DISORDERS OF LIPID METABOLISM_ABUAD.docx

**[DISORDERS OF LIPID METABOLISM]** Dr Ademola Adelekan Department of Chemical Pathology College of Medicine & Health Sciences Afe Babalola University, Ado-Ekiti/Federal Teaching Hospital, Ido-Ekiti **[Introduction]** There are several rare, inherited metabolic diseases associated with the acc...

**[DISORDERS OF LIPID METABOLISM]** Dr Ademola Adelekan Department of Chemical Pathology College of Medicine & Health Sciences Afe Babalola University, Ado-Ekiti/Federal Teaching Hospital, Ido-Ekiti **[Introduction]** There are several rare, inherited metabolic diseases associated with the accumulation of lipids in tissues, and others in which plasma lipoprotein concentrations are reduced. Secondary lipid disorders are those arising as a consequence of a disease, drug treatment, or defective nutrition. The commonest disorders are the hyperlipidaemias. **[Classification of lipid disorders]** 1. Hyperlipidaemias 2. Hypolipidaemias **CLASSIFICATION OF HYPERLIPIDAEMIAS** 1. Fredrickson Classification: Type I -V 2. Diagnostic Classification: Primary (Familial) or Secondary (Acquired) disorders 3. Based on type of lipid predominantly elevated: Hypercholesterolaemia, Hypertriglyceridaemia **Fredrickson Classification:** A widely used classification is that of Fredrickson, one of the pioneers of clinical lipidology, which has been adopted by the World Health Organization (WHO). This classification originally emphasized the observed lipoprotein pattern or phenotype, but now is expressed mainly in terms of lipid measurements. It recognizes five types, numbered 1 to 5~~.~~ Type 1 is associated with marked hyperchylomicronaemia. It is caused by a deficiency of\ lipoprotein lipase or a deficiency of its activator, apoprotein C2. There are two subtypes of type 2. Type 2a implies hypercholesterolaemia without hypertriglyceridaemia and includes monogenic inherited disorders, such as familial hypercholesterolaemia, but is more often polygenic in origin. Type 2b implies combined hypercholesterolaemia with increased amounts of circulating TGs. It is the pattern seen in familial combined dyslipidaemia, but there are several other causes, including secondary hyperlipidaemia that is associated with the overproduction of VLDL. Type 3 lipid disorder is associated with variants of apoE protein, which leads to an accumulation of abnormal IDL particles. This disorder may be suspected when cholesterol and TGs increase in equimolar amounts, reflecting the cholesterol enrichment of IDL. Type 4 is associated with hypertriglyceridaemia that implies increases in VLDL without chylomicrons. Type 5 is associated with marked hypertriglyceridaemia and increased VLDL and chylomicrons. The primary cause may be increases in VLDL and IDLs that interfere with the receptor-mediated removal of chylomicrons. Chylomicrons can easily be identified by their ability to float to the surface of plasma as a creamy layer when it is stored at 4^o^C. However, chylomicrons are always present when the concentration of TGs is \> 10 mmol/L. The Frederickson classification does not include the combined dyslipidaemia associated with\ the metabolic syndrome with abnormally dense LDL and does not include Lp(a) or HDL abnormalities, nor does it address the secondary hyperlipidaemias. It gives little clue as to the aetiology of the disorder; indeed, all of the phenotypes can be either primary or secondary. Furthermore, the Fredrickson type can change as a result of dietary or drug intervention. Although widely used for many years, several flaws became apparent: with some inherited\ hyperlipidaemias, the same genotype can be expressed as more than one phenotype in different\ individuals; similarly, the phenotypes associated with individual secondary hyperlipidaemias can vary; in both inherited and secondary hyperlipidaemias, drug treatment can alter the phenotype, and, finally, the classification takes no account of HDL-C. **Diagnostic Classification:** **[Primary hyperlipidaemias]** 1. Chylomicron syndrome 2. Familial hypercholesterolaemia 3. Familial defective apoB~3500~ 4. Familial combined hyperlipidaemia 5. Familial hypertriglyceridaemia 6. Type III hyperlipoproteinaemia (familial dysbetalipoproteinaemia or broad β-hyperlipidaemia) 7. Polygenic hypercholesterolaemia 8. Hyperalphalipoproteinaemia **Chylomicron syndrome:** This can be due to **familial lipoprotein lipase deficiency**, an **autosomal recessive** disorder affecting about 1 in 1,000,000 people. The **gene for lipoprotein lipase is found on chromosome 8**, and genetic studies have shown insertions or deletions within the gene. Lipoprotein lipase is involved in the exogenous lipoprotein pathway by hydrolysing chylomicrons to form chylomicron remnants, and also in the endogenous pathway by converting VLDL to IDL particles. Presentation as a child with abdominal pain (often with acute pancreatitis) is typical. There is probably no increased risk of coronary artery disease. Gross elevation of plasma triglycerides due to the accumulation of uncleared chylomicron particles occurs. Lipid stigmata include eruptive xanthomata, hepatosplenomegaly and lipaemia retinalis. Other variants of the chylomicron syndrome include circulating inhibitors of lipoprotein lipase and deficiency of its physiological activator apoC2. Apolipoprotein C2 deficiency is also inherited as an autosomal recessive condition affecting about 1 in 1,000,000 people. The gene for apoC2 is located on chromosome 19 and mutations resulting in low plasma concentrations have been found. Treatment of the chylomicron syndrome involves a low-fat diet, aiming for less than 20 g of fat a day, if possible, although compliance on such a diet may be difficult. Some clinicians supplement the diet with medium-chain triglycerides and also give 1% of the total calorie intake as linoleic acid. In cases of apoC2 deficiency, fresh plasma may temporarily restore plasma apoC2 levels. Patients may show a type I or type V Fredrickson's phenotype. **Familial hypercholesterolaemia:** Usually inherited as an **autosomal dominant** trait. The inheritance of one mutant **gene that encodes for the LDL receptor** affects about 1 in every 500 people (more common in certain groups such as Afrikaners and French Canadians), resulting in impaired LDL catabolism and hypercholesterolaemia. At least **five types of mutation** of the LDL receptor have been described, resulting in reduced synthesis, failure of transport of the synthesized receptor to the Golgi complex within the cell, defective LDL binding or inadequate expression or defective recycling of the LDL receptor at the cell surface. Familial hypercholesterolaemia (FH) is defined as a plasma cholesterol concentration of \>7.5 mmol/L in an adult (\> 6.7 mmol/L in children under 16 years) or a plasma LDL-C concentration of \> 49mmol/L in an adult in the presence of tendon xanthoma. Possible FH is defined as a plasma cholesterol concentration of more than 7.5 mmol/L in an adult (\> 6.7 mmol/L in children under 16 years) or a plasma LDL-C concentration of \> 4.9 mmol/L in an adult, plus a family history of either an elevated plasma cholesterol concentration of \> 7.5 mmol/L in a first-degree or second-degree relative or myocardial infarction below the age of 50 years in a first-degree relative or below the age of 60 years in a second-degree relative. Typically, patients manifest severe hypercholesterolaemia, with a relatively normal plasma triglyceride concentration in conjunction with xanthomata, which can affect the back of the hands, elbows, Achilles tendons or the insertion of the patellar tendon into the pretibial tuberosity. Premature cardiovascular disease is often observed, along with premature corneal arci. Using the Fredrickson's classification, this condition has also been termed familial type IIa hyperlipoproteinaemia, although some patients may show a type IIb phenotype. Plasma HDL cholesterol concentration can vary in different individuals, although low concentrations may increase the likelihood of cardiovascular disease. It has been shown that in heterozygote FH there is more likely to be an increased amount of plasma Lp(a) in those subjects with cardiovascular disease. The diagnosis of FH is usually obvious from the markedly elevated plasma cholesterol concentration and the presence of tendon xanthomata in the patient or first-degree relation. The diagnosis may not be so clear cut in patients without the lipid stigmata. The treatment is usually with the HMG-CoA reductase inhibitors (statins). [Homozygous FH can be very severe.] There is a considerable risk of coronary artery disease, aortic stenosis and early fatal myocardial infarction before the age of 20 years. Florid xanthoma occurs in childhood including tendon, planar and cutaneous types. Atheroma of the aortic root may manifest before puberty, associated with coronary ostial stenosis. In homozygous FH, treatment to lower the plasma cholesterol concentration (which can be as high as 20 