physiology

Creatine kinase - Creatine phosphokinase (CK or CPK)

Generality

Creatine kinase (CK) or creatine phosphokinase (CPK) is an enzyme found primarily in skeletal muscle tissue and cardiac fibers.

Its main task is to "facilitate" some chemical reactions that take place physiologically in our body. More in detail, creatine kinase allows the conversion of creatine into phosphocreatine, so as to consume ATP and generate highly exploitable energy .

What is ATP?

ATP stands for Adenosine Triphosphate. It is an important molecule, capable of supplying useful energy to almost all cellular functions. Furthermore, it can donate a phosphate group to other molecules. With this particular mechanism, called phosphorylation, our body can perform any type of cellular task, ranging from chemical / mechanical work to transport.

Creatine kinase has a dual function: if on the one hand it transforms creatine into phosphocreatine, on the other it is responsible for the reverse reaction. This results in the fact that from one side the enzyme makes the energy available and the other stores the same. In both cases, however, we need a little help represented by Magnesium.

Changes in creatine kinase levels are detectable through a simple blood sample .

In many cases, the CK test is required from the emergency room in the presence of suspected heart attacks, but it can be a simple routine examination when taking certain drugs or in the presence of kidney damage.

The presence of a high creatine kinase value can be due to heterogeneous causes, including fatigue (eg intense sports training), muscle diseases (such as dystrophy) or myocardial infarction.

What's this

Creatine kinase (CK), also called creatine phosphokinase (CPK), is an enzyme found in various tissues and cells in the body, especially in skeletal and cardiac muscle fibers. With its action, creatine kinase catalyzes both the conversion of creatine to phosphocreatine and the reverse reaction.

In the first case (arrow to the left) energy is stored, while in the second (arrow to the right) energy is released rapidly. In the course of intense and short-term physical exercise, creatine phosphate (or phosphocreatine) - accumulated during rest - transfers its phosphate group to ADP, synthesizing new ATP and thus providing new energy for muscle contraction.

For both reactions the presence of magnesium is necessary, which, by complexing with the ATP or ADP, acts as an activator:

MgADP- + PCr 2- + H + ↔ MgATP2- + Cr

Since creatine kinase is present in large quantities in muscle fibers, an increase in its concentration in the blood often indicates damage to skeletal or cardiac muscle.

Thanks to the three different isoforms of creatine kinase present in the human body, doctors are able to understand at what level the damage has occurred, distinguishing - for example - a myocardial infarction from the damage caused by muscular dystrophy.

  • CK-MM : constitutes about 98% of muscle creatine kinase and 70-80% of cardiac creatine kinase;

  • CK-MB : prevails in cardiac muscle, constituting 20-30% of myocardial creatine kinase and only 1-3% of skeletal muscle CK;

  • CK-BB : is present in brain tissue.

In the presence of cardiac necrosis, the CK-MB values ​​increase by the third - sixth hour from the beginning of the symptomatology, reach the peak around the 18th - 22nd hour and return to normal values ​​after 2 or 3 days.

Alterations in the CK-MB / CK-MM ratio are observed early, even before the CK-MB values ​​exceed the normal limits. The analysis of the various forms of creatine kinase is also useful for monitoring the effectiveness of the thrombolytic intervention, since, following tissue reperfusion, within 15-30 minutes a further circulation of the isoforms accumulated in the myocardial area can be observed injured.

In sport, an increase in creatine kinase is typical of stress rhabdomyolysis which accompanies unusual or particularly intense exercises, during which small lesions occur at the muscular level.

Why do you measure

The measurement of the amount of creatine kinase (CK) present in the blood allows the detection and monitoring of inflammation (myositis) or serious muscle damage, including cardiac damage .

In the presence of a suffering of the muscle, in fact, increased amounts of CK are released into the blood within a few hours. Creatine kinase concentration peaks between 12 and 24 hours and returns to normal after 2-4 days. If further damage occurs, CK concentrations can remain high; this aspect makes the CK test useful for monitoring progressive muscle or cardiac damage.

Even in the opposite case, that is if the levels of the CK were to be too low, it is essential to look for the causes of the imbalance.

Muscles, skeleton or heart?

The causes that determine alterations of creatine kinase values ​​can be different.

