Chapter 22 & 33 - Carbohydrates and Diabetes

Match the substance with the effect it has on blood glucose concentration. a. Increases b. Decreases c. Has no effect 1. Exercise 2. C-peptide 3. Somatostatin

1. a 2. c 3. b

Type 2 diabetes mellitus: a. is associated with resistance to the action of insulin. b. is often initially observed in an individual with ketoacidosis. c. is also referred to as gestational diabetes. d. occurs less frequently than type 1 diabetes.

ANS: A At least two major identifiable pathological defects have been reported in individuals with type 2 diabetes. One is a decreased ability of insulin to act on peripheral tissue. This is called insulin resistance and is thought by many to be the primary underlying pathological process. Type 2 is the most prevalent type of diabetes.

A fingerstick glucose value was 120 mg/dL. If unhemolyzed serum or plasma were tested from the same individual at the same time, what might the glucose value be? a. Approximately 132 mg/dL b. Approximately 100 mg/dL c. Approximately 60 mg/dL d. There would be no difference.

ANS: A Because whole blood glucose concentrations are approximately 10% to 15% lower than plasma or serum concentrations, a fingerstick value of 120 mg/dL + 10% of 120 would equal approximately 132 mg/dL.

What effect does epinephrine have on blood glucose value? a. Increases b. Decreases

ANS: A Epinephrine stimulates glycogen breakdown and decreases glucose use, thereby increasing glucose.

What effect does glucagon have on blood glucose value? a. Increases b. Decreases

ANS: A Glucagon stimulates the production of glucose in the liver by glycogenolysis and gluconeogenesis and enhances ketogenesis in the liver.

An example of a monosaccharide would be: a. glucose. b. maltose. c. sucrose. d. starch.

ANS: A Glucose is one of the most common examples of a monosaccharide

Which one of the following 2-hour plasma glucose oral glucose tolerance test (OGTT) results would be classified as diagnostic for impaired glucose tolerance if an individual's fasting blood glucose value is 120 mg/dL (healthy glucose reference interval is 74 to 99 mg/dL)? a. 195 mg/dL b. 105 mg/dL c. 130 mg/dL d. 75 mg/dL

ANS: A Impaired glucose tolerance is diagnosed in people who have fasting blood glucose concentrations less than those required for a diagnosis of diabetes, but have a plasma glucose response during the OGTT between normal and diabetic states. The 2-hour postload plasma glucose following an OGTT is 140 to 199 mg/dL for this classification. An OGTT is required to assign a patient to this class.

Which one of the following has as one of its biological functions the regulation of the lifespan of proteins? a. Glycoproteins b. Glucose c. Lactate d. Ketones

ANS: A Integral membrane proteins have oligosaccharides covalently attached to the extracellular region, forming glycoproteins. One of the biological functions of the carbohydrate chains is to regulate the lifespan of proteins. For example, loss of sialic acid residues from the end of oligosaccharide chains on erythrocytes results in the removal of red blood cells from the circulation.

The breakdown of glycogen stores in the liver to increase serum glucose is referred to as: a. glycogenolysis. b. glycolysis. c. gluconeogenesis. d. glycogenesis.

ANS: A The breakdown of glycogen to glucose and other intermediate products is termed glycogenolysis.

What effect does salicylate have on blood glucose value? a. Increases b. Decreases

ANS: B Certain drugs, including salicylates, produce hypoglycemia.

What effect does ethanol have on blood glucose value? a. Increases b. Decreases

ANS: B Ethanol produces hypoglycemia by inhibiting gluconeogenesis.

Which one of the following coupled-enzyme glucose methods requires extended incubation time to allow for the spontaneous conversion of the alpha-form of glucose to the beta-form so that both forms can react with the initial enzyme in the reaction? a. Hexokinase method b. Glucose oxidase method c. Self-monitoring method d. Polarographic method

ANS: B Glucose oxidase is highly specific for beta-D-glucose. Because 36% and 64% of glucose in solution are in the alpha- and beta-forms, respectively, complete reaction requires mutarotation of the alpha- to beta-form. Extended incubation time allows spontaneous conversion of the alpha-form to the beta-form.

Blood is collected in a tube containing no anticoagulant and is transported uncentrifuged to the laboratory from an outpatient clinic. Transport time at room temperature, accessioning, and sample preparation time equal approximately hours. If a serum glucose level is requested for this tube of blood, how might the results be affected by the timing? a. The glucose value would be decreased by 50%. b. The glucose value would be increased by approximately 15%. c. The glucose value would be decreased by approximately 5%. d. There would be no effect on the glucose value.