mmol/L or more) is essential in order to try to reduce the likelihood of sudden death due to coronary artery disease. Plasma exchange, LDL apheresis or heparin extracorporeal LDL precipitation (HELP) can be used in an attempt to remove the plasma LDL particles and thus reduce the plasma cholesterol concentration. There is a rare recessive form of FH and also a form of FH associated with increased proprotein convertase subtilisin/kexin type 9 (PCSK9) expression which regulates LDL receptors. **Familial defective apoB~3500~:** is due to a mutation in the **apoB gene** (located upon chromosome 2) resulting in a substitution of arginine at the 3500 amino acid position for glutamine. Apolipoprotein B is the ligand upon the LDL particle for the LDL receptor. It may be indistinguishable clinically from FH and is also associated with hypercholesterolaemia and premature coronary artery disease. The treatment is similar to that for heterozygote FH. **Familial combined hyperlipidaemia (FCH)**: may be inherited as an **autosomal dominant** trait. About 0.5% of the European population is affected, and there is an increased incidence of coronary artery disease in family members. The metabolic defect is unclear, although plasma apoB is often elevated due to increased synthesis; LDL and VLDL apoB concentration is increased. The synthesis of VLDL triglyceride is increased in FCH and there may also be a relationship with insulin resistance. Plasma cholesterol concentration is often between 6 - 9 mmol/L and plasma triglyceride between 2 - 6 mmol/L. The Fredrickson's phenotypes seen in this condition include IIa, IIb and IV. The diagnosis of FCH is suspected if there is a family history of hyperlipidaemia, particularly if family members show different lipoprotein phenotypes. There is often a family history of cardiovascular disease. However, the diagnosis can be difficult and it sometimes needs to be distinguished from FH (xanthomata are not usually present in FCH) and familial hypertriglyceridaemia (the IIa and IIb phenotypes are not usually found in familial hypertriglyceridaemia, although they are in FCH). Children with FCH usually show hypertriglyceridaemia and not the type IIa phenotype (unlike the situation found in FH). Unlike familial hypertriglyceridaemia, plasma VLDL particles are usually smaller in FCH. Dietary measures and, if indicated, either a statin or a fibrate may be used. **Familial hypertriglyceridaemia**: The exact metabolic defect is unclear, although overproduction of VLDL or a decrease in VLDL conversion to LDL is likely. It is often observed with **low HDL-C** concentration. LDL low, total cholesterol elevated or normal. The condition usually develops after puberty and is **rare in childhood**. There may be an increased risk of cardiovascular disease. Acute pancreatitis may also occur, and is more likely when the concentration of plasma triglycerides \> 10 mmol/L. Some patients show hyperinsulinaemia and insulin resistance. Dietary measures, and sometimes lipid-lowering drugs such as the fibrates or ω-3 fatty acids, are used to treat the condition. The Fredrickson's phenotype seen in this condition is IV. **Type III hyperlipoproteinaemia**: This condition is also called **familial dysbetalipoproteinaemia, broad β-hyperlipidaemia or remnant hyperlipoproteinaemia**. The underlying biochemical defect is one of a **reduced clearance of chylomicron and VLDL remnants**. The name broad b-hyperlipidaemia is sometimes used because of the characteristic plasma lipoprotein electrophoretic pattern that is often observed (the broad β-band that is seen being remnant particles). An association with Type III hyperlipoproteinaemia and homozygosity for apoE2 or variants of apoE2 has been described. Apolipoprotein E shows three common alleles, E2, E3 and E4, coded for on chromosome 19, which are important for the binding of remnant particles to the remnant receptor. The mechanism for the disorder seems to be that apoE2 -bearing particles have poor binding to the apoB/E (remnant) receptor and thus are not effectively cleared from the circulation. It is becoming apparent that it is not just inheriting the apoE2 genotype that is important in developing Type III hyperlipoproteinaemia. The prevalence of the apoE2 / E2 genotype is about 1 in 100 in the general population, yet only about 1 in 5000--10 000 individuals manifest type III hyperlipoproteinaemia. [A concurrent increase in plasma VLDL concentration also seems necessary for the condition to be