounding somewhat pedantice, the phrase "a full work-up" is
rather meaningless.
What exactly does it mean?

All I can imagine is that there is the intention to do every test known to
science in the hope of finding something wrong which isn't how medicine is
practiced (or is it?)

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GS - 11 Jun 2007 20:27 GMT

>> Thank you, John. That is what I thought too, and since they had plans
>> to do a full work-up,
[quoted text clipped - 6 lines]
> science in the hope of finding something wrong which isn't how medicine is
> practiced (or is it?)

I have sometimes thought (in my darker moments) that the purpose of
laboratory tests is simply to delay the onset of treatment until the patient
has recovered enough to withstand it....

GS

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Manky Badger - 13 Jun 2007 08:08 GMT

> I have sometimes thought (in my darker moments) that the purpose of
> laboratory tests is simply to delay the onset of treatment until the
> patient has recovered enough to withstand it....

Funny you should say that.......

A little while ago my mate's wife gave me a load of grief about how long her
tests would take. The G.P. sent off her bloods and told her to come back to
him in a month and implied that was how long the test would take.
We'd actually done all the tests that had been requested within four hours
of the blood being taken.

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