ANS: B Glycolysis decreases serum glucose by approximately 5% to 7% in 1 hour (5 to 10 mg/dL) in normal uncentrifuged coagulated blood at room temperature.

Glycated hemoglobins are formed by the addition of glucose to the -terminal residue. a. C; valine b. N; valine c. C; alanine d. N; alanine

ANS: B Hb A1c is formed by the condensation of glucose with the N-terminal valine residue of either beta-chain of Hb A to form an unstable Schiff base.

A type 1 diabetic who is in the early stages of the disease is taken to the emergency room with symptoms of hypoglycemia. Which one of the following endogenous hormones might be the cause of this? a. Epinephrine b. Glucagon c. Cortisol d. Lactate

ANS: B Hypoglycemia occurs frequently in individuals with type 1 or type 2 diabetes. Counterregulatory responses become impaired in type 1 diabetes patients, increasing the risk of hypoglycemia. The secretion of glucagon in response to hypoglycemia is impaired by an unknown mechanism early in the course of type 1 diabetes.

In an individual with a normal hematocrit, whole-blood glucose values are approximately what percent different from plasma glucose values? a. 20% higher b. 10% lower c. 50% higher d. There is no difference between whole blood glucose and plasma glucose values.

ANS: B In individuals with a normal hematocrit, fasting whole-blood glucose concentration is approximately 10% to 12% lower than plasma glucose. While glucose concentrations in the water phase of red blood cells and plasma are similar (the erythrocyte plasma membrane is freely permeable to glucose), the water content of plasma (93%) has a glucose concentration that is approximately 11% higher than that of whole blood.

What is the classic test to determine a diagnosis of hypoglycemia? a. Assessment of fasting blood glucose during a hypoglycemic episode b. A 72-hour fast c. Postprandial glucose analysis d. Oral glucose tolerance test

ANS: B In the classic test a 72-hour fast involves samples being drawn for analysis of plasma glucose, insulin, C-peptide, and proinsulin every 6 hours. When plasma glucose concentration is 60 mg/dL or less, analysis should be performed every 1 to 2 hours. The fast should be concluded when plasma glucose concentration falls to a predetermined concentration (such as 45 mg/dL or less) or the patient exhibits signs or symptoms of hypoglycemia, or after 72 hours. Most patients with true hypoglycemia show an abnormally low value within 12 hours of beginning a fast.

The development of ketoacidosis in an uncontrolled diabetic is caused by the: a. elevated presence of lactic acid. b. increased formation of Beta-hydroxybutyric acid. c. loss of regulation of certain diabetogenes. d. decreased number of insulin receptors on certain cells

ANS: B In uncontrolled diabetes, increased hepatic ketone production and decreased peripheral tissue ketone metabolism leads to acetoacetate accumulation in the blood. A small fraction undergoes spontaneous decarboxylation to form acetone, but the majority is converted to beta hydroxybutyrate. These elevated ketone bodies are the major contributors to the metabolic acidosis that occurs in individuals with diabetic ketoacidosis.

Which one of the following antibodies is found most commonly in over 90% of children who develop type 1 diabetes before 5 years old? a. Islet cell cytoplasmic antibodies b. Insulin autoantibodies c. Insulinoma-associated antigens d. Zinc transporter ZnT8

ANS: B Insulin autoantibodies are present in more than 90% of children who develop type 1 diabetes before 5 years old, but in less than 40% of individuals who develop diabetes after age 12 years.

Factors identified as associated with (and possibly causing) type 1 diabetes mellitus include all of the following except: a. autoimmune reaction. b. insulin resistance. c. genetic factors. d. absolute deficiency of insulin.

ANS: B Insulin resistance is a decreased ability of insulin to act on the receptors in the peripheral tissue and is thought to be the primary underlying pathological process in type 2 diabetes, not type 1 diabetes.

A pregnant woman at 27 weeks gestation is screened for gestational diabetes mellitus. Plasma venous glucose was measured at 1 hour following a 50 g oral glucose load. What value must this glucose be above or equal to for a glucose tolerance test to be performed? a. The value must be remain within healthy glucose reference interval. b. The value must be 140 mg/dL glucose. c. The value must be 200 mg/dL glucose. d. The value must be 500 mg/dL glucose.

ANS: B See Table 33-2. A plasma glucose value greater than or equal to 140 mg/dL (7.7 mmol/L) at 1 hour after glucose ingestion indicates the necessity for definitive testing. Approximately 15% of pregnant women meet this criterion and require a full OGTT.

What effect does septicemia have on blood glucose value? a. Increases b. Decreases

ANS: B Septicemia depletes glycogen stores, impairs gluconeogenesis, and increases peripheral use of glucose.

