Clinical Chemistry of Diabetes Mellitus PDF

Clinical Chemistry Hyperglycemia & Diabetesmellitus, Hypoglycemia. Disorders of lipid metabolism Dr.Ahmed Zakaria 1  Hyperglycemia and diabetes mellitus oHYPERGLYCEMIA may be due to: - Intravenous infusion of...

Clinical Chemistry Hyperglycemia & Diabetesmellitus, Hypoglycemia. Disorders of lipid metabolism Dr.Ahmed Zakaria 1  Hyperglycemia and diabetes mellitus oHYPERGLYCEMIA may be due to: - Intravenous infusion of glucose-containing fluids - Sever stress (transient effect) such as trauma, myocardial infarction or cerbrovascular accidents. - Diabetes mellitus or impaired glucose regulation. 2  Diabetes Mellitus oDM is caused by an absolute or relative insulin deficiency. oIt has been defined by WHO, on the basis of laboratory findings: - fasting venous plasma glucose concentration of 7.0 mmol/l or more (more than one occasion in the presence of diabetes symptoms) - OR a random venous plasma glucose concentration of 11.1 mmol/l or more. ❖ Sometime an oral glucose tolerance test (OGTT) may be required to establish the diagnosis. 3  Classification of DM I. Type 1 diabetes mellitus (insulin-dependent diabetes mellitus) - Cause: Destruction of beta cells of pancreatic islets - Consequence: Absolute deficit of insulin - Present during childhood and adolescence - Insulin therapy is essential A- subtype: induced by autoimmunity processes. B- subtype: idiopathic diabetes mellitus. There is also LADA (Latent autoimmune diabetes of adults), sometime called slow-onset type 1 diabetes 4  Classification of DM II. Type 2 diabetes mellitus (non insulin-dependent diabetes mellitus) - The disorder ranging from mainly insulin resistance with relative insulin deficiency to a predominantly secretory defect with insulin resistance. - Insulin may sometimes be needed - Onset is most usual during adult life - There is familial tendency and an associated with obesity. 5 III. Other specific types of diabetes mellitus An inherited disorders, either by reducing insulin secretion OR by causing relative insulin deficiency because of resistance to its action or of insulin receptor defects, despite high plasma insulin concentration. Genetic defect of beta-cell function ❑Maturity-onset diabetes of the young (MODY): 1. MODY 1: mutation of hepatocyte nuclear factor (HNF4A) gene 2. MODY 2: mutation of glucokinase gene 3. MODY 3: mutation of HNF1A gene Some cases are thought to be point mutation in mitochondrial DNA associated with DM and deafness 6 III. Other specific types of diabetes mellitus Genetic defect of insulin action Type A insulin resistance (insulin receptor defect), for example leprechaunism, lipoatrophy and Rabson-Mendenhall syndrome Insulin deficiency due to pancreatic disease 1- Chronic pancreatitis 2- Pancreatectomy 3- Haemochromatosis 4- Cystic fibrosis 7 III. Other specific types of diabetes mellitus Endocrinopathies Relative insulin deficiency, due to excessive GH (acromegaly), phaeochromocytoma, glucocorticoid secretion (Cushing’s syndrome) Drugs 1- Thiazide diuretics 2- Interferon alpha 3- Glucocorticoids Infections 1- Septicaemia 2- Congenital rubella 3- Cytomegalovirus 8 III. Other specific types of diabetes mellitus Rare form of autoimmune-mediated diabetes 1- Anti-insulin receptor antibodies 2- Stiff man syndrome, with high level of GAD autoantibodies Genetic syndrome associated with diabetes 1- Down’s syndrome 2- Turner’s syndrome 3- Klinefelter’s syndrome 4- Myotonic dystrophy 9  IV. Gestational diabetes mellitus oWomen at high risk for GDM including: previously given birth to a high-birth weight baby, obese, family history of DM, high-risk ethnic groups (Black or South Asian). oScreening at the earliest opportunity and, if normal, retested at about 24-28 weeks, as glucose tolerance progressively deteriorates throughout pregnancy. oFasting venous plasma glucose ≥ 7.0 mmol/l and/or random measurement ≥ 11.1 mmol/l. oSix weeks post partum, the woman should reclassified with repeat OGTT 10  ❖ Impaired glucose tolerance (IGT) oFasting venous plasma glucose concentration < 7.0 mmol/l o2 h after an oral glucose intake (OGTT), plasma glucose between 7.8 mmol/l and 11.1 mmol/l o Some patients with IGT develop diabetes mellitus later oPregnancy IGT is treated as GDM because of the risks to the fetus. 