Re: [Gnumed-devel] Measurements (was: New developer searching for a task)

[Hilmar Berger]

On 6 Dec 2002, Christof Meigen wrote:
> 
> - My general intention would be to leave the decision what value is
>   normal and what not to the doctor, based on the avaliable information
>   on the patient (age, diagnosis, smoker etc) and published norms.

Absolutely true. This decision is one of the basic medical tasks. Norms
are just hints to where a important change has happened.

>   I see that this is strongly against the intention of Labs, who
>   probably claim to be the only ones who know how to judge the things
>   they measured (and don't publish how they come to that judgement).
As far as I know labs have a much higher level of quality control as
single user-maintained devices. Usually labs take part in tests where
samples of precisely known composition are measured in a lot of labs at
one time to minimize inter-lab differences (in Germany called
"Ring-Versuche") and measure the deviation of a single lab. I'm not aware
of a similiar institution for single devices located at a general
practitioners office.
   
> - Imagine a doctor changes Labs, and a value of a patient is marked
>   abnormal, when the very same value two weeks ago was judged
>   'normal'. This _might_ be because the first lab measured with a 
>   different method (which for example has a larger error, so the
>   slightly abnormal measurement was still marked normal) but
>   it also might be because the first Lab just used a different
>   norm.
IMHO measuring a parameter as an (value, range) tuple and marking it as
abnormal are two different issues. 
You have to differentiate between 
a) a classification as normal/abnormal etc. by using norms and
b) classification as physiological/pathological or important/unimportant 
in relation to the state of the patient.

The latter can't be derived directly from the former but is an individual
decision of the particular physician.

> - Hm. On the one side, you have to be able to store and display the
>   test results (incl. judgement of normality) as they come from the
>   lab. On the other side, the doctor should perhaps be able to apply
>   more modern or more specific norms to the values. And of course,
>   judgements should be standardized (one might simply say
>   "normal/abnormal", the other provides a SDS-Value, the next one a
>   centile, and the third gives his own coding scheme?) ... so, while
>   the judgement by the Lab is static, the judgement by availiable
>   norms is dynamic data calculated from the norms and the value and
>   should not be stored
On the other hand it could be interesting to know what norm was used in
the process of evaluation a lab result. It might prove useful to store
this information (e.g. you used a different norm because you suspected a
certain illness that could be ruled out afterwards).

Hilmar