BIOT221 Western Diagnostic Techniques

Transcription

1 BIOT221 Western Diagnostic Techniques Session 4 Blood Based Pathology Vitamins, Minerals & Glucose Bioscience Dept Endeavour College of Natural Health endeavour.edu.au 1

2 SESSION OBJECTIVES Understand the clinical relevance and application of the following tests: Serum Magnesium Vitamin (B 12 ) Red Cell Folate Fasting Serum Glucose Glucose Tolerance Test (GTT) HbA1C Endeavour College of Natural Health endeavour.edu.au 2

3 Serum Magnesium (Mg) Magnesium is the major intracellular cation and is involved in almost every metabolic and neuromuscular function in the body. This test is used to identify magnesium deficiency or overload. Components: (Adult Values) Magnesium meq/l Critical Values: o <1 or >9 meq/l Endeavour College of Natural Health endeavour.edu.au 3

4 SERUM MINERALS - MG 2+ - INTRODUCTION Mg 2+ is a primary intracellular cation (second most abundant, 60% found in bone), that is involved in the phosphorylation of ATP for energy production. Mg 2+ concentration is determined by intestinal absorption, renal excretion, and exchange with bone and intracellular fluid. By regulating enzymes and controlling intracellular calcium, Mg 2+ affects smooth muscle function and vasoconstriction, hence its critical role in cardiovascular function. In extracellular fluid, it influences neuromuscular response, hence its role as a supplement to reduce muscular tension. Endeavour College of Natural Health endeavour.edu.au 4

5 Interpreting the Results HIGH Dehydration Renal insufficiency Addisons disease Ingestion of magnesium-containing antacids Ingestion of magnesium salts Hypothyroidism LOW Malnutrition Diarrhoea Malabsorption Hypoparathyroidism Alcoholism Chronic renal tubular disease Diabetic acidosis Critical High - >9mEq/L Retardation of neuromuscular conduction Slowing of cardiac conduction Respiratory depression Lethargy Nausea & vomiting Slurred speech Critical Low - <1mEq/L Cardiac irritability and arrhythmia Muscular weakness Mental irritability and delirium convulsions Endeavour College of Natural Health endeavour.edu.au 5

6 SERUM MINERALS - MG 2+ - INTERFERING/RISK FACTORS Haemolysis of the collected blood sample should be considered in patients with a significantly elevated serum magnesium, who are otherwise asymptomatic. Drugs that increase Mg 2+ levels include thyroid medication, antacids, laxatives, calcium-containing medication, lithium, loop diuretics, and aminoglycoside antibiotics. Drugs that decrease Mg 2+ levels include diuretics, some antibiotics and insulin. Endeavour College of Natural Health endeavour.edu.au 6

7 Vitamin B 12 - Cyanocobalamin A measure of the amount of vitamin B 12 in the blood, which is used to investigate the underlying cause for megaloblastic anaemia Components: (Adult Values) Vitamin B pmol/l Endeavour College of Natural Health endeavour.edu.au 7

8 VITAMIN B 12 CYANOCOBALAMIN Vitamin B 12 is necessary for conversion of the inactive form of folate to the active form. This reaction is vital for the synthesis of nucleic acids and amino acids. This is most notable in the formation and function of RBCs, where deficiency has a direct effect on the cell morphology (megaloblastic anaemia) May take 6-18 months of Vitamin B 12 depletion before anemia develops. Serum B12 is a measurement of recent B 12 ingestion and poorly correlates to long term deficiency. Prolonged B 12 deficiency is more accurately measured by urinary methylmalonic acid (MMA) B 12 converts MMA-CoA to succinyl CoA Meat, eggs, and diary products are the main source of Vitamin B 12. Some sea greens and fermented also contain B 12 Endeavour College of Natural Health endeavour.edu.au 8

