From: km@speedy.cs.pitt.edu (Ken Mitchum)
Newsgroups: sci.med
Subject: Re: Smart Drugs
Date: 25 Aug 92 23:57:45 GMT
Reply-To: km@cs.pitt.edu (Ken Mitchum)
Organization: Computer Science Dept., University of Pittsburgh

In article <1992Aug25.005135.12844@seas.gwu.edu> sheryl@seas.gwu.edu (Sheryl Coppenger) writes:

>The question might be asked, though, when do doctors test and when
>do doctors treat?  What kind of neurological symptoms, for instance?
>Does B12 anemia look like iron-deficient anemia in the kinds of test
>for anemia that they would give at a blood bank, say?

I will leave it for Gordon to list all the neurological findings
associated with B12 deficiency. The most famous is posterior
column disease, manifested by gait and stability problems and
distinct findings on neurologic exam. The worst is dementia.

Anemias are classified in several ways, but the standard blood
count (CBC) gives enough information to hazard a guess as to the
type of anemia, if not the exact source. B12 and folate deficiency
both cause macrocytic (large RBCs) or megaloblastic anemia, manifested
by large RBCs with an MCV (mean corpuscular volume) greater than
100. Iron deficiency causes a microcytic anemia, with MCV below normal,
typically in the 60s or 70s. So, confusion of B12/folate deficiency
with iron deficiency would be rare, unless there were two types
of anemia present at the same time.

By the way, giving a patient folate will correct the anemia caused
by pernicious anemia, or any other B12 deficiency. But it will NOT
correct the neurologic problems. For this reason, one should never
order a folate level without a B12 level, or give folate to correct
a macrocytic anemia without first checking the B12 level. This is
a problem, as folate deficiency is MUCH more common than B12 deficiency,
and many more people are given folate than B12. It is a particular
problem in patients that self-medicate: folate (folic acid) is an
oral preparation present in many vitamin preparations, while the
B12 to correct deficiency must be given by injection, so that the
B12 in vitamin preparations will not correct virtually any B12
deficiencies (which are caused by malabsorption of B12, not low
dietary intake). Because of this, someone may mask the most obvious
findings of their B12 deficiency by correcting the anemia.

>
>Also, if the normal range is 200-800 (I forget the units of the test), does 
>that mean that it's valid for a doctor to see a reading of 201 and say 
>"you're normal" or 199 and say "you need shots"?  That's the kind of
>behavior that a lot of doctors show when they see test results.  It's
>pretty nonsensical, especially if you allow for test error and individual
>differences.  Not everyone is the classic "70 kg man".

B12 levels are not routine tests: if the test was ordered, then the
doctor would have some reason to suspect B12 deficiency. Given this,
borderline values are going to be treated as low values, and since
B12 is perfectly safe the patient with such a value would likely be
treated.

>doesn't mean much when applied to B12 deficiency.  Has anyone actually
>done a placebo test on B12 shots, say, on people who are in the low 
>"normal range" on B12 tests?  Or are you just spreading "old doctors'
>tales"? :-)

I don't know if anyone has studied the placebo effect of B12 injections,
but I would be surprised if someone hadn't. It is interesting that even
among patients who have pernicious anemia, they report an initial
sense of well-being and improvement after a B12 injection long before
any known physiological effect of B12 could take place, i.e. within
hours of leaving the doctor's office. Whether this is due to some
unknown action of B12, or to placebo influences, it unclear, but
very interesting.

>I'm not for giving "B12 shots all around", but it seems to me unlikely that
>there is some kind of binary "pernicious anemia"/"no pernicious anemia"
>switch in people or that everyone is going to be at their best at the
>same level.

Well, actually this is a binary thing! You either make antibodies to
parietal cells and intrinsic factor, or you don't. Normal people
don't make such antibodies. Now, in terms of "optimum" B12 level,
the "normal" values are statistical, so that some people with a level
of 250 may be deficient. That is why we don't just test people and
treat them blindly, but rather, in light of symptoms and findings.
If your level was 250 and you had findings consistent with B12
deficiency, I would treat you, even though your level was "normal."
But I wouldn't just march everyone through my office and give them
all B12 injections, which is what some physicians do.

 -km