expressed, such as might occur in diabetes mellitus, hypothyroidism or obesity (precipitants]). Some patients may show **either an autosomal recessive or a dominant mode of inheritance** of the condition. [The palmar striae (palmar xanthomata) are considered pathognomonic for the disorder], but tuberoeruptive xanthomata, typically on the elbows and knees, xanthelasma and corneal arcus have also been described in this condition. Peripheral vascular disease is a typical feature of this hyperlipidaemic disorder, as is premature coronary artery disease. Plasma lipid determination frequently reveals **hypercholesterolaemia and hypertriglyceridaemia, often in similar molar proportions** with plasma concentrations of around 9--10 mmol/L. **Plasma HDL-C concentration is usually low. Plasma LDL concentration may also be** low due to the fact that there is reduced conversion from IDL particles, although it may also be normal or elevated. Plasma lipoprotein electrophoresis can show the **classic type III picture** with a broad b-band composed of remnant particles, although this is not always present. An association of type III hyperlipoproteinaemia with homozygosity for apoE2 has been described, and thus apoE phenotyping or genotyping by a specialized laboratory can be useful, although some patients with broad β-hyperlipidaemia can show other apoE phenotypes or variants. Treatment consists of dietary measures, correcting the precipitating causes and either the statin or fibrate drugs. **Polygenic hypercholesterolaemia:** This is one of the most common causes of a raised plasma cholesterol concentration. This condition is the result of a complex interaction between multiple environmental and genetic factors (i.e. it is not due to a single gene abnormality, and it is likely that it is the result of more than one metabolic defect). There is usually either an increase in LDL production or a decrease in LDL catabolism. The plasma lipid phenotype is usually **either IIa or IIb Fredrickson's phenotype**. The [plasma cholesterol concentration is usually either mildly or moderately elevated. ] [An important negative clinical finding is the absence of tendon xanthomata], the presence of which would tend to rule out the diagnosis. Usually less than 10% of first-degree relations have similar lipid abnormalities, compared with FH or FCH in which about 50% of first-degree family members are affected. There may also be a family history of premature coronary artery disease. Individuals may have a high intake of dietary fat and be overweight. Treatment involves dietary intervention and sometimes the use of lipid-lowering drugs such as the statins. **Hyperalphalipoproteinaemia**: results in elevated plasma HDL-C concentration and can be inherited as an **autosomal dominant** condition or, in some cases, may show polygenic features. The total plasma cholesterol concentration can be elevated, with normal LDL-C concentration. [There is no increased prevalence of cardiovascular disease in this condition]; in fact, the contrary probably applies, with some individuals showing longevity. Plasma HDL concentration is thought to be cardioprotective, and individuals displaying this should be reassured. Other causes of raised plasma HDL-C concentrations are listed below. **Some causes of raised plasma high-density lipoprotein (HDL) cholesterol** 1. Primary (Hyperalphalipoproteinaemia, Cholesterol ester transfer protein deficiency) 2. Secondary (High ethanol intake, Exercise, Certain drugs, e.g. estrogens, fibrates, nicotinic acid, statins, phenytoin, rifampicin) **Summary of some primary hyperlipidaemias** **[Secondary hyperlipidaemias ]** They may present alone or sometimes concomitantly with a primary hyperlipidaemia. Probably less than 20% of cases of hyperlipidaemia are secondary to other disease. Patterns of abnormality tend to vary, even within a single disease; plasma cholesterol or triglycerides, or both, may be affected. Some of the causes of secondary hyperlipidaemia are listed below. Hypercholesterolaemia is often a marked feature of hypothyroidism and of the nephrotic syndrome; in these two disorders, there is increased plasma LDL. The immunosuppressive drugs ciclosporin and tacrolimus, and the protease inhibitors used in the treatment of HIV infection, also cause hypercholesterolaemia. Coronary artery disease tends to develop in those patients with long‐standing secondary hyperlipidaemia. Hypertriglyceridaemia secondary to other disease is most commonly due to diabetes