9 VITAMIN B 12 CYANOCOBALAMIN In the stomach, gastric acid detaches Vit B 12 from its binding proteins. Intrinsic factor (IF), produced in the gastric mucosa (parietal cells), then attaches to B 12 and carries it to the ileum where absorption occurs. Generally without IF, Vit B 12 cannot be absorbed. Recent research has shown that a small amount (1-2%) of ingested B 12 may be passively absorbed. However this would be unlikely to correct a frank B 12 deficiency. Deficiency of IF is the most common cause of Vit B 12 deficiency (perinicous anemia). Often associated with autoimmune parietal cell destruction. Lack of gastric acid to separate the ingested Vit B 12 from its binding proteins also gives rise to deficiency, as IF cannot bind with B 12 until the binding protein has been removed Malabsorption can be caused by diseases of the small terminal ileum such as IBD and Crohns disease or resection. Endeavour College of Natural Health endeavour.edu.au 9

10 Interpreting the Results HIGH Leukemia Polycythemia vera Severe liver dysfunction Myeloproliferative disease (false elevation due to transcobalamin) LOW Pernicious anaemia Malabsorption (IBD, Crohn Dx) Intestinal worm infestation Atrophic gastritis Zollinger-Ellison syndrome Proximal gastrectomy Resection of Ileum Achlorhydria Pregnancy Vitamin C deficiency Folic Acid deficiency Endeavour College of Natural Health endeavour.edu.au 10

11 VITAMIN B 12 WHAT DO THE TEST RESULTS MEAN? A patient with B12 deficiency will usually be treated either with oral supplementation or intramuscular (IM) injections. Some sub-lingual (SL) preparations are also available. SL and IM delivery overcomes the need for IF Vitamin B 12 and folate should be measured when a FBC indicates the presence of large red cells (macrocytic cells). When a person, especially an elderly person, exhibits mental or behavioral changes such as irritability, confusion, depression and/or paranoia, vitamin B 12 may be done to help diagnose the underlying cause They may also be used when a patient has physical symptoms that suggest a B 12 deficiency, including dizziness, weakness, fatigue, tingling or numbness in extremities, or a sore mouth or tongue. Endeavour College of Natural Health endeavour.edu.au 11

12 EVALUATING PERNICIOUS ANEMIA Pernicious anemia is the major cause of megaloblastic anemia. It occurs as a result of B12 deficiency which is secondary to an intrinsic factor (IF) deficiency. Intrinsic factor deficiency occurs mostly because of an auto-immune process that either destroys the parietal cells that produce IF, or directly destroys the IF itself. Surgical gastrectomy may also result in IF deficiency. Previously a Schillings Test would be done if pernicious anemia was suspected, however this test is rarely performed now, due to the need to administer radioactive labelled B 12. If pernicious anemia is suspected, anti-parietal cell antibodies and antiintrinsic factor antibodies should be performed to determine autoimmune pernicious anemia. Endeavour College of Natural Health endeavour.edu.au 12

13 Serum Folate & Red Cell Folate This test quantifies the level of folate in the plasma or within the red blood cells. It is used in patients who have megaloblastic anemia and to assess nutritional status, especially in alcoholics and pregnancy care. Components: (Adult Values) mmol/l (as plasma folate) nmol/L (as RCF) Endeavour College of Natural Health endeavour.edu.au 13

14 FOLATE AND RED CELL FOLATE It is tested in patients who have megaloblastic anemia (macrocytic) which results from inhibition of DNA synthesis in red blood cell production. This leads to continuing cell growth without division, which presents as macrocytosis. Folic acid, one of the B vitamins, is necessary for normal function of RBCs and WBCs and for the adequate synthesis of certain purines and pyrimidines, which are the precursors of DNA. It is also used in the synthesis of several amino acids. Folate is also involved in the conversion of homocysteine to methionine for protein synthesis and other functions. Vit B 12 is necessary for conversion of inactive 5-methyltetrahydrofolate to the active tetrahydrofolate, the active form of folate. As with Vit B 12 the folate level depends on adequate dietary ingestion and normal intestinal absorption of this vitamin Folate is also required for neural tube development in the foetus during pregnancy. Folate deficiency in pregnancy is associated with neural tube defects such as spina bifida in infants. Endeavour College of Natural Health endeavour.edu.au 14