For this reason, it is important to evaluate the quantity of the different CK isoforms to understand where the damage really lies:

  • CK-MM : refers largely to muscle tissue, but is found in a fairly significant percentage also in the heart (about 70%); in principle, this isoform indicates a possible muscle fatigue or a minor tear.
  • CK-MB : if it is very high, it is likely that there has been a major heart attack or heart damage; in fact, this isoform is found in large quantities in the heart and to a minimum extent in the musculoskeletal tissue;
  • CK-BB : it is present exclusively in the brain tissue and in the lungs; however, this form is not easily detected in the blood.

When to take the exam?

  • Your doctor may prescribe the creatine kinase test when you suspect that some symptoms, such as fatigue, muscle pain and / or dark urine, are related to muscle damage.
  • The exam can also be indicated to monitor the resolution of pathologies associated with muscle damage or their persistence.
  • In some cases, then, the amount of creatine kinase (CK) in the blood can provide an indication of heart damage, which occurs due to a heart attack (although in this sense it has been largely replaced by troponin ). The CK test is also useful after the diagnosis of heart attack, to monitor the progression of the damage.

Finding false positives undergoing this analysis is frequent. Therefore, it is advisable to repeat the analyzes at least three times (spaced by a month) to verify the veracity of the result obtained.

Normal values

Creatine kinase normal values ​​are not easily identifiable, as they can be influenced by various factors, including age, sex, muscle mass and quantity / quality of physical training.

However, these are usually in the range 60 - 190 U / L.

The amount of CK that is normally found in the blood comes mainly from skeletal muscle.

High creatine kinase - Causes

Any pathology that causes muscle damage and / or interferes with the production of muscle energy or its use can cause an increase in creatine kinase.

Among the causes that determine the increase in CK are:

  • Physical efforts;
  • Alcohol abuse;
  • Muscular trauma;
  • Altered thyroid function;
  • Neuromuscular diseases;
  • Delirium tremens (psychotic form which generally derives from the chronic abuse of alcohol);
  • Burns;
  • Infectious diseases.

Any type of muscle damage, including injections, can temporarily increase CK.

CK-MB High

  • Acute myocardial infarction;
  • Physical injury of the heart muscle;
  • Myocarditis;
  • Electrocution (electric shock);
  • Defibrillation;
  • Surgery.

Following heart damage, there is an increase in values ​​after about three hours, but the peak - as in the case of Troponin - will not occur before 18 hours. Unlike the latter, however, after a maximum of three days it is possible that no trace remains in the blood.

CK-MM High

  • Inflammation of skeletal muscle (myositis);
  • Muscle injuries;
  • Excess of intramuscular injections;
  • Taking medicines (for example: statins used to reduce cholesterol);
  • Muscular dystrophy;
  • Surgery;
  • Intense physical exercise, especially when it is hot and humid, and the subject is dehydrated;
  • Congenital myopathies;
  • Rhabdomyolysis (muscle tissue rupture secondary to thrombosis, infection, seizure, squeezing and compression of the muscle, trauma, burn, electric shock, etc.).

CK-BB High

  • Brain injuries;
  • Stroke and reduced blood supply to the brain;
  • Pulmonary infarction;
  • Brain tumor;
  • Meningitis;
  • Hypothermia.

Low Creatine Kinase - Causes

The most common causes of low CK values ​​are:

  • Addison's disease;
  • Poor muscle mass;
  • Liver problems.

However, low levels of CK may occur even during pregnancy.

How to measure it

Creatine kinase is measured on a blood sample taken from a vein in the arm.

Preparation

The patient can undergo blood sampling preferably after an 8 to 10-hour fast.

Interpretation of Results

CK Alto

An exponential increase in creatine kinase generally indicates that there has been recent muscle or cardiac damage.

  • Chest pain and increased CK concentrations indicate the likelihood of a recent heart attack. Values ​​that decrease and then increase again may indicate the arrival of a second heart attack or damage to the heart. Normal CK concentrations indicate that there was no muscle damage or that several days were passed before taking the test.
  • Moderately increased concentrations have been observed following intense exercise, such as weight lifting, combat sports or long exercise sessions.
  • Excessive presence of CK in the blood can occur in muscular atrophies also of neurological origin (for example in ALS, amyotrophic lateral sclerosis).

CK Low

A low concentration of CK can be observed in the first months of pregnancy.