INTRODUCTION TO LABORATORY MEDICINE

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)

LIPOPROTEINS COMPOSITIONS

COMPOSITION OF LIPOPROTEINS

Class Diameter (nm)

 % protein

 % cholesterol

 % phospholipid

 % triacylglycerol& cholesterol ester

HDL 5–15 33 30 29 4LDL 18–28 25 50 21 8IDL 25–50 18 29 22 31VLDL 30–80 10 22 18 50Chylomicrons 100-1000 <2 8 7 84

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.

CHYLOMICRON STRUCTURE

LIPOPROTEIN 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

CARDIAC PROFILECardiac 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

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

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

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

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

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

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

FLIPPED LDHAn 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

INCREASED 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 18-30 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 – 25-90 IU/mL b. Female – 10-70 IU/mL

CHOLESTEROL

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

cholesterol

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

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.

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.

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.

Test Sensitivity and specificity

Troponin testThe 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.