15 Interpreting the Results HIGH Pernicious anaemia Vegetarianism / veganism Recent blood transfusion (e.g. following surgery) LOW Malnutrition Malabsorption (e.g. coeliac disease) Pregnancy Megaloblastic anaemia Haemolytic anaemia Malignancy Liver disease Alcoholism Chronic renal disease Endeavour College of Natural Health endeavour.edu.au 15

16 Blood Glucose A direct measurement of the level of glucose in the blood. Commonly performed in the assessment of diabetic patients. It can be performed on a venous sample collected via venesection or as a capillary sample collected by finger prick and analyzed in a glucometer. Components: (Adult Values) mg/dL or <6.1 mmol/l (Fasting) Critical values: <50 or >450mg/dL or <3 or >25 mmol/l Endeavour College of Natural Health endeavour.edu.au 16

17 GLUCOSE - INTRODUCTION Glucose is a simple sugar that serves as the main source of energy for the body The carbohydrates we eat are broken down into glucose (and a few other simple sugars), absorbed by the small intestine and circulated throughout the body Most of the body's cells require glucose for energy production; the brain and nervous system cells rely on glucose for energy, and can only function when glucose levels in the blood remain within a certain range The body's use of glucose depends on the availability of insulin, a hormone produced by the pancreas Insulin acts to control the transport of glucose into the body's cells to be used for energy. It also directs the liver to store excess glucose as glycogen (for short term energy storage) and promotes the synthesis of fats, which form the basis of a longer term store of energy Endeavour College of Natural Health endeavour.edu.au 17

18 GLUCOSE - INTRODUCTION Normally blood glucose levels rise slightly after a meal, and insulin is released to lower them, with the amount of insulin relative to the amount of glucose derived from the meal. If blood glucose levels drop too low, such as might occur in between meals or after a strenuous workout, glucagon (another hormone from the pancreas) is produced to tell the liver to release some of its glycogen stores, raising the blood glucose levels. If the glucose/insulin system is working properly the amount of glucose in the blood remains fairly stable. Hyperglycaemia (high blood glucose) and hypoglycaemia (low blood glucose) can be caused by a variety of conditions. Severe or sudden episodes of high or low blood glucose levels can be life threatening, causing organ failure, brain damage, coma and in extreme cases, death. Long-term high blood glucose levels can lead progressively to insulin resistance and Diabetes, as well as cause damage to body organs such as the kidneys, eyes, blood vessels, heart and nerves. Hyperglycaemia may arise during pregnancy (known as 'gestational diabetes') can cause mothers to give birth to large babies who may have low glucose levels Endeavour College of Natural Health endeavour.edu.au 18

19 GLUCOSE - HOW IS THE TEST USED? The fasting blood glucose level (collected after an 8 to 10 hr fast) is used to screen for and diagnose diabetes An oral glucose tolerance test (OGTT / GTT) may also be used to diagnose diabetes To be certain of a diagnosis two tests (either the fasting glucose or the OGTT) should be done at different times The OGTT involves a fasting glucose measurement, followed by the patient drinking a glucose drink to 'challenge' their system, followed by another glucose test two hours later Gestational diabetes is a temporary type of hyperglycaemia seen in some pregnant women, usually late in their pregnancy Almost all pregnant women are screened for gestational diabetes between their 24th and 28th week of pregnancy using a test for glucose in the urine If glucose is detected in the urine, they are considered at risk of developing gestational diabetes and they will undergo further testing Endeavour College of Natural Health endeavour.edu.au 19

20 Interpreting the Results HIGH Diabetes Mellitus Acute stress response Cushings syndrome Pheochromocytoma Chronic renal failure Glucagonoma Acute pancreatitis Diuretic therapy Corticosteroid therapy Acromegaly LOW Insulinoma Hypothyroidism Hypopituitarism Addisons disease Chronic liver disease Insulin overdose starvation Endeavour College of Natural Health endeavour.edu.au 20

