Troponin Test

Troponin test is a significant diagnostic marker in the identification of cardiac impairments such as infarctions. It is recommended in almost all medical facilities especially as an advanced cardiac life support diagnostic test. The efficiency of this test is that it helps in identifying small degrees of damage to heart muscle cells. The most common cause of cardiac injury is myocardial ischemia.

For this test to be reliable, it must be administered within 6 to 12 hours of chest pain or any other typical symptom of heart disease. With a Troponin test, patients displaying ECG variations or palpitations can rule out myocardial infarction. Based upon the analysis of the vital signs and Troponin test, the physician recommends a specific type of treatment or procedure associated with the condition.

Troponins are muscle proteins found in striated muscles and their role in identifying cardiac conditions and embolisms associated with brain and lungs are remarkable. These indicators or markers are precise in their identification pattern, which paves the way to rule out complex conditions associated with the heart, lungs and the brain.

There are 2 types of myofilament, a thick filament of myosin and a thin filament of 3 different proteins:

• Actin
  
• Tropomyosin
  
• Troponin
  

Troponin is itself a complex of 3 proteins:
Troponin T
Troponin I
Troponin C.

Troponin T is associated with tropomyosin binding sites, Troponin I inhibits the contraction of actin and myosin - actomyosin ATPase and Troponin C is associated with calcium channel binding. In the cytosol, Troponin T is found in free as well as protein bound forms. The unbound free pool of troponin T is released in the initial phase of myocardial damage while the bound Troponin T is released at a later stage, in tune with the degradation of myofibrils and irreversible myocardial damage.

Acute Myocardial Infarction (AMI) or Myocardial Ischemia is the primary cause of cardiac injury. Troponins - the marker proteins have a unique diagnostic window in that the timeline during which the marker rises, peaks and returns to normal is of significance. Troponin levels rise within 2 - 4 hours after the onset of myocardial necrosis and stays high for up to 14 days. This long window of elevated levels allows detection of Myocardial Infarction that occurred several days ago. Troponin levels enable us to predict the extent of heart muscle damage. Troponin levels in a healthy individual will be negligible (less than 0.5 ng/mL). The greater the amount of troponin in the blood, greater is the damage to the heart. Troponin I value less than 10 microgram per liter is considered as normal whereas troponin T value should be less than 0.1 microgram per liter.

Troponin levels greater than 2.0 ng/mL indicate significant myocardial damage and is at an elevated level of risk for further serious heart conditions. Levels between 0.5 and 2.0 ng/mL indicate a possible diagnosis of unstable angina, other heart ailments or chronic kidney failure. In some cases the finding of unstable angina and an elevated troponin T may well be a unique response to treatment techniques involving anti platelet agents and heparin.

Each of these muscle proteins has specific origin of action and hence they are closely associated with the cardiovascular system. Troponin test is ordered mostly as an emergency care measure in order to stop an adverse effect caused due to angina and Congestive heart failure (CHF).

There are two types of tests for troponins T and I:

1. Traditional quantitative test: Shows an actual measurement of troponin. Usually this test takes about 45 -90 minutes and is useful to distinguish between Myocardial Infarction and unstable Angina.
2. Qualitative test: Shows the result Positive or Negative. This test takes about 15 minutes and is useful in emergency rooms where critical decisions have to be taken based on the presence of Troponin level.
A 'negative' troponin test means that the protein was not detected in the blood. A positive indicates the need for further evaluation.

CK blood test

A Creatinine Kinase test is a blood test that measures the levels of Creatinine phosphokinase (CPK). It is an enzyme found predominantly in the heart tissue, brain and skeletal muscle. The CK blood test is commonly used to diagnose the existence of heart muscle damage. The CK blood test result shows an increase above normal in a person's blood test about six hours after the start of a heart attack.

It reaches its peak in about 18 hours and returns to normal in 24 to 36 hours. When the total CPK level is substantially elevated, then it is indicative of injury or stress to heart, brain or skeletal areas. The small amount of CPK that is normally in the blood comes from the muscles. The CPK blood test also helps in cost-effective management of people with suspected coronary atherosclerosis. It also evaluates the extent of muscle damage caused by drugs, trauma or immobility.

