55 - Creatine Kinase (CK)

KYJ 55 - CK creatine kinase.
In our KYJs (knowing your jargon), we explore terms you hear at work, but don't always understand.
Today is a blood test value called CK or creatine kinase.

First let's look at the word. 'Creatine' , it looks like 'create' and that is what it does.  Creatine is an organic acid made from nitrogen.  Muscles, being protein, are highly nitrogenous, and as muscle cells need a very high production of energy, creatine is needed in a reaction with the chemical that functions as cellular energy.  We covered in out cell biology video.
Do you remember the name of the energy?  Adenosine triphosphate (ATP).
So creatine is abundant in muscle cells.

Creatine is enzymatically broken down by an enzyme called a kinase.  After being acted on by CK, it binds with a phosphate molecule. It is then referred to as phosphocreatine

Our subject today is that enzyme. Creatine Kinase = CK.

CK or more correctly CPK, is creatine phosphokinase, an enzyme that is secreted by cells to create a chemical reaction between Creatine and ATPinto its waste byproduct called creatinine...this is excreted via the kidneys.    Note how similar these two words are.

In different tissues there are different types of creatine kinase  Cardiac tissue has a CK with two sub categories.  CK-M, and CK-B.  Together these CKs are released when heart muscle tissue is injured.  For this reason, a blood test called CK-MB was once used to diagnose MI, but due to insensitivity, it has been replaced by Troponin testing.

So normally CK is found in blood between 60 - 175 units/L.
It is elevated in any injury to muscle (MI, Rhabdomyolysis) where it is most abundant.

There is also elevated CK in patients with Thyroid dysfunction (low Thyroxine) .  It therefore has value in monitoring patients with Hypothyroidism. One study talked about Anticholesterol drugs like Lipitor (Statins) having links to raised CK.

In patients with alcoholic liver disease /failure, the CK can be low.

So there you have it. CK is an enzyme that catalyses a reaction between ATP and Creatine, to form creatinine that gets excreted in urine.