21 Glucose Tolerance Test A measurement of the blood glucose level 1 and 2 hours (up to 5 hours) after ingestion of a measured dose of glucose (50-75mg). This is compared to a baseline fasting sample. Commonly used to diagnose diabetes mellitus. In some cases a 1hr post-prandial Glucose Challenge Test (GCT) may be used in place of the full GTT. Components: (Adult Values) <110mg/dL (6.1mmol/L) Fasting <200mg/dL (11.1mmol/L) 1 hour <140mg/dL (7.8mmol/L) 2 hours Endeavour College of Natural Health endeavour.edu.au 21

22 Interpreting the Results HIGH Diabetes mellitus Gestational diabetes Malnutrition Hyperthyroidism Acute stress response Cushings syndrome Pheochromocytoma Chronic renal failure Glucagonoma Diuretic therapy Corticosteroid therapy Acute pancreatitis Acromegaly Myxeodema LOW Insulinoma Hypothyroidism Hypopituitarism Addisons disease Chronic liver disease Insulin overdose starvation Endeavour College of Natural Health endeavour.edu.au 22

23 INTERPRETING THE RESULTS Source: Mosby s manual of Diagnostic and Laboratory Tests Endeavour College of Natural Health endeavour.edu.au 23

24 GLUCOSE - HOW IS THE TEST USED? Diabetics must monitor their own blood glucose levels, often several times a day, to determine how far above or below normal their glucose is and to determine what oral medications or insulin injections they may need This is usually done by placing a drop of blood from a finger prick onto a plastic indicator strip and then inserting the strip into a glucose meter, a small machine that provides a digital readout of the blood glucose Source: Date accessed 12/01/2010 Endeavour College of Natural Health endeavour.edu.au 24

25 Source: Date accessed 12/01/2010 Endeavour College of Natural Health endeavour.edu.au 25

26 GLUCOSE - WHEN IS IT REQUESTED? The test may be used as part of a routine examination especially in those people at high risk of developing diabetes those with a family history of diabetes those who are overweight those who are more than 45 years old The glucose test may also be used to help diagnose diabetes when someone has symptoms of hyperglycaemia such as: Increased thirst Increased urination Tiredness Blurred vision Slow-healing infections Endeavour College of Natural Health endeavour.edu.au 26

27 GLUCOSE - WHEN IS IT REQUESTED? Glucose may also be tested when a person has symptoms of hypoglycaemia, such as: Sweating Hunger Trembling Anxiety Confusion Blurred Vision Glucose testing is also done in emergency settings to determine if low or high glucose is contributing to symptoms such as fainting and unconsciousness If a patient has impaired glucose tolerance (when the fasting glucose or OGTT levels are higher than normal but not high enough to be diagnosed as a definite diabetic) their doctor will request a glucose at regular intervals to monitor their progress Pregnant women are usually screened for gestational diabetes late in their pregnancies, unless they have symptoms earlier or have had gestational diabetes with a previous child Endeavour College of Natural Health endeavour.edu.au 27

28 GLUCOSE WHAT DOES THE RESULT MEAN? Fasting Blood Glucose Glucose level From 3.6 to 6.0 mmol/l From 6.1 to 6.9 mmol/l Indication normal glucose tolerance impaired fasting glucose 7.0 mmol/l and above probable diabetes Oral Glucose Tolerance Test (ogtt) -75g dose GLUCOSE LEVEL Less than 7.8 mmol/l From 7.8 to 11.0 mmol/l Over 11.1 mmol/l INDICATION normal glucose tolerance impaired glucose tolerance probable diabetes Endeavour College of Natural Health endeavour.edu.au 28

29 GLUCOSE WHAT DOES THE RESULT MEAN? The National Diabetes Data Group (NDDG) has defined criteria sufficient for the diagnosis of diabetes mellitus. Source: Mosby s manual of Diagnostic and Laboratory Tests Endeavour College of Natural Health endeavour.edu.au 29

