I NTRODUCTION TO LABORATORY MEDICINE

L IPID CHEMISTRY AND CARDIOVASCULAR PROFILE Main lipids in the blood are the triglycerides and cholesterol. These are insoluble in the water. Transport in the blood is via lipoproteins. 4 major classes of lipoproteins. Chylomicrons Very low density lipoproteins (VLDL) Low density lipoproteins (LDL) High density lipoproteins (HDL)

L IPOPROTEINS COMPOSITIONS

C OMPOSITION OF LIPOPROTEINS Class Diamete r (nm) % protein % cholesterol % phospholipi d % triacylglyc erol & cholesterol ester HDL 5– LDL 18– IDL 25– VLDL 30– Chylomicr ons <28784

LIPOPROTEINS Chylomicrons carry triglycerides (fat) from the intestines to the liver, to skeletal muscle, and to adipose tissue. Very-low-density lipoproteins (VLDL) carry (newly synthesised) triglycerides from the liver to adipose tissue. Intermediate-density lipoproteins (IDL) are intermediate between VLDL and LDL. They are not usually detectable in the blood. Low-density lipoproteins (LDL) carry cholesterol from the liver to cells of the body. LDLs are sometimes referred to as the "bad cholesterol" lipoprotein. High-density lipoproteins (HDL) collect cholesterol from the body's tissues, and take it back to the liver. HDLs are sometimes referred to as the "good cholesterol" lipoprotein.

C HYLOMICRON STRUCTURE

L IPOPROTEIN METABOLISM

CARDIAC PROFILE TEST ENZYMES Creatinine Kinase –MB(CK-MB) Lactate Dehydrogenase(LDH 1 and 2) Aspartate Aminotransferase(AST)/Serum Glutamate Oxaloacetate Transaminase(SGOT) Alanine Aminotransferase(ALT)/ Serum Pyruvate Transaminase(SGPT) LIPID PROFILE CHOLESTEROL TRIGLYCERIDE HDL LDL

C ARDIAC PROFILE Cardiac Enzymes Cardiac Profile assesses the function of the heart’s muscle and the increased level of enzymes following a myocardial infarction. The cardiac enzymes include the following:  Aspartate aminotransferase (AST)  Lactate dehydrogenase (LD)  Creatine Kinase (CK)

ASPARTATE AMINOTRANSFERASE (AST) (SGOT) found in all tissue, especially the heart, liver, and skeletal muscles it catalyzes the transfer of the amino group of aspartic acid to alpha- ketoglutaric acid to form oxaloacetic acid and glutamic acid Reaction catalyzed: Amino group Alpha-keto group Oxaloacetate & In aspartic acid in alpha-ketoglutaric acid Glutamate Reference range: < 35 U/L in male and < 31 in female Considerations in AST assays -Serum is the best specimen -Hemolyzed samples must be avoided -Muscle trauma like intramuscular injections, exercise, or surgical operation can significantly increase AST levels

C LINICAL SIGNIFICANCE  Myocardial infarction  In myocardial infarction, AST levels are usually 4-10 times the upper limit of normal  These develop within 4-6 hours after the onset of pain  Peak on the 24 th – 36 th hour  Usually normalize on the 4 th or 5 th day  Muscular dystrophy  Hepatocellular disorders  Skeletal muscle disorders  Acute pancreatitis

I NCREASED LEVELS OF AST Chronic alcohol abuse Drug hepatoxicity Pulmonary infarction Pericarditis Acute hepatitis Skeletal muscle disorders

D ECREASED LEVELS OF AST Pregnant women Falsely elevated results Bilirubin Aceto-acetatae N-acetyl compounds P-aminophenol Sulfathiozole Isoniazid Methyldopa L-dopa Ascorbic acid Interferences Mercury Cyanide fluoride

LACTATE DEHYDROGENASE (LDH) Catalyzes the reversible oxidation of lactate to pyruvate Used to indicate AMI Is a cytoplasmic enzyme found in most cells of the body, including the heart Not specific for the diagnosis of cardiac disease

D ISTRIBUTION OF LD ISOENZYMES LD1 and LD2 (HHHH, HHHM) Fast moving fractions and are heat-stable Found mostly in the myocardium and erythrocytes Also found in the renal cortex LD3 (HHMM) Found in a number of tissues, predominantly in the white blood cells and brain LD4 and LD5 (HMMM, MMMM) Slow moving and are heat labile Found mostly in the liver and skeletal muscle

C ONSIDERATIONS IN LD ASSAYS Red cells contain 150 times more LDH than serum, therefore hemolysis must be avoided LDH has its poorest stability at 0°C Clinical Significance In myocardial infarction, LD increases 3-12 hours after the onset of pain Peaks at hours and remain elevated for days In MI, LD1 is higher than LD2, thus called “flipped” LD pattern

