LIPIDS AND CARDIAC MARKERS

Question 1

What are lipoproteins ?

Answer 1

Proteins that transport lipids in the plasma

Question 2

What are fatty acids ?

Answer 2

• linear hydrocarbon chains that terminate in a carbonyl group
• oxidation of free fatty acids = acetyl-CoA enters kerbs cycle for ATP

Question 3

What are triglycerides ?

Answer 3

• 3 fatty acid molecules + glycerol
• neutral lipids

Question 4

What is cholesterol ?

Answer 4

• amphipathic
• esterified cholesterol (cholesteryl ester) is conjugated to fatty acids = neutral lipid
• used to synthesize many hormones

Question 5

What is phospholipids ?

Answer 5

• amphipathic molecule
• two esterified fatty acids, glycerol, an phospholipid group
• found in cell membrane

Question 6

What are apolipoproteins ?

Answer 6

• amphipathic

Question 7

How are lipoproteins classified ?

Answer 7

By density (from least dense):
- chylomicrons
- VLDL
- IDL
- LDL
- HDL
- lipoprotein

Question 8

As density of lipoproteins increases, the proportion of triglycerides __, and the proportion of cholesteryl ester __.

Answer 8

As density of lipoproteins increases, the proportion of triglycerides DECREASES, and the proportion of cholesteryl ester INCREASES.

Question 9

What are chylomicrons ?

Answer 9

• transport dietary lipids (apolipoprotein B-48) to the liver and peripheral cells
• largest and least dense lipoprotein
• forms the creamy layer on top of serum

Question 10

What are VLDL ?

Answer 10

Very Low Density Lipoproteins:
- produced in liver
- carries endogenous triglycerides from liver to peripheral cells (used as energy during fasting)
Ie. apolipoprotein B-100

Question 11

What are LDL ?

Answer 11

Low Density Lipoproteins:
- formed from lipolysis of VLDL
- readily taken up by liver and peripheral cells
- LDL that move into extracellular space of blood vessel walls and ingested by macrophages = foam cells that can develop into atherosclerotic plaques
Ie. apolipoprotein B-100

Question 12

What are HDL ?

Answer 12

High Density Lipoproteins:
- synthesized in liver and intestines
- removes cholesterol away from peripheral cells back to the liver
- anti-atherogenic
Ie. apolipoprotein A-1

Question 13

Clinical significance of abnormal [lipid]

Answer 13

• coronary heart disease; narrowing of blood vessels
• atherosclerosis; cholesterol deposits on vessel walls, macrophage invasion, and plaque formation = myocardial infarction, strokes, peripheral vascular disease

Question 14

Interferences of Triglycerides enzymatic assay

Answer 14

• endogenous free glycerol (corrected by reagent blank)
• bilirubin, ascorbic acid/ vitamin C (corrected by enzymes)
• hemolysis = false positive

Question 15

Sample types for Triglyceride enzymatic assay ?

Answer 15

• 12-hour fasting
• no alcohol 24 hours prior testing
• lying down vs standing, exercise = false increase
• nicotine = false increase

Question 16

Interferences of Total Cholesterol Enzymatic Assay

Answer 16

• bilirubin and ascorbic acid/ vitamin C reacts with H2O2 = false decrease
• hemolysis = false positive

Question 17

Sample type for Total Cholesterol Enzymatic Assay ?

Answer 17

• 12-hour fasting
• laying down vs standing, exercise = false decrease
• nicotine = false increase
• prolonged tourniquet use = false increase

Question 18

Why is the HDL cholesterol method advantageous ?

Answer 18

• homogenous assay
• no pretreatment/ centrifugation required

Question 19

How does the HDL cholesterol method work ?

Answer 19

• detergent solubilizes only HDL lipoproteins and releases HDL cholesterol = reacts with cholesterol esterase/ oxidase to produce a chromogen
• same detergent also inhibits reactions with LDL, VLDL, and chylomicron lipoproteins by adsorbing to surfaces
• change in absorbance = DIRECTLY PROPORTIONAL to [cholesterol]

Question 20

Friedewald formula

Answer 20

LDL Cholesterol = Total cholesterol - [Triglyceride /2.2] - [ HDL cholesterol]

Question 21

What is a MI ?

Answer 21

Myocardial Infarction:
- result of an obstruction in circulatory pathway of heart = necrosis of heart muscle

Question 22

Cardiac marker of MI

Answer 22

Troponin

Question 23

What is congestive heart failure ?

Answer 23

• heart is unable to pump blood to maintain oxygenation of tissues
• characterized by edema due to sodium and water retention, and lack of oxygen

Question 24

Cardiac marker for congestive heart failure

Answer 24

• B-type natriuretic peptide (BNP)
• NT-pro-BNP

Question 25

What are troponins ?

Answer 25

• cardiac marker for MI
• TnC, TnT, TnI
• part of the actin-myosin contractile unit of muscle

Question 26

Which isoforms of troponin are cardiac-specific ?

Answer 26

TnT and TnI

Question 27

How are TnT and TnI measured ?

Answer 27

• cardiac-specific troponins are detectable via immunoassay
• TnI* and TnT approximately rise 2-6 hours after onset of symptoms
• collection of TnI sample at 0 hours and 6 hours later to rule out MI
• remains elevated 4-10 days after MI

*more specific to MI

Question 28

Interference for TnI testing

Answer 28

• heparin
• heterophilic an autoantibodies
• hemolysis/ fibrin
• rheumatoid factors

Question 29

What are B-type Natriuretic Peptides ?

Answer 29

• hormones secreted by ventricles of the heart
• preproBNP cleaved into proBNP cleaved into N-terminal portion (NT-proBNP) and C terminal (active BNP)
• BNP is a marker of cardiac stretch
• used for identifying severe congestive heart failure and for risk assessment

Question 30

Sample type for BNP and NT-proBNP testing

Answer 30

BNP: EDTA in PLASTIC tube

NT-proBNP: serum or heparin plasma in a glass or plastic tube

Question 31

How are both BNP and NT-proBNP measured ?

Answer 31

Via immunoassay

Question 32

BNP level to diagnose heart failure

Answer 32

> 500 pg/mL

Question 33

What are CRPs ?

Answer 33

C Reactive Protein:
- values above normal but below those seen in infection indicate atherosclerosis, a factor for heart disease

Question 34

How are CRPs measured ?

Answer 34

High sensitivity C reactive protein assay (hsCRP assay)