CARDIAC ENZYME AND EXPLORATION
- CPK: - normal values: - men: less than 174 Units/liter - women: less than 140 Units/liter -
and BB (brain) normally comprise 0%;
- abnormal values: -
myocardial infarct -
CPK levels begin to rise 4-6 hours after MI has started and reaches its peack values within 30 hrs; - look for an elevation of the CPK MB isoenzymes at 4-6 hours (in MI the CPK MB is more than 5% of total CPK);
- post surgical elevation: there will be an elevation of the CPK level, but the CPK MB percentage should be close to 0; - polymyositis -
Troponin I and T:
- these are cardiac
specific muscle proteins which are elevated with cardiac
muscle damage; -
Test Includes Triglycerides, cholesterol, HDL cholesterol, LDL cholesterol, HDL/cholesterol ratio
Volume 7 mL
Collection Routine venipuncture
Patient Preparation A 12- to 14-hour fast is required. The patient should be on his/her normal diet for several days prior to having the blood drawn.
-Desirable: <200 mg/dL
-Borderline-high: 200-239 md/dL
-High: = 240 mg/dL
-Low (major risk factor): <35 mg/dL
-High (negative risk factor): : = 60 mg/dL
For secondary prevention in adults with evidence of coronary heart disease, the optimum LDL cholesterol level is <100 mg/dL.
-Desirable: <130 mg/dL
-Borderline-high: 130-159 mg/dL
-High: : = 160 mg/dL
-Normal <200 mg/dL
-Borderline-high: 200-400 mg/dL
-High: 400-1000 mg/dL
-Very high: > 1000 mg/dL
Creatine Kinase - Total:
The total CK is a simple and inexpensive test that is readily available using many laboratory instruments. However, an elevation in total CK is not specific for myocardial injury, because most CK is located in skeletal muscle, and elevations are possible from a variety of non-cardiac conditions.
Creatine Kinase - MB Fraction:
Creatine kinase can be further subdivided into three isoenzymes: MM, MB, and BB. The MM fraction is present in both cardiac and skeletal muscle, but the MB fraction is much more specific for cardiac muscle: about 15 to 40% of CK in cardiac muscle is MB, while less than 2% in skeletal muscle is MB. The BB fraction (found in brain, bowel, and bladder) is not routinely measured.
Thus, CK-MB is a very good marker for acute myocardial injury, because of its excellent specificity, and it rises in serum within 2 to 8 hours of onset of acute myocardial infarction. Serial measurements every 2 to 4 hours for a period of 9 to 12 hours after the patient is first seen will provide a pattern to determine whether the CK-MB is rising, indicative of myocardial injury. The CK-MB is also useful for diagnosis of reinfarction or extensive of an MI because it begins to fall after a day, dissipating in 1 to 3 days, so subsequent elevations are indicative of another event.
A "cardiac index" can provide a useful indicator for early MI. This is calculated as a ratio of total CK to CK-MB, and is a sensitive indicator of myocardial injury when the CK-MB is elevated.
The CK-MB fraction exists in two isoforms called 1 and 2 identified by electrophoretic methodology. The ratio of isoform 2 to 1 can provide information about myocardial injury.
An isoform ratio of 1.5 or greater is an excellent indicator for early acute myocardial infarction. CK-MB isoform 2 demonstrates elevation even before CK-MB by laboratory testing. However, the disadvantage of this method is that it is skilled labor intensive because electrophoresis is required, and large numbers of samples cannot be run simultaneously nor continuously. False positive results with congestive heart failure and other conditions can occur.
Troponin I and T are structural components of cardiac muscle. They are released into the bloodstream with myocardial injury. They are highly specific for myocardial injury--more so than CK-MB--and help to exclude elevations of CK with skeletal muscle trauma. Troponins will begin to increase following MI within 3 to 12 hours, about the same time frame as CK-MB. However, the rate of rise for early infarction may not be as dramatic as for CK-MB.
Troponins will remain elevated longer than CK--up to 5 to 9 days for troponin I and up to 2 weeks for troponin T. This makes troponins a superior marker for diagnosing myocardial infarction in the recent past--better than lactate dehydrogenase (LDH). However, this continued elevation has the disadvantage of making it more difficult to diagnose reinfarction or extension of infarction in a patient who has already suffered an initial MI. Troponin T lacks some specificity because elevations can appear with skeletal myopathies and with renal failure.
Myoglobin is a protein found in skeletal and cardiac muscle which binds oxygen. It is a very sensitive indicator of muscle injury. The rise in myoglobin can help to determine the size of an infarction. A negative myoglobin can help to rule out myocardial infarction.. It is elevated even before CK-MB. However, it is not specific for cardiac muscle, and can be elevated with any form of injury to skeletal muscle.
The LDH has been supplanted by other tests. It begins to rise in 12 to 24 hours following MI, and peaks in 2 to 3 days, gradually dissipating in 5 to 14 days. Measurement of LDH isoenzymes is necessary for greater specificity for cardiac injury. There are 5 isoenzymes (1 through 5). Ordinarily, isoenzyme 2 is greater than 1, but with myocardial injury, this pattern is "flipped" and 1 is higher than 2. LDH-5 from liver may be increased with centrilobular necrosis from passive congestion with congestive heart failure following ischemic myocardial injury.