mellitus or to excessive alcohol intake, and is also a feature of HIV infection. It may occur in chronic renal disease and in patients on oestrogen therapy or retinoids. Protease inhibitors cause hypertriglyceridaemia as  well as hypercholesterolaemia and this is superimposed on the dyslipdaemia seen in HIV infection. Lipoprotein X is an abnormal discoid particle rich in phospholipid and unesterified cholesterol. It contains albumin within its core and apolipoprotein C on its surface, but unlike LDL contains no apolipoprotein B and is not removed by the LDL receptor. It is cleared by the reticuloendothelial system and the kidneys. Its precursor is bile lipoprotein, and in cholestasis this spills over into the plasma, binding to albumin to form lipoprotein X. Chronic cholestasis (for example due to primary biliary cirrhosis or cholestasis of pregnancy) thus causes the accumulation of lipoprotein X. This particle is probably not atherogenic. The effects of alcohol on plasma lipids are complex. Regular drinking of small amounts increases plasma HDL without affecting other lipoprotein particles. Some heavy drinkers develop hypertriglyceridaemia due to increased plasma VLDL, possibly as a result of increased direction of fatty acid metabolism into triglyceride synthesis in the liver. The hyperlipidaemia secondary to diabetes mellitus is also complex. Increased plasma VLDL is the usual finding, but often plasma LDL is also increased, whereas plasma HDL is reduced. **Summary of important causes of secondary hyperlipidaemia** **Predominant hypercholesterolaemia** **Predominant hypertriglyceridaemia** ------------------------------------------------------------------------ -------------------------------------------------------------------------------------------------------------------------------------- Hypothyroidism Alcohol excess Nephrotic syndrome Obesity Cholestasis, e.g. primary biliary cirrhosis Diabetes mellitus and metabolic syndrome Acute intermittent porphyria Chronic kidney disease Anorexia nervosa/bulimia von Gierke's type disease (Type I GSD) Certain drugs or toxins, e.g. ciclosporin and chlorinated hydrocarbons Certain drugs, e.g. estrogens, β-blockers, thiazide diuretics, acitretin, protease inhibitors, some neuroleptics and glucocorticoids Systemic lupus erythematosus Paraproteinaemia **CLASSIFICATION OF HYPOLIPIDAEMIAS** 1. Primary hypolipidaemia 2. Secondary hypolipidaemia **[Primary hypolipidaemias/hypolipoproteinaemias]** Three rare familial diseases require brief mention. 1\. Tangier's disease is due to an **increased rate of apoA‐I catabolism (**Lack of lipidation of apoA1 due to mutation in ABC A1 transporter**)**. Only traces of HDL are detectable in plasma, and plasma LDL-C is also reduced. Cholesterol esters accumulate in the lymphoreticular system, probably due to excessive phagocytosis of the abnormal chylomicrons and  VLDL remnants that result from the apoA‐I deficiency. 2\. Abetalipoproteinaemia is associated with a **complete absence of apoB**. The lipoproteins that normally contain apoB in significant amounts (i.e. chylomicrons, VLDL, IDL and LDL) are absent from plasma. Plasma cholesterol and triglycerides are very low. 3\. Hypobetalipoproteinaemia is due to **decreased synthesis of apoB**. Plasma VLDL and LDL, although reduced, are not absent. **Other [Primary hypolipidaemias/]**hypolipoproteinaemias Inherited disorders of low plasma HDL concentration (**hypoalphalipoproteinaemia**) occur, and plasma HDL-C concentration should ideally be more than 1.0 mmol/L. A number of such conditions have been described (such as **apoA1 deficiency**), many of which are associated with premature cardiovascular disease. In **Tangier's disease**, individuals have very low levels of HDL, large, yellow tonsils, hepatomegaly and accumulation of cholesterol esters in the reticuloendothelial system. There is a defect in the ABC1 gene involved in HDL transport. The causes of a low plasma HDL-C concentration are shown below. **Causes of low plasma high-density lipoprotein (HDL) cholesterol** **Primary** 1. Familial hypoalphalipoproteinaemia 2. ApoA1 abnormalities 3. Tangier's disease 4. Lecithin--cholesterol acyltransferase (LCAT) deficiency 5. Fish-eye disease **Secondary** 1. Smoking 2. Obesity 3. Poorly controlled diabetes mellitus 4. Insulin resistance and metabolic syndrome 5. Chronic kidney disease 6. Certain drugs, e.g. testosterone, probucol, β-blockers (without intrinsic sympathomimetic activity), progestogens, anabolic