11 ❖ Impaired fasting glucose (IFG) oLike IGT, refers to a metabolic stage intermediate between normal glucose homeostasis and DM. oFasting venous plasma glucose ≥ 6.1 mmol/l but < 7 mmol/l, and < 7.8 mmol/l 2h after an oral glucose intake (OGTT) 12  ❖ Insulin resistance syndrome or metabolic syndrome oThere is an aggregation of lipid and non-lipid risk factors of metabolic origin. oA particular cluster is Known metabolic syndrome, syndrome X OR Reaven’s syndrome and is closely linked to insulin resistance. oDefined by the presence of three or more of the following features: Abnormal obesity (west circumference): - Male > 102 cm (40 in) - Female > 88 cm (35 in) 13  ❖ Insulin resistance syndrome or metabolic syndrome Fasting plasma TG > 1.7 mmol/l Fasting plasma HDL-cholesterol: - Male < 1.0 mmol/l - Female < 1.3 mmol/l blood pressure ≥ to 130/85 mm Hg Fasting blood glucose > 5.5 mmol/l Other associated features may include PCOS, fatty liver, raised fibrinogen and plasminogen activator inhibitor 1 concentrations, renal sodium retention, hyperuricaemia and dense LDL particles 14  Metabolic features of DM ❖Hyperglycemia oIf plasma glucose > 10.0 mmol/l, glycosuria would be expected High urinary glucose concentration produce osmotic diuresis and therefore polyuria. Cerebral cellular dehydration due to hyperosmolality, secondary to hyperglycemia, causes polydepsia Prolonged osmotic diuresis may cause excessive urinary electrolyte loss. 15  Metabolic features of DM ❖Abnormal in lipid metabolism These may be secondary to insulin deficiency Lipolysis is enhanced and plasma NEFA concentration rise. In the liver NEFA converted to acetyl CoA and ketones or re- esterified to form TG and incorporated into VLDL which accumulate in plasma because lipoprotein lipase, which require insulin for optimal activity to catabolise VLDL HDL-cholesterol tend to be low in type 2 DM 16  Metabolic features of DM Chylomicronaemia may also occur if insulin deficiency is very sever Cholesterol synthesis increased with an associated increase in LDL ❑ As a consequent, patients with DM may show high TG, raised cholesterol and low HDL-cholesterol 17  Long-term effects of DM Vascular disease is a common complication of DM ❑ Macrovascular disease due to abnormalities of large vessels (coronary artery, cerebrovascular or peripheral vascular insufficiency). ▪ The condition probably related to alteration of lipid metabolism and associated hypertension. ❑ Microvascular disease due to abnormalities of small blood vessels particularly affects the retina (diabetic retinopathy) and the kidney (nephropathy). ▪ May be related to inadequate glucose control. 18 Long-term effects of DM Characteristic lesion: The renal complications may be partly due to the increase glycation of structural proteins in the arterial walls supplying the glomerular basement membrane; similar vascular changes in the retina may account for the incidence of diabetic retinopathy. ❑ Infections are also more common in diabetic patients, e.g. urinary tract or chest infections 19  Long-term effects of DM ❑Diabetic neuropathy can occur ❑ Diabetic ulcer, e.g. of the feet, can lead gangrene and amputation. ❑ The joints can also affected ❑ Skin disorder; e.g. abscesses 20 Monitoring of DM ❖Glycosuria ✓Defined as a concentration of urinary glucose detectable. ✓Usually, the proximal tubular cells reabsorb most of the glucose in the glomerular filtrate. ✓Glycosuria occur when the plasma, and therefore glomerular filtrate, concentrations exceed the tubular reabsorptive capacity. ✓When plasma glucose concentration > 10.0 mmol/l 21  Monitoring of DM ❖Blood glucose ❖Glycated haemoglobin HbA1c is formed by non-enzymatic glycation of haemoglobin and is dependent on: 1- mean plasma glucose concentration 2- lifespan of the red cell ✓Falsely low values may be found in patients with haemolytic disease. ✓HbA1c gives a retrospective assessment of the mean plasma glucose concentration during the preceding 6-8 weeks 22  Monitoring of DM ✓The higher HbA1c, the poorer the mean diabetic or glycaemic control. ❖Fructosamine ✓Plasma fructosamine may be used to assess glucose control over a shorter time course than that of HbA1c (about 2-4 weeks). ✓Fructosamine reflect glucose bound to albumin, which has a plasma half-life of about 20 days but is problematic in patients with hypoalbuminaemia. 23  Monitoring of DM ❖Blood ketones ❖Urinary albumin determination and diabetic nephropathy ✓One of the earliest signs of diabetic renal dysfunction is the development of small amounts of albumin in the urine (microalbuminuria). ▪ Normoalbuminuria < 30 mg/day or < 20 µg/min. ▪ Microalbuminuria 30-300 mg/day or 20-200 µg/min. oUntreated microalbuminuria can progress to albuminuria (> 300 mg/day), impaired renal function and finally end-stage renal failure. 