Introduction to laboratory medicine

1. Introduction to laboratory medicine

2. Lipid 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)

3. Lipoproteins compositions

4. Composition of lipoproteins

5. 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.

6. Chylomicron structure

7. Lipoprotein metabolism

8. CARDIAC PROFILE TEST • ENZYMES • CreatinineKinase –MB(CK-MB) • Lactate Dehydrogenase(LDH 1 and 2) • AspartateAminotransferase(AST)/Serum Glutamate OxaloacetateTransaminase(SGOT) • AlanineAminotransferase(ALT)/ Serum PyruvateTransaminase(SGPT) • LIPID PROFILE • CHOLESTEROL • TRIGLYCERIDE • HDL • LDL

9. Cardiac 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: • Aspartateaminotransferase (AST) • Lactate dehydrogenase (LD) • CreatineKinase (CK)

10. 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

11. Clinical 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 24th – 36th hour • Usually normalize on the 4th or 5th day • Muscular dystrophy • Hepatocellular disorders • Skeletal muscle disorders • Acute pancreatitis

12. Increased levels of AST • Chronic alcohol abuse • Drug hepatoxicity • Pulmonary infarction • Pericarditis • Acute hepatitis • Skeletal muscle disorders

13. Decreased 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

14. 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

15. Distribution 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

16. Considerations 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 48-60 hours and remain elevated for 10-14 days • In MI, LD1 is higher than LD2, thus called “flipped” LD pattern

17. flipped LDH An inversion of the ratio of LD isoenzymes LD1 and LD2; LD1 is a tetramer of 4 H–heart subunits, and is the predominant cardiac LD isoenzyme; Normally the LD1 peak is less than that of the LD2, 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

18. Increased levels of LD • Trauma • Megaloblastic anemia • Pulmonary infarction • Granulocyte leukemia • Hodgekin’s disease • Hemolytic anemia • Infectious mononucleosis • Progressive muscular dystrophy (PMD)

19. 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

20. 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

21. 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

22. Clinical Significance • -In myocardial infarction, CK will rise 4-6 hours after the onset of pain • -Peaks at 18-30 hours and returns to normal on the third day • -CK is the most specific indicator for myocardial infarction (MI)

23. 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 – 25-90 IU/mL • b. Female – 10-70 IU/mL

24. CHOLESTEROL • Normal values: range varies according to age • Total Cholesterol: 150-250mg% • Cholesterol esters: 60-75% of the total cholesterol

25. Cholesterol 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

26. Factors 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 important • smoking: 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) • 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.

27. Triglycerides • 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.

28. Special 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.

29. Normal troponin levels 12 hours after chest pain has started mean a heart attack is unlikely

31. 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.