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Investigation of hyperlipidaemia

Investigation of hyperlipidaemia. Dr. S Homathy. Properties of lipids. 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

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Investigation of hyperlipidaemia

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  1. Investigation of hyperlipidaemia Dr. S Homathy

  2. Properties of lipids • Hydrophobic • High-energy food • For cell membranes, steroid hormones • Some lipids essentially exogenous

  3. Lipo-protein structure • Fat globule in water • Central hydrophobic core Triglycerides Esterified cholesterol • Outer shell Apoproteins Phospholipids Non-esterified cholesterol

  4. Types of lipo-proteins • High density (HDL) • Low density (LDL) • Very low density (VLDL) • Intermediate density (IDL) • Chylomicrons

  5. Primary Functions • HDL -Cholesterol from tissue to liver • LDL -Cholesterol to tissue • VLDL -Endogenous triglycerides • IDL -Transient form • Chylomicron -Exogenous triglycerides

  6. Broad basedly … • HDL = GOOD Cholesterol • LDL = BAD Cholesterol

  7. Composition of lipoproteins • HDL -50% proteins • LDL -55% Cholesterol • VLDL -55% Triglycerides • Chylomicron -90% Triglycerides

  8. Apoproteins in lipoproteins • HDL - A, C, E • LDL - B • VLDL - B, C, E. • Chylomicron - A, B, (C, E.)

  9. Electrophoretic mobility of lipoproteins • HDL - alpha • LDL - beta • VLDL - pre-beta • Chylomicron - origin

  10. Reference method for measurement of lipoproteins • ULTRA CENTRIFUGATION • Lipo protein floatation rate measured in Svedberg units

  11. Laboratory investigations • Serum total cholesterol • Serum lipid profile • Apo lipoprotein levels • Lipid electrophoresis • Special tests –geno typing

  12. 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.

  13. Secondary causes of hyperlipidaemia • Diabetes mellitus • Hypothyroidism • Nephrotic syndrome • Obstrucive jaundice • Alcohol abuse (Tg)

  14. 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

  15. 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

  16. Lipid profile • Measure Total Cholesterol HDL Cholesterol Triglycerides • Calculate LDL Cholesterol Cardiac risk ratio

  17. 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)

  18. Cardiac risk ratio • Total cholesterol / HDL cholesterol • > 5 is unfavourable • Apo A1 / Apo B ratio

  19. Interpretation • Total Cholesterol <200 Desirable 200-239 Borderline high  240 High

  20. LDL Cholesterol <100 Optimal 100-129 Near normal or above normal 130-159 Border line high 160-189 High 190 Very high

  21. HDL Cholesterol <40 Low >60 High

  22. Triglicerides <150 Normal 150-199 Borderline high 200-499 High  500 Very high

  23. Apolipoprotein levels • Apolipoprotein A 1- reflects HDL • Apolipoprotein B - reflects LDL • Apolipoprotein a - independent risk factor for MI

  24. Lipid electrophoresis • Serum electrophoresis is done • Stain with a lipid staining dye • Fredrickson’s Classification based on this.

  25. Fredrickson’s classification of hyperlipidaemia • TypePatternLipoproteins I origin chylomicrons II a b-lipoprotein LDL II b pre b & b VLDL + LDL III broad b IDL IV pre-b VLDL V origin & pre b Chylo + VLDL

  26. Special tests • Apo E genotyping using PCR technique

  27. Conversion factors • Cholesterol mg/dl / 38.6 = mmol/l • Triglyceride mg/dl / 88.5 = mmol/l

  28. Summary • Screening test Total Cholesterol • Confirming test Lipid profile • Phenotyping Lipid electrophoresis • Geno typing PCR technology • Monitoring tests Lipid profile

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