24  Monitoring of DM ✓A random urine sample or timed overnight collection can be useful to assess urinary albumin excretion, although the standard test is the urinary albumin to creatinine ratio (ACR), which avoids a timed urine collection. ACR < 2.5 g/mol for male ACR < 3.5 g/mol for female 25  Acute metabolic complication of DM ❖Hypoglycemia ▪ This is probably the most common cause of coma seen in diabetic patients ▪ Hypoglycemia is most commonly caused by overadministration of insulin plus inadequate food intake, or taken excessive exercise. ▪ Overadministration of hypoglycemic medicine 26  Acute metabolic complication of DM ❖Diabetic ketoacidosis Insulin insufficiency triggers the following: ▪ Increase lipid and protein breakdown ▪ Enhanced hepatic gluconeogenesis and impaired glucose entry into cells The clinical consequences of diabetic ketoacidosis are due to: Hyperglycemia causing plasma hyperosmolality Metabolic acidosis Glycosuria 27  Acute metabolic complication of DM ❖Diabetic ketoacidosis 1. Vomiting water & electrolyte loss (increase fluid depletion)(extracellular depletion) shift of water out of the cellular compartment and sever cellular dehydration 2. Haemoconcentration & glomerular filtration rate cause uraemia due to renal circulatory insufficiency 3. The rate of hydrogen ions production exceeds the rate of bicarbonate generation, which buffer H+, lead to plasma bicarbonate falls. H+ secretion causes a fall in urinary pH. 28  Acute metabolic complication of DM ❖Diabetic ketoacidosis 4. Failure of glucose entry into cells & glomerular filtration rate may raise plasma potassium concentration, before treatment is started. 29  Acute metabolic complication of DM ❖Hyperosmolal non-ketotic coma (HONK) (hyperosmolar hyperglycaemic state (HHS)) ▪ Insulin is present to some degree : it suppress fat breakdown lack of ketosis ▪ insulin is present to some degree : its effective is less than needed for effective glucose transport hyperglycemia glycosuria & polyuria body fluid depletion intracellular dehydration, which contribute to coma ▪ Hypernatraemia due to predominant water loss is more commonly found than in ketoacidosis. 30  Acute metabolic complication of DM ❖Lactic acidosis Can cause a high anion gap metabolic acidosis and coma ❖Other causes of coma in patients with DM - Cerbrovascular accident because of the increased incidence of vascular disease - Diabetic patients can have any other coma, e.g. drug overdose - Diabetic patients are also more at risk of diabetic nephropathy & renal failure & thus uraemia coma 31  Investigation of suspected diabetes mellitus Fasting or random blood glucose determinations. OGTT may be required Plasma glucose estimation if a patient presents with symptoms of DM or glycosuria or if there is strong family history. DM is confirmed if one of the following is present: ✓A fasting (at least 10 h) venous plasma concentration ≥ 7.0 mmol/l on two occasions or once with symptoms. ✓A random venous plasma concentration ≥ 11.1 mmol/l on two occasions or once with symptoms. 32  Investigation of suspected diabetes mellitus DM is unlikely if the fasting venous plasma glucose concentration < 5.5 mmol/l on two occasions. Random plasma glucose is less reliable for excluding than for confirming the diagnosis. Indication for performing an OGTT to diagnose DM: ✓Fasting venous plasma glucose concentration between 5.5 mmol/l and < 7.0 mmol/l, although this debatable as WHO recommends an OGTT if FPG> 6.0 mmol/l. ✓Random venous plasma glucose between 7.0 mmol/l and < 11.1 mmol/l. ✓A high index of clinical suspicion of DM, such as a patient at high risk of GDM with equivocal blood glucose results. 33  Investigation of suspected diabetes mellitus Factors may affect the result of OGTT: ✓Previous diet: no special restriction if patient on normal diet for 3- 4 days, while after a period of carbohydrate restriction, e.g. weight reducing diet may cause abnormal glucose tolerance because probably metabolism is adjusted to a “fasted state” and favours gluconeogenesis. ✓Time of day: most OGTTs are performed in the morning and the reference values are quoted for this time of day. There is evidence that afternoon results yield higher plasma glucose concentration. This may be due to circadian variation in islet cell responsiveness. ✓Drug steroid, oral contraceptives AND thiazide diuretics may impair glucose tolerance. 34 Investigation of suspected diabetes mellitus HbA1c > 6.5 % is diagnostic of DM, but this is not universally agreed as other factors, e.g. haemoglobin variants and erythrocyte lifespan may affect HbA1c levels. 