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2.2 Clinical Chemistry > Lipids - Laboratory Tests > Flashcards

Lipids - Laboratory Tests Flashcards

1
Q

What does a lipoprotein profile measure?

A

It measures the level of cholesterol in the blood

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2
Q

What are the two types of lipid profiles?

A

Fasting lipid profile

Random lipid profile

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3
Q

What tests may be included in a random lipid profile?
(2)

A

Triglycerides
Total cholesterol

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4
Q

What may be measured in the fasting lipid profile

A

HDL
LDL
Triglycerides
Total Cholesterol

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5
Q

What is the common method to detect cholesterol

A

CHOD-PAP method

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6
Q

What is the CHOD PAP method?
(5)

A

CHOD = cholesterol

P -> peroxidase

AP -> aminoantipyrine

It’s a coupled assay

It generates a coloured product, quinoneimine

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7
Q

What is the first reaction in the CHOD-PAP method

A

Cholesteryl Ester is converted to Free cholesterol and fatty acids by Cholesteryl Esterase

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8
Q

What converts cholesteryl esters to free cholesterol and fatty acids

A

Cholesteryl esterase

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9
Q

What is the second step in the CHOD-PAP assay

A

The free cholesterol + O2 is converted to 4-cholesten-3-one + H2O2 by cholesterol oxidase

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10
Q

What converts free cholesterol + O2 to 4-cholesten-3-one + H2O2?

A

Cholesterol oxidase

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11
Q

What is the third step of the CHOD-PAP assay?

A

2H2O2 + aminophenazone + phenol is converted into quinoneimine + 4H2O by peroxidase

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12
Q

What converts 2H2O2 + aminophenazone + phenol to quinoneimine + 4H2O?

A

Peroxidase

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13
Q

What is quinoneimine?

A

A red chromogen measured at 500nm

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14
Q

What does the cholesterol oxidase enzyme work on?
(2)

A

It accepts all sterols which have a 3B-hydroxyl group as substrates

Cholesterol is a 3B-hydroxy-cholest-5-ene

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15
Q

Give some examples of substrates for cholesterol oxidase

A

Plant sterols
Some steroid hormones
Cholesterol oxidation products

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16
Q

Why is the CHOD-PAP method considered biased?

A

Its biased towards slightly higher results compared to the definitive analysis method (isotope-dilution mass spectrometry)

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17
Q

What is the definitive analysis method for cholesterol

A

Isotope-dilute mass spectrometry

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18
Q

What are two alternative cholesterol assays other than the CHOD-PAP?

A

Lieberman-Burchard Reaction (CDC reference method)

Amplex red

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19
Q

Write about the Lieberman-Burchard reaction is a chemical method for cholesterol determination

A

Produces a blue-green colour with intensity proportional to the concentration of cholesterol

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20
Q

Why is the Lieberman-Burchard reaction?
(2)

A

Reagent is not very stable and it is best to use it fresh

The reagent also contains concentrated acids and is not particularly ‘user friendly’

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21
Q

Write about the amplex red assay
(4)

A

Similar to the CHOD-PAP method

CHOD is used to generate H2O2 but this is detected with amplex red rather than AAP

Amplex red is converted to the fluorescent resorufin in the presence of peroxidase and H2O2

More sensitive assay

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22
Q

List some variables in cholesterol testing
(5)

A

Age and gender -> males greater than females, this increases with age

Within day variation of between 2 and 3%

Seasonal variation of 3-5%

Venous stasis causing an increase between 10-15% within 5 minutes of stasis

Trauma can decrease lipid levels for several weeks

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23
Q

How are TAGs measured?
(3)

A

TAG ASSAY

A complex coupled assay with four separate enzyme reactions

It measures the concentration of free glycerol via generation of a quinoneimine product