30 Glycosylated Haemoglobin (HbA 1 C) A measurement of the amount of HbA 1 that has combined (glycosylated) with glucose to form HbA 1 C. The level of HbA1C indicates serum glucose controls over the previous 3-4 month period given the approximately 120 day lifecycle of the RBCs Components: (Adult Values) 4-5.9% - Non-diabetic <7% - Good diabetic control 8-9% - Fair diabetic control >9% - Poor diabetic control Endeavour College of Natural Health endeavour.edu.au 30

31 HBA 1C - INTRODUCTION Approximately 98% of haemoglobin is haemoglobin A, of which approximately 7% is haemoglobin A 1 (HbA1). There are 3 sub-types of HbA 1 A, B and C. Sub-type HbA 1 C combines strongly with glucose through a process known as glycosylation, which is not easily reversible. The more glucose in the blood, the more haemoglobin A 1 C or HbA 1 C will be present in the blood Red cells live for 8-12 weeks (up to 120 days) before they are filtered out of the blood by the spleen and replaced by new RBCs (reticulocytes) from the bone marrow. HbA 1 C levels correlate to the mean plasma glucose level over the previous 8 12 week period, and therefore indicates glucose control over that same period of time Endeavour College of Natural Health endeavour.edu.au 31

32 HBA 1C FORMATION Source: www. medlineplus.com Endeavour College of Natural Health endeavour.edu.au 32

33 HBA 1C Below are two examples of people who have their HbA1c measured. One is poorly controlled, one well controlled. Source: Endeavour College of Natural Health endeavour.edu.au 33

34 Interpreting the Results HIGH Newly diagnosed DM Poorly controlled DM Non-diabetic hyperglycaemia Post-splenectomy Pregnancy LOW Haemolytic anaemia Chronic blood loss Chronic renal failure Endeavour College of Natural Health endeavour.edu.au 34

35 HBA 1C The doctor may order this test if you have diabetes or to screen for diabetes as a measure of your blood sugar control over several months You have more HbA 1 C if you have had high levels of glucose in your blood In general, the higher your HbA 1 C, the higher the risk that you will develop problems such as: Eye disease Heart disease Kidney disease Nerve damage Stroke Endeavour College of Natural Health endeavour.edu.au 35

36 HBA 1c o By a relatively simple calculation, GHb can be correlated accurately with the daily mean plasma glucose (MPG) level, the average glucose level throughout the day (Pagana & Pagana,2014) Endeavour College of Natural Health endeavour.edu.au 36

37 HBA 1C INTERFERING FACTORS Hemoglobinopathies can affect results, because the quantity of haemoglobin A (and, as a result, HbA 1 ) varies considerably inn these diseases Falsely elevated values occur when the RBC lifespan is lengthened because the HbA 1 has a longer period available for glycosylation (e.g. post splenectomy) Ascorbic acid may cause falsely low levels of glycated fructosamine During pregnancy the presence of gestational diabetes will cause a persistently elevated blood glucose resulting in an elevated HbA1C. This should resolve itself up to 3 months post-partum. Endeavour College of Natural Health endeavour.edu.au 37

38 References Mosby s manual of Diagnostic and Laboratory tests, Pagana, Pagana.; 5 th Edition Elsevier Pagana & Pagana, Mosby s Diagnostic and Laboratory Test Reference. 11th edn, Mosby Pocket guide to Diagnostic Tests, D. Nicoll; S.J. McPhee; M. Pignone; C.M. Lu. 5 th ed. McGraw Hill Lange, Web resources date accessed 26/11/2013 National Heart Foundation of Australia and Cardiac Society of Australia and New Zealand. Position statement on lipid management Heart, Lung & Circulation. 2005; 14: Available from url: document/ NHF/lipids_HLCPosStatementFINAL_2005.pdf ol-testing - date accessed 26/11/2010 Endeavour College of Natural Health endeavour.edu.au 38

39 CLASS ROOM ENHANCED ACTIVITY In order to complete this activity please refer to the following: Tutorial activity Instructions (Week Four) Readings (Week Four) SSG (Week Four) Endeavour College of Natural Health endeavour.edu.au 39