Significant differences in lab normal ranges
Halterb
understanding laboratory test results returned a great deal of information. One
of the elements which was new to me was that normal ranges at one lab may
differ from ranges at other labs, and that individual labs may tend to base
their ranges on their own experience with doing blood tests.
I looked back over my own tests over many years and noticed quite a
"progression" in normal ranges, and quite a variation in normals from one lab
to another recently--variations of as much as 10% or more, which seems quite a
bit to me. I also noticed hospital labs seem to be a little more conservative
in deviations from traditional ranges than other labs.
This raises several considerations. First, don't we almost have a
"self-fulfilling prophecy" type situation here? If a lot of people have rotten
diets and unhealthy lifestyle factors, then if we adjust normals to the general
population aren't we saying sub-optimal operating bodies are not only
acceptable but expected? Carried to its extreme, a highly fit person could
appear to be abnormal (which may be a sad commentary on today's society!)
For example (and one of my special interests), hemoglobin. The traditional male
range used to be 14-18. Now, one of my labs is happy with 12.8-17, over 10%
below the old low limit. That lab considers MCH to be 27.4-35 whereas the
hospital lab and the traditional range were 27-31; a person testing at 35 would
show normal at the lab with the high range, while a considerably high flag
would be raised by the other standard--and with a 12.8 hemoglobin (still normal
at the one lab) the other range would raise some question as to a slightly
anemic tendency and a macrocytic tendency possibly related to B-12 problems
which in turn may be associated with excessive restriction of red meat in the
current anti-cholesterol obsession or semi-vegetarian approach. I realize
discrepancies of this degree are not enough to attract special medical
attention, but in combination with symptoms and other observations may be
worthy of recognition.
Also, hgb related, I notice the MCV high range has risen greatly as well--at
the hospital lab to 96 and the other lab to 99 (from the old standard of 92),
again making acceptable an indication of larger cell size than in the past. And
the RBC range has dropped from 4.6-6.2 to 3.9-5.6. Is it the body which has
changed, or the "lowering of standards to reflect the least common
denominator"?
Maybe we need to raise the standards to encourage a higher level of national
wellness. It would be interesting to know how other countries handle this.
Sorry for the lengthy observations from an amateur, but hopefully, someone may
find the concept interesting.
Tami Evers
are actually taken FROM the population in that area, of seemingly NORMAL
healthy people.
Thats why the ranges will differ from time to time and by demographics.
Tami E.
http://www.meetandplay.com
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Graham Shepherd
<19990811104737...@ng-cq1.aol.com>...
Also, you have to take into account the fact that (1) the parameter you are
measuring may vary within an individual normally (eg glucose levels) over a
short period of time, (2) the tests are not always very precise (ie there
can be a spread of values if you test the same sample multiple times) and
(3) there is always some operator-dependent variation - ie 2 different
people doing the tests won't always get the same numbers. That's why you
need highly trained people to do the tests and interpret the results.
GS
Ken Robertson
>
> A person learns something every day! My original post asking for help
> understanding laboratory test results returned a great deal of information. One
> of the elements which was new to me was that normal ranges at one lab may
> differ from ranges at other labs, and that individual labs may tend to base
> their ranges on their own experience with doing blood tests.
>
which can be used as a comparison for the age, gender, ethnic group or
whatever. In general these ranges are based on 95% confidence limits and
so, where there is a normal distribution of results, 2.5% may be lower
than the range and 2.5% above. It is important to keep in mind that a
result may be "abnormal" but still in the reference range. (e.g. an
amylase which is usually 40 U/L goes up to 80 U/L. Still in the ref
range but double its original value.)
Variations in the specificity of a method, the type of instrument being
used and a number of other factors can also affect the final result.
> I looked back over my own tests over many years and noticed quite a
> "progression" in normal ranges, and quite a variation in normals from one lab
> to another recently--variations of as much as 10% or more, which seems quite a
> bit to me. I also noticed hospital labs seem to be a little more conservative
> in deviations from traditional ranges than other labs.
>
> ............ Carried to its extreme, a highly fit person could appear to be abnormal
> (which may be a sad commentary on today's society!)
No, they are not *abnormal*, they are only outside of the reference
range. It really means that in the ideal world, the lab would have a
separate reference range for the "superfit" tri-athletes, body-builders
etc.
Regards, Ken
Magilla
>A person learns something every day! My original post asking for help
>understanding laboratory test results returned a great deal of information. One
>of the elements which was new to me was that normal ranges at one lab may
>differ from ranges at other labs, and that individual labs may tend to base
>their ranges on their own experience with doing blood tests.
>
>I looked back over my own tests over many years and noticed quite a
>"progression" in normal ranges, and quite a variation in normals from one lab
>to another recently--variations of as much as 10% or more, which seems quite a
>bit to me. I also noticed hospital labs seem to be a little more conservative
>in deviations from traditional ranges than other labs.
