Measurements of Cholesterol Flashcards

1
Q

Functions of cholesterol (4)

A

Membrane component
Steroid synthesis
Bile acid/salt precursor
Vitamin D precursor

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2
Q

What assays are available for cholesterol measurement?

A

Total serum cholesterol assay

Use of cholesterol dehydrogenase

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3
Q

How does the assay for cholesterol work?

A

Total Serum Cholesterol Assay

1) Cholesterol ester —> cholesterol + fatty acid (cholesterol esterase)
2) Cholesterol –> Ketone (cholesterol oxidase) + H2O2

3) H2O2 + ADPH –> Resorufin
(horseradish peroxidase)

Resorufin = fluorescence

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4
Q

How can cholesterol dehydrogenase be used to measure cholesterol?

A

Cholesterol undergoes oxidation

  • NAD+ –> NADH
  • absorbance of NADH can be measured (linear relationship)
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5
Q

What constitutes as high risk cholesterol when measuring using the total serum cholesterol assay?

A

Around > 200mg/dL

Increased values as age increases

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6
Q

How do cholesterol testing devices work?

A

Electrochemical assays (biosensor)

  • cholesterol oxidase
  • current is generated
  • measured as a value
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7
Q

What is specifically measured in total serum cholesterol assay?

A

VLDL + LDL + HDL

Hard to distinguish due to same size (difference in lipid proportion)

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8
Q

How are HDLs calculated?

A

HDL does not contain apoprotein B
- VLDL, LDL and chyclomicrons do

Addition of reagent sulphated-a-cyclodextrin blocks apoprotein B, effectively excluding everything but HDL
- Only HDL will react with the cholesterol enzyme reagent thus allows estimate

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9
Q

What is detected in pregnancy tests?

A

HCG - human chorionic gonadotropin (elevated levels)

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10
Q

What type of assay is used in pregnancy testing?

A

Chromatographic immunoassay

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11
Q

How do pregnancy tests work

A

LATERAL FLOW DEVICE

Sample of urine travels up absorbent element (capillary action)

  • attach to mobilised antibodies labelled with dye (form antibody-antigen complex I)
  • carried by sample fluid up the lateral flow wick
  • attaches to secondary antibodies specific to HCG which are immobilised, thus producing a coloured line
  • 1st coloured line shows positive result
  • moves further to 3rd zone where reacts with anti-antibody: coloured line forms independent of HCG present (control zone to ensure test is working)
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