35  Hypoglycaemia Define if plasma glucose is less than 2.5 mmol/l in a specimen collected into a tube containing an inhibitor of glycolysis, e.g. fluoride oxalate. Blood cells continue to metabolize glucose in vitro if specimen collected without such an inhibitor (the result of glucose concentration in whole blood will be approximately 1.0 mmol/l lower) Symptoms: sweeting, tachycardia, agitation, faintness, and dizziness or lethargy may progress rapidly to coma and if untreated, permanent cerebral damage or death may occur. 36 ❑Hypoglycemia divided into: ✓Hypoinsulinaemia hypoglycaemia ✓Hyperinsulinaemia hypoglycemia ✓Reactive (functional) hypoglycaemia ❖Hypoinsulinaemia hypoglycaemia Non-pancreatic tumours (non-islet cell tumours) ✓Carcinomas (especially of the liver) and sarcomas have been reported to cause hypoglycaemia, commonly associated with retroperitoneal tumours of mesenchymal origin, but also with lymphomas, haemangiopercytomas, liver carcinoma and leukaemia. 37 ✓The mechanism is not clear but may sometimes be due to the secretion of insulin-like growth factor 2 (IGF-2) or abnormal glycosylated big IGF-2. Endocrine causes ✓Hypoglycaemia may occur in hypothyroidism, pituitary or adrenal insufficiency. Impaired liver function ✓Hypoglycaemia is a rare complication of liver disease, despite its (liver) central role in the maintenance of plasma glucose concentration. It can be seen in very sever liver disease as the whole liver is affected. Renal failure ✓Renal failure can result in hypoglycaemia as the kidney, like the liver, gluconeogenic organ. 38 ❖Hyperinsulinaemia hypoglycaemia Insulin or other drugs are probably the most common causes. Hypoglycaemia in diabetic patient may be caused by accidental insulin overdosage, by changing insulin requirement or by failure to eat after insulin has been given. Hypoglycaemia due to exogenous insulin suppresses insulin and c- peptide secretion. Measurement of plasma c-peptide concentrations may help to differentiate exogenous insulin administration from endogenous insulin secretion, whether it is from insulinoma or following pancreatic stimulation by sulphonylurea drugs. 39 ✓An insulinoma is usually a small, it is benign primary tumour of the islet cells of the pancreas. Multiple tumours may occur and may be part of the syndrome of multiple endocrine neoplasia (MEN). As with other functioning endocrine tumours, hormone secretion is inappropriate and usually excessive. In response to exogenous insulin, insulin antibody can form. Sometimes, insulin antibodies form despite the patient never having been exposed to exogenous insulin- autoimmune insulin syndrome (AIS). Insulin receptor antibodies may cause hypoglycaemia, although they sometimes lead to insulin resistance and hyperglycaemia. 40 ❖Reactive functional hypoglycaemia ✓Some people develop symptomatic hypoglycaemia after 2 and 4 h of meal or a glucose load. ✓Following a gastrectomy or bariatric gastric banding, when rapid passage of glucose into the intestine, and rapid absorption, and may stimulate excessive insulin secretion. Alcohol-induced hypoglycaemia ✓Hypoglycaemia may develop between 2 -10 h after ingestion of large amounts of alcohol. ✓Hypoglycaemia is probably caused by suppression of gluconeogenesis during the metabolism of alcohol. 41 Investigation of adult hypoglycaemia 42 Lipoprotein metabolism The lipoprotein system evolved to solve the problem of transporting fats around the body in the aqueous environment of the plasma. A lipoprotein is a complex spherical structure that has a hydrophobic core wrapped in a hydrophilic coating The core contains triglyceride and cholesteryl esters, while the surface contains phospholipid, free cholesterol and proteins – the apolipoproteins. Cholesterol is an essential component of all cell membranes and is a precursor for steroid hormone and bile acid biosynthesis. Triglyceride is central to the storage and transport of energy within the body Lipoprotein metabolism can be thought of as two cycles, one exogenous and one endogenous, both centred on the liver. These cycles are interconnected. Two key enzyme systems are involved in lipoprotein metabolism, i.e.: Lipoprotein lipase (LPL) releases free fatty acids and glycerol from chylomicrons and VLDL into the tissues. Lecithin: cholesterol acyl transferase (LCAT) forms cholesteryl esters from free cholesterol and fatty acids.  