>
>This raises several considerations. First, don't we almost have a
>"self-fulfilling prophecy" type situation here? If a lot of people have rotten
>diets and unhealthy lifestyle factors, then if we adjust normals to the general
>population aren't we saying sub-optimal operating bodies are not only
>acceptable but expected? Carried to its extreme, a highly fit person could
>appear to be abnormal (which may be a sad commentary on today's society!)
You're making the mistake of believing that there are such things as
fixed normal ranges. There is no such beast. A "normal" range is a lot
like a "normal" body shape - there's a lot of variation between
individuals and what's normal in one group may be abnormal in another.
I have been involved in the excercise of establishing normal ranges
for a laboratory and believe me it is no easy task. There are a lot of
variables unique to each laboratory and its method of testing. One of
the most difficult we found was CK (creatine kinase) -since its
dependant on muscle mass (among other things), the type of population
sampled is going to make an enormous difference. In our case the
results were further compromised by a large number of joggers and
gym-junkies with permanently elevated CK (one of our staff returned
from a day at the gym with a CK of 18,000 U/l -he was fine and levels
returned to "normal" within a few days).
Cholesterol is another problem analyte where "normal range" may be
quite different from the recommended range.
>For example (and one of my special interests), hemoglobin. The traditional male
>range used to be 14-18. Now, one of my labs is happy with 12.8-17, over 10%
>below the old low limit. That lab considers MCH to be 27.4-35 whereas the
>hospital lab and the traditional range were 27-31; a person testing at 35 would
>show normal at the lab with the high range, while a considerably high flag
>would be raised by the other standard--and with a 12.8 hemoglobin (still normal
>at the one lab) the other range would raise some question as to a slightly
>anemic tendency and a macrocytic tendency possibly related to B-12 problems
>which in turn may be associated with excessive restriction of red meat in the
>current anti-cholesterol obsession or semi-vegetarian approach.
I disagree with you here -B12 deficiency due to diet is quite rare in
western societies because the body stores of B12 are usually quite
high. It would take a prolonged (I'm talking years) period to deplete
a healthy person of their B12. It is only seen in the strictest of
vegetarians (not "semi-vegetarians" as you suggest). On the other hand
macrocytic anaemia due to folate deficiency -caused by a lack of green
leafy vegetables in the diet - is much more common.
Terry
analyzing. Different instrumentation reports values a little differently,
therefore the lab normal ranges may be set a little differently.
Halterb <hal...@aol.com> wrote in message
news:19990811075516...@ng-bk1.aol.com...
> A person learns something every day! My original post asking for help
> understanding laboratory test results returned a great deal of
information. One
> of the elements which was new to me was that normal ranges at one lab may
> differ from ranges at other labs, and that individual labs may tend to
base
> their ranges on their own experience with doing blood tests.
>
> I looked back over my own tests over many years and noticed quite a
> "progression" in normal ranges, and quite a variation in normals from one
lab
> to another recently--variations of as much as 10% or more, which seems
quite a
> bit to me. I also noticed hospital labs seem to be a little more
conservative
> in deviations from traditional ranges than other labs.
>
> This raises several considerations. First, don't we almost have a
> "self-fulfilling prophecy" type situation here? If a lot of people have
rotten
> diets and unhealthy lifestyle factors, then if we adjust normals to the
general
> population aren't we saying sub-optimal operating bodies are not only
> acceptable but expected? Carried to its extreme, a highly fit person could
> appear to be abnormal (which may be a sad commentary on today's society!)
>
male
> range used to be 14-18. Now, one of my labs is happy with 12.8-17, over
10%
> below the old low limit. That lab considers MCH to be 27.4-35 whereas the
> hospital lab and the traditional range were 27-31; a person testing at 35
would
> show normal at the lab with the high range, while a considerably high flag
> would be raised by the other standard--and with a 12.8 hemoglobin (still
normal
> at the one lab) the other range would raise some question as to a slightly
> anemic tendency and a macrocytic tendency possibly related to B-12
problems
> which in turn may be associated with excessive restriction of red meat in
the
M
between labs is mainly due to their sample selection for defining the range.
Labs are required to use a sample of at least 20 specimens from a healthy or
normal population to define this range for each test. Larger labs usually
use much larger samples. So the difference between labs is mostly due to
different sample sizes, small sample sizes (usually 20), and the subjective
nature of rejecting specimens from individuals who are deemed abnormal. Most
small labs will compare their results to those published for large labs to
make sure they are not too far out of line.
For most tests, however, these differences between lab ranges are not
important, since a test result must fall far outside the range to affect
treatment.
Halterb wrote in message <19990811075516...@ng-bk1.aol.com>...