steroids, bexarotene Defects of apoB metabolism have also been described. In **abetalipoproteinaemia or LDL deficiency** there is impaired chylomicron and VLDL synthesis. This results in a failure of lipid transport from the liver and intestine. Transport of fat-soluble vitamins is impaired and steatorrhoea, progressive ataxia, retinitis pigmentosa and acanthocytosis (abnormal erthyrocyte shape) can result. In **hypobetalipoproteinaemia**, a less severe syndrome occurs, sometimes due to a truncated form of apoB. In **LCAT deficiency**, the accumulation of free unesterified cholesterol in the tissues results in corneal opacities, renal damage, premature atherosclerosis and haemolytic anaemia. The enzyme LCAT catalyses the esterification of free cholesterol. Another condition that is probably due to a defect of LCAT is **fish-eye disease**, in which there may be low HDL cholesterol concentrations and eye abnormalities. **[Secondary hypolipidaemias]:** Rare, causes include 1. Drugs e.g., lipid lowering drugs, etc 2. Malnutrition 3. Malabsorption 4. Hyperthyroidism 5. Liver disorders 6. Wasting diseases 7. Some cancers **CORONARY ARTERY DISEASE AND PREVENTION:** **THE IMPORTANCE OF LIPID LOWERING** Coronary artery disease remains one of the major causes of morbidity and mortality in the industrial world. Traditionally, the major risk factors are hyperlipidaemia, hypertension and smoking, to which can be added diabetes mellitus, a family history of premature coronary heart disease and obesity. With primary (the prevention of the occurrence) and secondary (the prevention of further occurrences) coronary heart disease prevention in mind, the usual strategy adopted is to try to reduce the modifiable risk factors. Cardiovascular risk factors tend to cluster together in individuals and interact in such a way that the overall combined effect is greater than the combined risk of individual factors. **CALCULATION OF CARDIOVASCULAR RISK AND ITS TREATMENT BY LIPID LOWERING** It is possible to lower plasma LDL-C by dietary and other lifestyle means, but the most effective therapy, usually leading to reductions of up to 30% or more, is with HMG‐CoA reductase inhibitors ('statins'). It is this class of drug that has mainly been used in the clinical trials mentioned here. It is conventional to consider cardiovascular risk reduction under the subdivisions of 'secondary prevention' (where the patient has established vascular disease, and the goal is to prevent recurrence), and 'primary prevention' (where the patient has no overt vascular disease, and the goal is to prevent its development). Multiple sets of guidelines have been published, differing to a greater or lesser extent in detail. However, the precise thresholds and targets for treatment continue to evolve, and are partly influenced by economic issues. Guidelines continue to be produced as further clinical trials are published, and vary slightly in different countries. Cholesterol reduction by about 25% reduces all‐cause mortality by 30% and cardiac events by over 40%. Lifestyle interventions to discontinue smoking, adopt a healthy diet and take exercise are important, but should not delay lipid‐lowering therapy. Guidelines suggest that virtually all patients with established vascular disease should be treated with lipid‐lowering drugs, irrespective of baseline cholesterol levels. The goal is to achieve a cholesterol \< 5mmol/L or an LDL-C \< 3mmol/L and if this is not achieved more potent statins or higher doses should be used. In primary prevention, clinical trials have shown that cholesterol lowering (by an average 20%) in hyperlipidaemic men can reduce cardiovascular death and non-fatal MI by about 30%. The available evidence strongly supports the concept that those who will benefit most from treatment are those at greatest overall absolute risk. Someone with multiple modestly elevated risk factors may be at a greater risk than someone with a single markedly elevated risk factor. This means that there is a need for a means of calculating overall risk. The guidelines achieve this by the use of computer‐based risk calculators or charts that stratify risk on the basis of sex, age, smoking, blood pressure and the cholesterol:HDL-C ratio. An important caution is that these calculations do not apply to patients with inherited dyslipidaemias. Guidelines then specify the level of calculated risk that justifies treatment with cholesterol‐lowering drugs. Guidelines disagree on whether there is a cholesterol