Hi, everyone,
My name is Phalevi. I'm a french medical student interested in
distal myopathies and of course dysferlinopathies. (so be lenient
with the english language :-))
In fact, I'm a general practitionner, not an expert in neurology nor
muscle disorders but I'm willing to learn from all of you.
One of my great inspiration is the creator of this site-group who
is "THE" dysferlinopathies real expert, Brad ( Salut Brad, pardon de
t'envahir mais cela me démangeait de réagir sur les CPK :))
As a clinician, my experience about CPK is more general. I just
wanted to add some remarks I noticed in my daily practise to
illustrate the non specifity of that test to a muscular dystrophy.

CK means Creatin Kinase aka Creatin PhosphoKinase CPK (term used in
France). It's an intracellular enzym which is present for most of the
part in the muscle, skeleton muscle ( fraction called CPK MM), heart
muscle (fraction called CPK MB) but also in brain tissue (fraction
called CPK BB).
The function of this enzym is to release the energy necessary for the
muscle to contract, from a chemical reaction with an energy storage
protein in the muscle, the creatin phosphate. .
If, for any reasons, the muscle cells are damaged, as Brad said, the
enzym will leak into bloodstream.
The blood test reflects the 3 fractions and could be considered as a
marker of a muscle suffering.
The CPK increase is the "calling sign" of a muscle damaging
process, which should lead to more precise investigations, specific
to a disease.

Even in sane people, CPK is released in blood because in normal
muscle tisssue, some cells will end their life and others will begin.
The normal rate depends on the different methods used by
laboratories. If you pay attention to your blood tests, they usually
give you the normal values as reference.
For information I can give the normal rate N of CPK
in "international unit = UI Unité Internationale" we use in my
country.
Male N: 0 - 195 UI /l
Female N: 0 - 170 UI /l

The interpretation of a pathologic CPK rate is
1-always compared to the normal rate, 2N, 5N, >10N etc...because we
know that such or such muscle pathology tend to have xN
2-always confronted to the clinical signs and the other complementary
exams. (other muscle enzyms, scan, RMI, EMG, muscle biopsy...)

High rate of CPK has numerous causes and the main indications of this
blood test in practise are:
1- a pain chest because a raise of the CPK MB fraction is suspect of
a heart stroke.
2- all muscle symptoms, pain, fatigue, atrophy, hypertrophy,
stiffness, soreness, cramp....leading to explore myopathies,
inflammatory or viral myositis, neuromuscular dystrophy...
3- traumatisms with bruises, during accident, or during a violent
physical effort.
4- the use of anticholesterol drugs, some antibiotics or vaccines
which could give muscle suffering.
5- sometimes, in meningitis (CPK BB), cerebral vascular stroke, some
cancers, hypothyroidism.

From my POV, this test is an instant reflect of a muscle suffering
state. It can't be related to a specific muscular disease
but it could help or guide to a diagnosis. Considering it as a
pronostic, or a severity factor, is more than debatable. In the other
hand, when new treatements are experimented it could be an
interesting marker of efficiency and surveillance.