Investigation of hyperlipidaemia
Dr. S Homathy
Properties of lipids
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Hydrophobic
High-energy food
For cell membranes, steroid hormones
Some lipids essentially exogenous
Lipo-protein structure
• Fat globule in water
• Central hydrophobic core
Triglycerides
Esterified cholesterol
• Outer shell
Apoproteins
Phospholipids
Non-esterified cholesterol
Types of lipo-proteins
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High density (HDL)
Low density (LDL)
Very low density (VLDL)
Intermediate density (IDL)
Chylomicrons
Primary Functions
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HDL
-Cholesterol from tissue to liver
LDL
-Cholesterol to tissue
VLDL -Endogenous triglycerides
IDL
-Transient form
Chylomicron -Exogenous triglycerides
Broad basedly …
• HDL = GOOD Cholesterol
• LDL = BAD Cholesterol
Composition of lipoproteins
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HDL
LDL
VLDL
Chylomicron
-50% proteins
-55% Cholesterol
-55% Triglycerides
-90% Triglycerides
Apoproteins in lipoproteins
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HDL
LDL
VLDL
Chylomicron
- A, C, E
-B
- B, C, E.
- A, B, (C, E.)
Electrophoretic mobility of
lipoproteins
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HDL
LDL
VLDL
Chylomicron
- alpha
- beta
- pre-beta
- origin
Reference method for measurement
of lipoproteins
• ULTRA CENTRIFUGATION
• Lipo protein floatation rate measured in
Svedberg units
Laboratory investigations
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Serum total cholesterol
Serum lipid profile
Apo lipoprotein levels
Lipid electrophoresis
Special tests –geno typing
Total cholesterol
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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.
Secondary causes of hyperlipidaemia
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Diabetes mellitus
Hypothyroidism
Nephrotic syndrome
Obstrucive jaundice
Alcohol abuse (Tg)
Lipid Profile
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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
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
Lipid profile
• Measure Total Cholesterol
HDL Cholesterol
Triglycerides
• Calculate
LDL Cholesterol
Cardiac risk ratio
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)
Cardiac risk ratio
• Total cholesterol / HDL cholesterol
• > 5 is unfavourable
• Apo A1 / Apo B ratio
Interpretation
• Total Cholesterol
<200
Desirable
200-239
Borderline high
 240
High
LDL Cholesterol
<100
100-129
Optimal
Near normal or
above normal
130-159
160-189
190
Border line high
High
Very high
HDL Cholesterol
<40
>60
Low
High
Triglicerides
<150
150-199
200-499
 500
Normal
Borderline high
High
Very high
Apolipoprotein levels
• Apolipoprotein A 1- reflects HDL
• Apolipoprotein B - reflects LDL
• Apolipoprotein a - independent risk
factor for MI
Lipid electrophoresis
• Serum electrophoresis is done
• Stain with a lipid staining dye
• Fredrickson’s Classification based on this.
Fredrickson’s classification of
hyperlipidaemia
• Type
I
II a
II b
III
IV
V
Pattern
Lipoproteins
origin
chylomicrons
b-lipoprotein
LDL
pre b & b
VLDL + LDL
broad b
IDL
pre-b
VLDL
origin & pre b Chylo + VLDL
Special tests
• Apo E genotyping
using PCR technique
Conversion factors
• Cholesterol mg/dl / 38.6 = mmol/l
• Triglyceride mg/dl / 88.5 = mmol/l
Summary
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Screening test Total Cholesterol
Confirming test
Lipid profile
Phenotyping
Lipid electrophoresis
Geno typing
PCR technology
Monitoring tests
Lipid profile