FLIPPED LDH An inversion of the ratio of LD isoenzymes LD 1 and LD 2 ; LD 1 is a tetramer of 4 H–heart subunits, and is the predominant cardiac LD isoenzyme; Normally the LD 1 peak is less than that of the LD 2, a ratio that is inverted–flipped in 80% of MIs within the first 48 hrs DiffDx. LD flips also occur in renal infarcts, hemolysis, hypothyroidism, and gastric CA

I NCREASED LEVELS OF LD Trauma Megaloblastic anemia Pulmonary infarction Granulocyte leukemia Hodgekin’s disease Hemolytic anemia Infectious mononucleosis Progressive muscular dystrophy (PMD)

CREATINE KINASE (CK) Is a cytosolic enzyme involved in the transfer of energy in muscle metabolism Catalyzes the reversible phosphorylation of creatine by ATP -Is a dimer comprised of two subunits, resulting in three CK isoenzymes The B, or brain form The M, or muscle form

Three isoenzymes isolated after electrophoresis : CK-BB (CK1) isoenzyme Is of brain origin and only found in the blood if the blood- brain barrier has been breached CK-MM (CK3) isoenzyme Accounts for most of the CK activity in skeletal muscle CK-MB (CK2) isoenzyme Has the most specificity for cardiac muscle It accounts for only 3-20% of total CK activity in the heart Is a valuable tool for the diagnosis of AMI because of its relatively high specificity for cardiac injury Established as the benchmark and gold standard for other cardiac markers

Considerations in CK assays CK is light sensitive and anticoagulants like oxalates and fluorides inhibit its action CK in serum is very unstable and rapidly loss during storage Exercise and intramuscular injections causes CK elevations

Clinical Significance -In myocardial infarction, CK will rise 4-6 hours after the onset of pain -Peaks at hours and returns to normal on the third day -CK is the most specific indicator for myocardial infarction (MI)

Raised levels of CK Progressive muscular dystrophy Polymyositis Acute psychosis Alcoholic myopathy Hypothyroidism Malignant hyperthermia Acute cerebrovascular disease Trichinosis and dermatomyositis Normal Value: a. Male – IU/mL b. Female – IU/mL

CHOLESTEROL Normal values: range varies according to age Total Cholesterol: mg% Cholesterol esters: 60-75% of the total cholesterol

C HOLESTEROL IS ADVISED IF YOU  have been diagnosed with coronary heart disease, stroke or mini-stroke (TIA) or peripheral arterial disease (PAD)  are over 40  have a family history of early cardiovascular disease  have a close family member with cholesterol-related condition  are overweight  have high blood pressure, diabetes or a health condition that can increase cholesterol levels, such as an underactive thyroid

F ACTORS LEADING TO RAISED CHOLESTEROL an unhealthy diet: some foods already contain cholesterol (known as dietary cholesterol) but it is the amount of saturated fat in your diet which is more importantsaturated fat smokingsmoking: a chemical found in cigarettes called acrolein stops HDL from transporting cholesterol to the liver, leading to narrowing of the arteries (atherosclerosis) having diabetes or high blood pressure(hypertension)diabeteshigh blood pressure having a family history of stroke or heart disease There is also an inherited condition known as familial hypercholesterolaemia (FH). This can cause high cholesterol even in someone who eats healthy diet.

T RIGLYCERIDES Ester derived from glycerol and three fatty acids. Main lipids in the blood and important energy substrate. Insoluble in water. Hypertriglyceridemia Not an important risk facotr for coronary artery disease. It can cause pancreatitis when severe. Both hypertriglyceridemia and hypercholesterolemia are associated with various types of cutaneous fat deposition and xanthomatas. Hypertension Very common clinical problem. Usually essential type meaning that have no identifiable cause. Investigations for treatable causes like endocrine is necessary.

S PECIAL CHEMISTRY Definition Special Chemistry is a subsection of the Chemistry Laboratory of the Division of Clinical Pathology. This includes the tests which are not the part of the routine panel.  Electrophoresis  Urine chemistry  Radioimmunoassay.

Test Sensitivity and specificity Troponin test The most sensitive and specific test for myocardial damage. Because it has increased specificity compared with CK-MB, troponin is a superior marker for myocardial injury. Myoglobin (Mb) low specificity for myocardial infarction. Rises very early within 1-3 hours of pain. Pro-brain natriuretic peptide (pro-BNP) This is increased in patients with heart failure. It has been approved as a marker for acute congestive heart failure Glycogen phosphorylase isoenzyme BB high sensitivity and specificity early after chest pain. by ELISA Normal troponin levels 12 hours after chest pain has started mean a heart attack is unlikely

Myloperoxidase (MPO)  Elevated in chronic conditions CRP  Marker of atherosclerosis Pregnancy associated plasma protein A (PAPPA)  elevated in atherosclerosis when atheroma is about to rupture Oxidized LDL  A marker of atherosclerosis Choline  Test of prognosis  Rises in chest discomfort even without rise in troponin level.