Introduction to Clinical Chemistry University of Lusaka – Medical School CONTENTS Objectives Equipment used Tests performed Anatomy of the Heart Preferred Specimen Cardiac enzymes Reference ranges – cardiac enzymes Significant considerations Conclusion OBJECTIVES To know the various types of automated equipment used in the Clinical Chemistry Laboratory To understand the different types of tests that are performed in the Clinical Chemistry Laboratory To identify the different parts of the heart and understand a Heart attack To know the cardiac enzymes and understand their release into the blood circulation following the Heart attack Equipment Used Chemistry analysers Electrolyte analysers Urine Chemistry analysers Glucose analysers Spectrophotometer Pipettes Microscopes etc. Tests Performed Cardiac enzymes Liver function tests Kidney function tests Electrolytes Lipid profile Hormone profile – Thyroid and Fertility tests Random blood sugar (RBS) Fasting blood sugar (FBS) Glucose tolerance test (GTT) etc. THE HEART MYOCARDIAL INFARCTION – HEART ATTACK The Heart requires constant supply of oxygen and nutrients, like any body muscle The Aorta and Coronary arteries deliver oxygenated blood If one of these arteries or branches becomes blocked suddenly, a portion of the heart is starved of oxygen (cardiac ischemia) If cardiac ischemia lasts too long, the starved heart tissue dies i.e. Myocardial Infarction (MI) SYMPTOMS OF MI Pressure or tightness in the chest Pain in the chest, back, jaw and other upper body parts Shortness of breath, sweating, nausea, vomiting, anxiety, dizziness, fainting, cough and a fast heart rate LABORATORY INVESTIGATIONS - PREFERRED SPECIMEN Blood No anticoagulant Clotted Centrifuged Serum used for test Green/Yellow top tubes also used SERUM SEPERATED FROM CLOTTED RBCs CARDIAC ENZYMES (BIOMARKERS) Enzymes – are protein in nature and are produced by the body to speed up specific chemical reactions Cardiac enzyme test – measure of the amount of cardiac enzymes in the blood Cardiac enzymes are normally present in low quantities in the blood circulation CARDIAC ENZYMES Almost undetectable levels However, when elevated, it indicates that the heart muscle may be injured or may not be receiving adequate oxygen for normal functioning When the heart suffers an injury (Heart attack) it releases certain enzymes CARDIAC BIOMARKERS Troponin T (TnT)- the tropomyosinbinding component Troponin I (TnI)-the inhibitory component Troponin C (TnC)- the calciumbinding component(not specific for the heart) Creatine phosphokinase (CPK) Myoglobin Above are more specific to detecting heart injury OTHERS – Non specific Aspartate Transaminase or Aminotransferase (AST) or Serum glutamic – Oxaloacetic (SGOT) Lactic acid Dehydrogenase (LDH) TROPONIN Troponin I and T are normal proteins that are significant in muscle heart contraction They are released into circulation between 3 – 4 hours after MI and remain detectable for 10 days following MI Troponin elevation is much more sensitive than myoglobin and even CPK for MI detection CREATINE PHOSPHOKINASE - CPK Enzyme found in higher concentrations in the heart and skeletal muscles Exists in a very few organs hence CPK used as a specific index of injury to myocardium and muscle CPK is divided into three Isoenzymes: BB (CK-1), MB (CK-2) and MM (CK-3) CREATINE PHOSPHOKINASE - CPK CK-MB primarily found in the heart muscle CK-MM primarily found in the skeletal muscle CK-BB primarily found in the GIT and genitourinary tracts Elevation of MB provides a more definitive indication of myocardial cell damage than total CPK alone CREATINE PHOSPHOKINASE - CPK Increases in circulation approximately 3 – 4 hours after MI and remains elevated for 3 – 4 days This makes it useful for detecting re-infarction in the window of 4 – 10 days after the initial attack Troponin remains elevated for 10 days making it less useful for detecting re-infarction MYOGLOBIN Oxygen – binding protein of striated muscle Resembles haemoglobin but is unable to release oxygen except at extremely low tension Injury to skeletal muscle including MI will result in the release of myoglobin MYOGLOBIN Because skeletal muscle contains myoglobin, this test is quite non – specific for MI detection Myoglobin is detectable within 30 minutes after MI Early marker of injury to muscle tissue Troponin and CPK may take 3 – 4 hours after MI to be detected in the blood CARDIAC ENZYMES - GRAPH CARDIAC ENZYMES – REFERENCE RANGES CPK Also measured in U/L (units per litre) Normal reference range for adults 19 years old and above 38 – 174U/L For children 6 – 18 years old, 35 – 185U/L Cardiac enzymes – significant considerations Patients undergoing a cardiac enzyme test do not need to fast or undergo any special preparations Clinicians often order this test in an emergency situation when they suspect that a patient may be having a heart attack Cardiac enzyme test also helps to assess the level of damage caused by the heart attack The higher the concentrations of these enzymes in circulation, the more damaged the heart is CONCLUSION Various automated equipment are used in the Clinical Chemistry Lab Several tests are performed including Cardiac enzyme tests using serum Cardiac enzymes are usually very low in concentrations in the blood In case of MI, certain enzymes are released into the blood circulation thus increasing their concentrations These enzymes are released at different times and last in the blood for different number of days Cardiac enzymes are evaluated using known normal ranges REFERENCES 1.Laposata M Laboratory Medicine: The Diagnosis of Disease in the Clinical Laboratory (2014). Lange ISBN: 978-0-071-8055-44