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24
Q

What is the first step in the TAG ASSAT

A

Triglycerol + 3H2O

Converted to Glycerol + 3 fatty acids

By Lipase

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25
What is the second step in the TAG assay
Glycerol + ATP Converted to glycerol-3-phosphate + ADP By Glycerol Kinase
26
What is the third step in the TAG Assay
Glycerol-3-phosphate + O2 Converted to Dihydroxyoxyacetone-P + H2O2 By Glycerol-P-Oxidase
27
What is the fourth step of the TAG assay
H2O2 + Aminophenazone + Chlorophenol converted to Quinoemimine + HCL + 4H2O By Peroxidase
28
What are the four enzymes in the TAG Assay
Lipase Glycerol Kinase Glycerol-P-Oxidase Peroxidase
29
Why is investigation of lipoprotein important?
Due to the association of particular types of lipoprotein with cardiovascular disease
30
How are lipoproteins investigates (4)
Number of lipoprotein analysis e.g. NMR Overall pattern of lipoproteins e.g. electrophoresis Lipoprotein specific lipid content e.g. gel filtration Apolipoprotein concentration e.g. ELISA
31
How is HDL-Cholesterol specific lipid measurement measured? (3)
Based on the use of reagents which cause LDL-Cholesterol to precipitate In a fasting sample should only leave HDL-Cholesterol Thus can use the normal assays on the supernatant and calculate the LDL as the difference between the Total Cholesterol and the HDL-C (Friedewald Formula)
32
What is the Friedewald formula?
LDL Cholesterol = Cholesterol - (HDL + VLDL) VLDL = TAG/2.2
33
When can the Friedward Formula not be used to calculate LDL cholesterol
When the TAG is greater than 4.5 mmol/L
34
How are normal ranges for lipids determined (3)
Range depends on the populations e.g. 20% higher cholesterol in Western populations vs Asian population Levels change with age - gradual increase
35
What are the normal recommendations for lipids? (3)
Cholesterol should be less than 5 mmol/L LDL-C should be less than 3.4 mM TAG should be less than 1.5 mmol/L
36
What does a risk assessment involve (3)
Evaluate the risk of heart disease based on measurement of blood lipid levels Algorithms of varying complexity evaluate the 10 year risk of an event These risk assessments may inform the decision to start treatment
37
Give six examples of factors measured in a risk assessment
Total cholesterol HDL-C LDL-C TAG Smoker Blood pressure
38
Define dyslipidemia (2)
A consequence of abnormal lipoprotein metabolism Lipid levels above the recommended levels
39
What are the four types of dyslipidemia
Elevated Total Cholesterol Elevated Low-density lipoproteins Elevated triglycerides Decreased High-density lipoproteins
40
What are the two types of dyslipidaemia
Primary and secondary
41
What is primary dyslipidaemia (2)
Single or multiple gene mutation Results in disturbances of LDL, HDL and TAG Production or clearance
42
What is secondary dyslipidaemia? (2)
Sedentary lifestyle Excessive consumption of cholesterol - saturated fats and trans-fatty acids
43
What is the common type of dyslipidaemia in Ireland
Secondary
44
Give some examples of lipid abnormalities
Hypercholesterolaemia
45
Why is hypercholesterolaemia dangerous?
Its a major risk factor for coronary heart disease
46
How does hypercholesterolemia cause heart disease?
Cholesterol is deposited along walls of blood vessels LDL is a key player in this process Plaque ruptures and clot forms -> this impedes blood flow, tissues starved of oxygen and die which can cause angina or heart attack
47
What are the main major risk factors for coronary heart disease? (4)
Smoking High blood pressure High blood cholesterol Physical inactivity There are also some genetic components
48
What is the most common classification system used for primary Hyperlipidemia?
Based on Fredrickson Defined categories based on the spectrum of changes in blood lipids
49
What is Fredrickson Type I primary hyperlipidemia (4)
Chylomicron Deficiency of lipoprotein lipase of apolipoprotein CII (which activates LPL) An inability to clear chylomicrons from the circulation Since chylomicrons are TAG rich it leads to profound hypertriglyceridemia
50
What is a tell tale sign of Chylomicron Syndrome (Fredrickson Type I) Primary hyperlipidemia
High levels of chylomicron TAGs leads to hepatomegaly and eruptive xanthomata The lipids essentially burst out of the skin
51
How is Chylomicron Syndrom (Fredrickson Type I) Primary Hyperlipidemia syndrome treated?
Treated with a low fat diet In ApoCII deficient forms plasma infusion may be used to temporarily replace ApoCII levels and thus LPL activity
52
What is Fredrickson Type IIa Primary Hyperlipidemia also called?
Familial Hypercholesterolemia
53
What causes FT IIa Primary Hyperlipidemia/ Familial Hypercholesterolemia (6)
Deficiency of LDL-receptor function Typically a mutation in the receptor Can also have deficits in cytoplasmic adaptor proteins This prevents LDL from being internalised i.e. it remains in plasma 1;500 people carry the mutation LDL cannot be removed from the plasma
54
What are some characteristic traits of FT IIa Primary Hyperlipidemia/ Familial Hypercholesterolemia?
Cholesterol levels elevated TAG levels generally show minor changes
55
What are some symptoms of FT IIa Primary Hyperlipidemia/ Familial Hypercholesterolemia?
Tendon Xanthoma Corneal Arci
56
How is FT IIa Primary Hyperlipidemia/ Familial Hypercholesterolemia treated
In heterozygous FH LDL-R is upregulated -> more receptors with residual function will cleave LDL from the blood In homozygous FH may need plasma apheresis
57
What is Fredrickson Type III called?
Hyperlipoproteinemia
58
What causes hyperlipoproteinemia
Its associated with the E2 variant of APO-E
59
What does FS Type III result in? (4)
Impaired catabolism of IDL IDL is not cleared as well from the plasma Causes accumulation of VLDL remnants It is often precipitated by conditions which increase VLDL
60
What exactly happens in secondary hyperlipidemia
Diseases lead to increases in either cholesterol or TAG as a secondary effect
61
Give some examples of secondary hyperlipidemias
Predominant hypercholesterolaemia Predominant hypertriglyceridaemia
62
What may cause prominant hypercholesterolaemia (2)
Cholestasis Primary hypothyroidism
63
What may cause predominant hypertriglyceridemia? (3)
Obesity Diabetes Metabolic Syndrome
64
How is hypercholesterolemia treated (3)
Therapies target cholesterol absorption or synthesis Dietary intervention is essential - cut out saturated fats, eggs etc (absorption), use plant stanol enriched spreads (absorption) Theres not much you can do from a dietary perspective to stop cholesterol synthesis -> drugs
65
What drugs are used to treat hypercholesterolemia? (4)
Drug therapies block either synthesis or absorption Statin class of drugs competitively inhibit cholesterol synthesis -> lipitor, zocor Eztimibe blocks cholesterol absorption (bile acid binding resin) Can be used in combination

2.2 Clinical Chemistry (28 decks)

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