Enzyme Markers

CPK isoenzymes

The CPK isoenzymes test measures the creatine phosphokinase (CPK) in the blood. CPK enzymes are in the heart, brain, and skeletal muscles. Normal CPK levels vary by age, gender, and race.

Each laboratory may have minor differences in reference ranges, as well. In general, a CPK level of approximately 200 units per liter (U/L) or less is considered normal in an adult. This is the total CPK level in your body. More specific testing can be done, but this is not routine.

Read more: CPK isoenzymes test »

CPK-1 resides mostly in the brain and lungs. Increased levels of CPK-1 can be due to:

• brain cancer
• brain injury, stroke, or bleeding in the brain
• pulmonary infarction, which is the death of lung tissue
• seizure
• electroconvulsive therapy

CPK-2 levels rise following a heart attack. Increased levels of CPK-2 may also be due to:

• open heart surgery
• inflammation of the heart muscle
• heart injury
• defibrillation
• electrical injuries
• chest compressions after cardiac arrest

High CPK-3 levels can be a sign of muscle stress, a crush injury, or injury due to:

• muscle damage, dystrophy, or inflammation
• intramuscular injections
• electromyography, which is a muscle and nerve function test
• recent surgery
• seizures
• strenuous exercise

Heart enzymes

Some heart enzymes slowly enter your blood if you’ve had a heart attack and your heart is damaged as a result. A general test for emergency room patients with heart attack symptoms is a test for the presence of certain proteins in your blood. A doctor may check CPK-2, also known as CK-MB. This marker is highly specific for heart muscle injury and rises rapidly during a heart attack. Normal CK-MB should be between 5-25 international units per liter (UI/L).

The preferred marker of heart injury, though, is a protein called troponin. Troponin should generally be less than 0.02 nanograms per milliliter (ng/mL). The level takes longer to rise than CK-MB, but the protein stays in the bloodstream longer.

Learn more: Symptoms of a heart attack »

Liver enzymes

Elevated liver enzymes may be due to inflammation or damaged liver cells. Usually, elevated liver enzymes are related to an acute injury, or a process that occurred over a short period of time due to:

• prescription medications, such as statins
• over-the-counter (OTC) medications, such as acetaminophen (Tylenol)
• alcohol consumption
• heart failure or heart attack
• liver disease, such as hepatitis, fatty liver disease, cancer, and cirrhosis
• obesity
• celiac disease, which is a digestive condition
• viruses, such as cytomegalovirus infection; hepatitis A, B, C, E viruses; mononucleosis; and Epstein-Barr virus
• inflammatory diseases, such as dermatomyositis, pancreatitis, and gallbladder inflammation
• muscular diseases, such as muscular dystrophy or polymyositis
• ischemia, or lack of oxygen going to the liver, such as during cardiac arrest
• hemochromatosis, which is a disorder in which there’s too much iron in the blood
• underactive thyroid
• Wilson disease, which is a disorder where there’s too much copper stored in the body
• physical trauma to the organ

There are several markers that can be used to test liver function. These markers help separate whether or not the injury is to the liver parenchyma (liver cells) or to the biliary system. For the purposes of this article, the important tests are the liver aminotransferases: alanine aminotransferase (ALT) and aspartate aminotransferase (AST).

ALT is primarily produced by the liver, while AST can be from the liver, cardiac muscle, skeletal muscle, kidney, and brain. A normal ALT level is 29-33 IU/L for men, and 19-25 IU/L for women. A normal AST level may range from 10-40 IU/L for men and 9-32 IU/L for women.

These reference ranges vary from hospital to hospital. It’s important to compare your liver enzyme levels to the reference ranges provided by the lab.

The test is a routine blood test that takes place in a laboratory. No fasting or special preparation is necessary. But tell your doctor before the test about all prescription and OTC medications and supplements you take.

A blood test involves the following steps:

• A healthcare provider will use an antiseptic to clean a small area of your arm, usually the inside of your elbow or the back of your hand.
• They’ll then wrap an elastic band around your upper arm to create pressure and make it easier to access a vein.
• They’ll insert a needle into your vein and blood will flow into a small vial. You’ll likely feel the stick of the needle or a stinging sensation.
• After filling the vial, the healthcare provider will remove the elastic band and the needle.
• They’ll place a bandage over the puncture site and send the blood sample to a lab for analysis.
• The procedure should take only a few minutes.

Your arm may be sore at the puncture site, and you might have some mild bruising or brief throbbing.

Most people have no serious or lasting side effects from a blood test. Rare complications include:

• bleeding
• lightheadedness
• fainting
• infection, which is a small risk whenever the skin is broken

Contact your doctor immediately if you have any of these symptoms.

Abnormal test results can indicate a variety of problems from disease to a simple muscle strain because enzymes are present in every cell of your body. Your doctor will be able to determine a proper course of treatment based on your exact enzyme marker levels and the symptoms you’re having.