Cardiac Markers: CK-MB and Troponin

Cardiac markers are tests that indicate damage to the heart that become detectable in the blood. There are 2 such markers CK-MB and troponin.

CK/Creatine Kinase

What is CK or creatine kinase? CK is an enzyme found in all muscle and brain. Then how does this cardiac marker differentiate from the heart or cardiac muscle. There are 3 types of CK enzymes one found in skeletal muscle (CK-MM), heart muscle (CK-MB) and brain (CK-BB). CK-M is a muscle type of the enzyme and CK-B is the brain type. The problem with the CK test is that it isn’t as neat and tidy as suggested there elements of each category of CK enzyme found in the skeletal muscle and heart. Which can be broken down as follows CK-BB is 100% found in the brain (great test to find brain damage by the way), CK-MM is found 99% in skeletal muscle and 80% in heart muscle (Not good a good cardiac marker at all and weird the percentages don’t add up) and CK-MB is found 20% in the heart muscle and 1% in the skeletal muscle. A word about percentages, the heart has 80% CK-MM and 20% CK-MB. Looking at it this way the percentages do add up! Wait why not test for CK-MM and don’t bother about the CK-MB. Look at how much CK-MM there is in skeletal muscle (99%). By focusing on this cardiac marker you are actually commented on how much skeletal damage there is and not heart muscle damage and it is the heart we want to look at. Even-though there is less CK-MB in the heart, the overall ratio of heart to skeletal muscle is better (20% heart to 1% skeletal). It is in this ratio the test is valid, but it is not perfect. It is this reason that this test alone does not mean that the elevation is solely caused by heart damage since that it is still found in 1% of skeletal muscle, but it does qualify the test as valid. In combination with other tests does it show its true power.

Troponin

The discovery of troponin has elevated cardiac testing to new heights. Troponin’s power has proven itself over and over again. Unlike CK-MB, troponin is solely found in the heart and any evidence found of it in the blood indicates damage to the heart. It is a 99% accurate cardiac marker (I hesitate to say 100% since there are no guarantees in medicine, but it is close). When investigating heart damage it is imperative to ascertain a timeline. Troponin is time dependant by starting to be noticeable in the blood 6 to 8 hours after damage has occurred and remaining in the blood 7 to 10 days after. So if a doctor is concerned about heart damage or heart attack and the pain started 3 hours prior then the lack of troponin in the blood does not mean no attack has occurred it means that testing for the cardiac marker was done too early. A second blood test would need to be done in 3 to 5 hours to look for the presence of the enzyme. If this test is negative (no troponin detected) then no heart damage has occurred. If it is positive then the higher the number indicates the severity of the damage. It doesn’t mean that you wait to go the hospital, on the contrary, still get to the hospital as fast you can. Medicine works best with multiple tests, such as an ECG/EKG which will rule a heart attack right away. If the ECG test is positive then treatment can be done immediately resulting in no heart damage at all. Troponin is then important if the ECG/EKG is negative. A positive result means heart damage has occurred, but from what? Congested heart failure? Asthma exacerbation (worsening of)? Or silent MI? there are multiple reasons why a troponin would be high and a qualified physician can only make that determination based on a thorough cardiac examination.

If they are found in the cell then how do they become visible in the blood? Good question! Normally enzymes aren’t found in the blood at all which makes them good cardiac markers. The cells hold onto the enzymes and if they aren’t detected in the blood we call that a “negative test” or “results are negative”. When the muscle or brain is damaged some how it causes a series of events that causes necrosis or cell death. The event that starts the process is a physical injury such as a fall or car accident that physically hurts the muscle. It could also be from lack of blood flow that doesn’t allow food to get to the cell. These 2 actions start an immune response. You would know the immune response from getting a cold or flu or hay fever or even an allergic reaction. What happens is there is an increase in blood flow to a localized area; which in turn causes swelling. The point to these reactions is to bring the white blood cells to an area to literally eat away the damaged tissue. Since the cell is now being broken further it “spills” the enzymes into the blood stream to be detected by our blood tests.

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