Abnormal CK-MB (one of three CK isoenzymes) or troponin levels are associated with Myocyte Necrosis and the diagnosis of Myocardial infarction. The Cardiac Markers of Cardiac Myocyte Necrosis (damage to the Cardiac muscle cells), myoglobin, CK, CK-MB and troponin I and T are primarily used to identify acute Myocardial Infarction.

It is used in early detection of dermatomyositis and polymyositis. It is also used to distinguish malignant hyperthermia from a post operative infection. It helps to discover carriers of muscular dystrophy.

The normal range for Creatinine Kinase (CK or CPK) blood test:
Male: 38 - 174 units/L
Female: 96 - 140 units/L

Increased levels of CK also can be found in viral myositis and hypothyroidism. Higher than normal CPK levels is indicative of the following conditions:

• Heart attack
  
• Myocarditis
  
• Convulsions
  
• Delirium Tremens
  
• Electric shock
  
• Muscular dystrophy
  
• Pulmonary infarction
  

CK MB

Serum CKMB levels are tested to check for myocardial injury. It is another important cardiac marker. The primary source of CKMB is myocardium although it is also found in skeletal muscle. Typically CKMB tests have now been replaced by Troponin test. But in cases of abnormal Troponin assay results or suspected re-infarction in the hospital, the CKMB serum test is still used.

High levels of CK MB are noticed in cases of polymyositis and rhabdomyolysis. Patients suffering pulmonary embolism, hypothyroidism, and muscular dystrophy or carbon monoxide poisoning can also show higher levels of serum CKMB. The reference range is about 56.2 pg/mL.

Myoglobin

Myoglobin is one of the most important proteins in the human body. It is found in smooth and skeletal muscle tissue; where it binds oxygen and provides energy to power muscular contractions. It is an iron-oxygen binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. Myoglobin is found in skeletal and cardiac muscles. It is a Hemeprotein that facilitates intracellular oxygen storage and transcellular diffusion of oxygen. Myoglobin's affinity for oxygen is higher than hemoglobin. And unlike hemoglobin which is found in the red blood cells, Myoglobin is found in muscle tissues. Myoglobin, together with the cytochromes, is responsible for the red-brown color of muscles.

In 1958, scientists Max Perutz and John Kendrew determined the 3D structure of Myoglobin by X-ray crystallography and interestingly, Myoglobin is the first protein to have its three-dimensional structure determined. In 1962, both these eminent scientists shared the Nobel prize for constructing a three-dimensional model of crystalline sperm-whale Myoglobin utilizing the technique of X-ray diffraction.

Myoglobin structure and functions

• Myoglobin transports or stores oxygen in muscles. Unlike other proteins, myoglobin is able to bind with oxygen because it contains Heme,a metal-containing prosthetic group that allows it to bind to oxygen.
  
  
• Myoglobin consists of a single polypeptide chain
  
  
• Myoglobin occurs as a monomeric heme protein
  
  
• Myoglobin contains only one heme binding sub-unit surrounded by a globular protein, containing eight alpha-helical and six non helical segments, made up of 153 amino acids.
  
  
• During the period of oxygen deprivation, oxymyoglobin releases its bound oxygen for metabolic purposes.
  

Myoglobin test results

For Men: 10 - 95 ng/ml (onset: 1-3 hrs, peak: 6-10 hrs, return to normal: 12-24 hrs)

For Women: 10 - 65 ng/ml (onset: 1-3 hrs, peak: 6-10 hrs, return to normal: 12-24 hrs)

Myoglobin Test

Myoglobin serum test may be used detect muscle damage. Myoglobin is rapidly released after muscle damage, and thus can be a useful bio marker in the early phases of muscle injury. When heart or skeletal muscle is injured, Myoglobin is released into the blood. When the damage is severe, Myoglobin levels in the blood shoot up within few hours of damage.

Excess Myoglobin in the blood is filtered by kidneys and released into the urine. And thus, severe muscle damage followed by high amounts of Myoglobin in the serum and eventually in the urine may lead to renal failure. Myoglobin levels are tested to identify the presence and timing of muscle damage. However, it cannot determine the location of muscle injury/damage. The Myoglobin blood test is also commonly used to identify a recent heart attack or acute myocardial infarction. Other sensitive markers like troponin are more commonly used today to detect heart conditions.