target in primary prevention similar to that in secondary prevention, or whether the aim is simply to ensure that all eligible patients are treated. **[INVESTIGATION OF PLASMA LIPID ABNORMALITIES]** Plasma sample (**LiH** or EDTA bottle) OR serum sample (**Plain** bottle) after overnight fast (fasting not essential for cholesterol, but is for TG), taken without excessive venostasis, preferably on a normal diet, no alcohol, no recent change in exercise/weight/diet, no recent illness/injury. Be aware that recent acute myocardial infarction or other events evoking an acute phase response (within the preceding 6 weeks) causes falsely low cholesterol levels. Be aware that biological variability of cholesterol is 5-10% and of triglyceride is about 25% (more if non-fasting). Diagnosis and management should therefore preferably be based on repeat measurements 2 weeks apart. 1\. Standing test (Observation of specimen): Hyperlipidaemic blood left to settle for 4 hours without centrifugation, the lipids separated into the top fractions especially in chylomicron syndrome or hypertriglyceridaemia. 2\. Lipid profile (TC, TG, HDL-C, LDL-C): Total cholesterol and triglyceride are measured enzymatically. HDL cholesterol is measured enzymatically after all non-HDL lipoproteins are immunologically rendered non-reactive. LDL-C is calculated using Friedewald\'s formula: LDL-C = total cholesterol - HDL-C - TG/2.2 (Not valid if TG \> 4.5 mmol/l) The Friedewald equation assumes the absence of chylomicrons since the sample was taken in the fasting state, and therefore the total cholesterol is distributed between LDL, HDL and VLDL. The molar ratio of triglyceride to cholesterol in VDL is 2.2, as long as the triglyceride concentration is \ 4.5 mmol/L, and has not been validated in patients on lipid‐lowering drugs. However, it is convenient and cheap. LDL-C is predictive of cardiovascular risk, and strategies that reduce LDL-C provide cardiovascular benefit. Many guidelines for cardiovascular risk reduction recommend LDL-C levels as thresholds or targets for treatment. - Non-HDL cholesterol = TC -- HDL-C The aim of lipid measurements is usually to enable an assessment of cardiovascular risk, and it would be useful to have a simpler approach to testing that avoids the need for fasting, that requires no assumptions about the lipoprotein species present in the sample, and which is valid whether the patient is taking lipid‐lowering drugs or not. Non‐HDL-C is a candidate; this is simply the difference between total cholesterol and HDL-C. It avoids the problems with the Friedewald equation and incorporates all the atherogenic lipoproteins, including LDL, IDL, VLDL, remnant particles and Lp(a). Its predictive value is at least as good in the non‐fasting state as after an overnight fast. Triglyceride levels are increased in people who are obese or who have type 2 diabetes, and non‐HDL-C includes the contributions of these atherogenic triglyceride‐containing lipoproteins. 3\. Apolipoprotein measurement: Apo A, apo B and Lp(a) are measured by protein measuring technique (RIA, nephelometry, or turbidimetry) 4\. Lipid Ratios: a. Total cholesterol: HDL-C ratio, which correlates well with cardiovascular risk b. Apo B: Apo A ratio 5\. Specialised investigations: Enzyme studies and molecular genetic studies, may occasionally be helpful. Plasma lipoprotein lipase and apoC2 (its activator) assays may be useful in chylomicron syndrome, and LDL receptor DNA studies for familial hypercholesterolaemia. ApoE genotype is useful in the diagnosis of type III hyperlipoproteinaemia. 6\. Investigate secondary causes (Other tests): Plasma glucose (DM), Thyroid function tests (Thyroid disorders), Liver function tests (Cholestasis), Renal function test (CKD), Urine ACR (CKD), Urine protein and albumin (Nephrotic syndrome), porphyrins, etc. [Desirable values (by consensus of EAS, ESC and EFLM)] NB: Numerous studies have shown that the incidence of coronary heart disease is directly correlated with plasma cholesterol, even within the 'reference interval'. There is no clear cut‐off between values for normal risk and increased risk, although risk rises particularly rapidly above about 6.5 mmol/L. Because of this association, it is inappropriate to employ reference intervals for plasma cholesterol concentration in the usual way, as these imply health without increased risk of disease. Instead, it seems more appropriate to define a desirable concentration (e.g. \1.3 mmol/L (women) 3. **LDL cholesterol** \