investigation of hyperlipidaemia dr. s homathy. properties of lipids hydrophobic high-energy food...
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Investigation of hyperlipidaemia
Dr. S Homathy
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Properties of lipids
• Hydrophobic
• High-energy food
• For cell membranes, steroid hormones
• Some lipids essentially exogenous
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Lipo-protein structure
• Fat globule in water• Central hydrophobic core
TriglyceridesEsterified cholesterol
• Outer shellApoproteinsPhospholipidsNon-esterified cholesterol
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Types of lipo-proteins
• High density (HDL)
• Low density (LDL)
• Very low density (VLDL)
• Intermediate density (IDL)
• Chylomicrons
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Primary Functions
• HDL -Cholesterol from tissue to liver
• LDL -Cholesterol to tissue
• VLDL -Endogenous triglycerides
• IDL -Transient form
• Chylomicron -Exogenous triglycerides
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Broad basedly …
• HDL = GOOD Cholesterol
• LDL = BAD Cholesterol
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Composition of lipoproteins
• HDL -50% proteins
• LDL -55% Cholesterol
• VLDL -55% Triglycerides
• Chylomicron -90% Triglycerides
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Apoproteins in lipoproteins
• HDL - A, C, E
• LDL - B
• VLDL - B, C, E.
• Chylomicron - A, B, (C, E.)
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Electrophoretic mobility of lipoproteins
• HDL - alpha
• LDL - beta
• VLDL - pre-beta
• Chylomicron - origin
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Reference method for measurement of lipoproteins
• ULTRA CENTRIFUGATION
• Lipo protein floatation rate measured in Svedberg units
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Laboratory investigations
• Serum total cholesterol
• Serum lipid profile
• Apo lipoprotein levels
• Lipid electrophoresis
• Special tests –geno typing
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Total cholesterol
• Usually fasting
• Non-fasting accaptable for screening
• <200 mg/dl (5.2 mmol/l) is desirable.
• >200 mg/dl (5.2 mmol/l) proceed to a lipid profile.
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Secondary causes of hyperlipidaemia
• Diabetes mellitus
• Hypothyroidism
• Nephrotic syndrome
• Obstrucive jaundice
• Alcohol abuse (Tg)
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Lipid Profile
• Fast for 10 – 12 hours.• Normal lipid diet, constant weight• Not on drug affecting lipids (OCP)• Not on lipid lowering drugs unless being
monitored.• No stress (3 months after MI)• Standardised collection procedure
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Overnight serum
• Observe after keeping fasted serum in a test tube at 4C for 18 hours.
• Milky layer on top -chylomicrons
• Turbid serum -VLDL
• Clear -Normal / LDL
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Lipid profile
• Measure Total Cholesterol
HDL Cholesterol
Triglycerides
• Calculate LDL Cholesterol
Cardiac risk ratio
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Friedewald formula
• Total cholesterol = HDL + LDL + VLDL
• VLDL = Tg(in mg/dl) / 5
= Tg (in mmol/l) / 2.2
• Formula not valid if Triglycerides are > 400 mg/dl (4.5 mmol/l)
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Cardiac risk ratio
• Total cholesterol / HDL cholesterol
• > 5 is unfavourable
• Apo A1 / Apo B ratio
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Interpretation
• Total Cholesterol
<200 Desirable
200-239 Borderline high
240 High
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LDL Cholesterol
<100 Optimal
100-129 Near normal or
above normal
130-159 Border line high
160-189 High
190 Very high
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<40 Low
>60 High
HDL Cholesterol
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Triglicerides
<150 Normal
150-199 Borderline high
200-499 High
500 Very high
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Apolipoprotein levels
• Apolipoprotein A 1- reflects HDL
• Apolipoprotein B - reflects LDL
• Apolipoprotein a - independent risk factor for
MI
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Lipid electrophoresis
• Serum electrophoresis is done
• Stain with a lipid staining dye
• Fredrickson’s Classification based on this.
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Fredrickson’s classification of hyperlipidaemia
• Type Pattern LipoproteinsI origin chylomicronsII a b-lipoprotein LDLII b pre b & b VLDL + LDLIII broad b IDLIV pre-b VLDLV origin & pre b Chylo + VLDL
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Special tests
• Apo E genotyping
using PCR technique
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Conversion factors
• Cholesterol mg/dl / 38.6 = mmol/l
• Triglyceride mg/dl / 88.5 = mmol/l
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Summary
• Screening test Total Cholesterol
• Confirming test Lipid profile
• Phenotyping Lipid electrophoresis
• Geno typing PCR technology
• Monitoring tests Lipid profile