Heart health is becoming a matter of concern nowadays, even for young people. The rising cases of cardiac arrest make it highly crucial for everyone to assess their heart health and diagnose potential heart problems. The CPK test is an important laboratory test that helps physicians assess whether there is any damage to cardiac muscles or skeletal muscles in symptomatic patients.

This article summarises key information you should know about the Creatine Phosphokinase test.

What is the CPK Test?

The CPK blood test refers to a simple blood test that measures the level of creatine phosphokinase enzymes. When your heart or muscle tissues get damaged, CPK comes out from the cells into the blood. This can happen for various reasons, including:

• Stress
• Injury
• Lack of Oxygen 
• Underlying Disease

Using the CPK Test, doctors can determine the extent of damage done to the body's organs and muscles.

Purpose of CPK Test

The CPK blood test serves several important diagnostic purposes:

• It allows early detection of heart attacks by signalling damage to cardiac tissue through elevated CPK levels. It helps distinguish heart attacks from other causes of chest pain.
• It helps diagnose muscle diseases like muscular dystrophy, dermatomyositis and polymyositis, which cause inflamed and damaged muscles.
• It allows evaluation of the cause of unexplained symptoms like chronic muscle soreness and weakness based on whether muscle injury is detected.
• It enables monitoring the progress of healing and efficacy of treatment after surgeries, injuries or conditions affecting heart and skeletal muscles by tracking changes in CPK levels.

When is a CPK Test Needed?

Some common indications for performing a CPK isoenzymes blood test include

• If a patient has symptoms of a heart attack like acute severe chest pain along with sweating, nausea, etc. It allows rapid diagnosis of myocardial infarction.
• To investigate the cause behind nonspecific symptoms like unexplained muscle pain and weakness.
• If an individual has a family history of inheritable muscular disorders like muscular dystrophy, a baseline CPK level test allows early detection in future.
• To know baseline CPK levels if a patient is prescribed treatment with drugs like statins and steroids that are known to cause muscle damage in some people.
• To monitor healing and treatment response for diagnosed heart conditions or muscle diseases by comparing before and after medication CPK levels.

Uses of CPK Test

Some uses of the CPK blood test include:

• It allows prompt diagnosis of myocardial infarction by detecting heart muscle damage through elevated cardiac CPK enzymes.
• It helps differentiate angina and other causes of acute chest pain from actual heart attacks.
• Enables diagnosis of inherited and acquired muscle disorders like muscular dystrophy and dermatomyositis, causing muscle inflammation by indicating skeletal muscle injury.
• Establish baseline CPK levels before starting treatment with cholesterol drugs and anabolic steroids that can potentially damage muscles.
• Monitor the effectiveness of treatment for muscle-weakening diseases.
• Evaluate recovery after bypass heart operations, stab wounds, and crush traumas that cause muscle injury.

How to Prepare for the CPK Test

To prepare for a CPK blood test, patients should:

• Disclose current medications as certain drugs affect results.
• Avoid exercising extensively a day before the test as it may cause temporary CPK elevation.
• Refrain from drinking alcohol for 24 hours prior to the test as it impacts CPK levels temporarily.
• Report any recent incidents that may cause muscle injury, like trauma from accidents or IM injections that can raise CPK levels.
• No prior appointments, fasting or changes in diet are required for the routine CPK blood analysis.

What Happens During the CPK Test?

The CPK test is a routine blood test that requires very little preparation and is completed quickly:

• The healthcare provider will first clean the area with an antiseptic solution, usually the crook of the elbow or back of the palm, where veins are easily accessible. This reduces the risk of infection.
• A tight band may be wrapped around the upper arm as a tourniquet, which causes the veins to bulge with blood and become more prominent. This aids in quicker vein access.
• Using a sterile needle, around 2-5 mL of blood is drawn and collected into a sample bottle. A slight stinging sensation may be felt during needle insertion.
• After sufficient blood is collected, the needle is removed immediately, and the puncture site is pressed to stop bleeding and is covered with a bandage.
• The blood sample is sent to the laboratory for assessment of CPK levels.
• At the diagnostic laboratory, CPK variants CPK1, CPK2 and CPK3 are separated and measured using a technique called electrophoresis to generate test reports.

What Do CPK Test Results Mean?

• CPK Normal Range:
  • The CPK Normal Value is between 10 to 120 units per litre of blood.
• CPK Low Levels:
  • Levels lower than 10 U/L indicate abnormally low total CPK levels.
  • Seen in nutritional deficiencies and liver disorders.
  • It may suggest weakened heart muscle or skeletal muscles due to advanced injuries.
• CPK High Levels:
  • Levels exceeding 200 U/L are considered CPK blood test high levels.
  • Signals damage to the brain, heart, lungs or skeletal muscle tissues.
  • Help determine affected organs based on which CPK subtype (CPK1, CPK2 or CPK3) is specifically elevated.

What Abnormal Results Mean

• Elevated CPK1 levels may indicate - stroke, brain injury, bleeding, pulmonary infarction
• High CPK2 levels may signify - myocardial infarction, myocarditis or heart attack
• Increased CPK3 levels can mean - muscular dystrophy, trauma from accidents, statues, burns, etc.

Conclusion

The CPK test serves as an important diagnostic tool in modern medical practice to objectively detect early tissue damage, which helps guide prompt treatment to minimise permanent injury in time-sensitive cases like myocardial infarction. It provides confirmatory evidence of muscular diseases and is an inexpensive and risk-free check-up that aids clinical decision-making for musculoskeletal issues.

FAQs

1. What is a normal level of CPK or CK test?

The normal CPK reference range is between 10-120 U/L in the blood. Values in this range are considered normal.

2. What happens if the CPK test is positive?

A positive test means CPK levels in the blood are higher than the set normal upper limit of 120 U/L. Abnormally elevated results signify damage or injury to the brain, heart, lungs or skeletal muscle tissues.

3. What happens if the CPK test is negative?

A negative or normal CPK test result indicates levels within the expected 10-120 U/L range. It rules out acute, extensive injury to the heart or skeletal muscle when symptoms may otherwise be ambiguous, like unexplained body aches. 

4. What parameters are measured in the CPK test?

The CPK blood analysis specifically measures levels of CPK variants CPK1, CPK2 and CPK3 using a lab technique called electrophoresis. The CPK1 subtype is abundant in brain and lung tissue and CPK2 in heart muscles, while CPK3 predominates in skeletal muscles and blood plasma.

5. How long does the CPK test take to perform?

The actual blood sample collection procedure takes only a few minutes. Sample transportation, laboratory analysis using electrophoresis and generation of the report with results interpretation may take anywhere between a few hours to 1 to 2 days, depending on the diagnostic facility.

6. Are there any risks to the test?

The CPK test poses negligible risks since it only involves a routine blood draw. Still, slight discomfort, bruising or rarely infection localised to puncture sites or dizziness from needles may occur. It is non-invasive and considered very safe, with no preparation or restrictions needed.