The exogenous lipid cycle Dietary lipid is absorbed in the small intestine and incorporated into chylomicrons that are secreted into the lymphatics and reach the bloodstream via the thoracic duct. In the circulation, triglyceride is gradually removed from these lipoproteins by the action of lipoprotein lipase. This enzyme is present in the capillaries of a number of tissues, predominantly adipose tissue and skeletal muscle As it loses triglyceride, the chylomicron becomes smaller and deflated, with folds of redundant surface material. These remnants are removed by the liver. The cholesterol may be utilized by the liver to form cell membrane components or bile acids, or may be excreted in the bile. The liver provides the only route by which cholesterol leaves the body in significant amounts.  The endogenous lipid cycle The liver synthesizes VLDL particles that undergo the same form of delipidation as chylomicrons by the action of lipoprotein lipase. This results in the formation of an intermediate density lipoprotein (IDL), which becomes low density lipoprotein (LDL) when further delipidated. LDL may be removed from the circulation by the high affinity LDL receptor or by other scavenger routes that are though to be important at high LDL levels and the main way in which cholesterol is incorported into atheromatous plaques  HDL particles are derived from both liver and gut. They act as cholesteryl ester shuttles, removing the sterol from the peripheral tissues and returning it to the liver. The HDL is taken up either directly by the liver, or indirectly by being transferred to other circulating lipoproteins, which then return it to the liver. This process is thought to be anti-atherogenic, and an elevated HDLcholesterol level has been shown to confer a decreased risk of coronary heart disease on an individual. Clinical disorders of lipid metabolism Lipoprotein disorders are some of the commonest metabolic diseases seen in clinical practice. They may present with their various sequelae which include: coronary heart disease (CHD) acute pancreatitis failure to thrive and weakness Cataracts Classification Currently there is no satisfactory comprehensive classification of lipoprotein disorders. Genetic classifications have been attempted but are becoming increasingly complex as different mutation are discovered Familial hypercholesterolaemia (FH), which may present with xanthelasma (Fig 67.1), tendon xanthomas, severe hypercholesterolaemia and premature coronary heart disease, may be due to any of over 500 different mutations of the LDL receptor gene. Mutations of the apolipoprotein (apo) B gene can give an identical syndrome. Familial hyperchylomicronaemia, which presents with recurrent abdominal pain and pancreatitis, may result from genetic mutations of the lipoprotein lipase or apo C-II genes. Eruptive xanthomas (Fig 67.2) are characteristic of hypertriglyceridaemia.  Until gene therapy and/or specific substitution therapy become more widely available, genetic classifications, while biologically illuminating, are unlikely to prove very useful in practice. In practice, lipoprotein disorders are simplistically classified as being: Primary – when the disorder is not due to an identifiable underlying disease. Secondary – when the disorder is a manifestation of some other disease. Primary The Fredrickson or World Health Organization classification is the most widely accepted for the primary hyperlipidaemia (Fig 67.3). It relies on the finding of plasma analysis, rather than genetics. As a result, patients with the same genetic defect may fall into different groups, or may change grouping as the disease progresses or is treated (Table 67.1). The major advantage of this classification is that it is widely accepted and gives some guidance for treatment. The six types of hyperlipoproteinaemia defined in the Fredrickson classification are not equally common. Types I and V are rare, while types IIa, IIb and IV are very common. Type III hyperlipoproteinaemia, also known as familial dysbetalipoproteinaemia, is intermediate in frequency, occurring in about 1/5000 of the population. Secondary Secondary hyperlipidaemia is a wellrecognized feature of a number of diseases (Table 67.2) that divide broadly into two categories: Clinically obvious diseases such as renal failure, nephrotic syndrome and cirrhosis of the liver Covert conditions that may present as hyperlipidaemia. These include hypothyroidism, diabetes mellitus and alcohol abuse. Atherogenic profiles The causal association of certain forms of hyperlipidaemia and CHD is clearly the major stimulus for the measurement of plasma lipids and lipoproteins in clinical practice. The most common lipid disorder linked with atherogenesis and an increased risk of CHD is an elevated plasma LDL cholesterol level, but increasingly it is being recognized that individuals with low plasma HDL cholesterol and hypertriglyceridaemia are also at increased risk