The hyperglycemia observed in a diabetic causes many toxic effects such as retinopathy and nephropathy. Although it is unclear how these outcomes are caused by elevated blood sugar, it is thought that hyperglycemia: a. causes increased serum osmolarity, which leads to decreased blood flow in the microvascular compartments in peripheral tissues. b. causes increased production of advanced glycation end products, which might contribute to microvascular complications. c. induces secretion of glucagon, which antagonizes insulin secretion and leads to destruction of the microvessels in the retina and kidney. d. causes a hemolytic disease with shortened red blood cell survival, thus not providing enough oxygen to peripheral tissues.

ANS: B The molecular mechanism by which hyperglycemia produces toxic effects is unknown, but glycation of tissue proteins may be important. Hyperglycemia accelerates the formation of protein-bound AGE, and patients with diabetes thus have more AGE than healthy subjects. Through effects on the functional properties of protein and extracellular matrix, AGE may contribute to the microvascular and macrovascular complications of diabetes.

Retinopathy, neuropathy, microvascular, and macrovascular changes are all chronic complications of both type 1 and type 2 diabetes mellitus. One theory as to the cause of these chronic problems is the elevation of advance glycation end (AGE) products. These AGE products consist of: a. glucose transporter proteins that promote the uptake of glucose from the lumen of the small bowel. b. hemoglobin that has a glucose attached to the N-terminal valine residue of either beta-chain of hemoglobin A. c. proteins that have been irreversibly modified by nonenzymatic attachment of glucose. d. glycated genes that contribute to the development of diabetes and the formation of diabetogenes.

ANS: C AGE products are proteins that have been irreversibly modified by nonenzymatic attachment of glucose and may contribute to the chronic complications of diabetes.

A woman visits her physician with a complaint of polyuria and polydipsia. She has a family history of type 2 diabetes mellitus and is concerned that she is developing the disease. The physician notes that her previous hemoglobin A1c (Hb A1c) value was 6% (considered within healthy reference interval in the physician's practice) with a fasting plasma glucose of 95 mg/dL. At this visit, her Hb A1c value is 8.5%. Why would the physician be correct to order an oral glucose tolerance test (OGTT) for this individual? a. The Hb A1c result indicates that glycation of proteins has increased producing elevated advanced glycation end products and the possible onset of type 2 diabetes. An OGTT would help to confirm this. b. The Hb A1c result indicates that diabetic nephropathy is occurring, signaling the possible onset of type 2 diabetes. An OGTT would help to confirm this. c. The Hb A1c result indicates an increase in average blood glucose and possible onset of type 2 diabetes. An OGTT would help to confirm this. d. The physician would not be correct in ordering an OGTT because there is no indication that there is an onset of type 2 diabetes from the given laboratory values.

ANS: C Because each 1% change in Hb A1c represents an approximate 30 mg/dL change in average blood glucose, the woman's average glucose might be or have been elevated to over 170 mg/dL. Fasting blood glucose concentration of 126 mg/dL is one of the diagnostic criteria for diabetes mellitus as are specific results of an OGTT.

High albuminuria is defined as: a. a large albumin molecule that is present only in urine and that is measured by the lab in preclinical screening for diabetes. b. an albumin molecule that is larger and less functional because of the effects of hyperglycemia that is measured by the laboratory in the clinical diagnosis of diabetes. c. increased urinary albumin excretion between the range of 20 to 200 µg/min that is measured by the laboratory in the chronic management of diabetes mellitus. d. a long-lived glycated albumin molecule found in the urine of a type 2 diabetic and measured by the laboratory in the acute management of a diabetic.

ANS: C Before the detection of persistent proteinuria (a urinary albumin excretion, UAE, rate 200 µg/min) observed in overt diabetic nephropathy, a stage of increased UAE occurs that is not detected by routine methods. This range of 20 to 200 µg/min is termed high albuminuria. The clinical laboratory has a vital role in both the diagnosis and management of diabetes. Laboratory detection of and monitoring complications as part of the chronic management of diabetes is achieved by assaying creatinine, urine albumin, and serum lipids. See Table 33-3.

By what mechanism does glucagon promote hyperglycemia? a. Glucagon promotes glycogenesis. b. Glucagon stimulates insulin release. c. Glucagon stimulates glucose synthesis by gluconeogenesis. d. Glucagon promotes hypoglycemia, not hyperglycemia.

ANS: C Glucagon stimulates the production of glucose in the liver by glycogenolysis and gluconeogenesis.

A heparinized blood sample is received in the chemistry laboratory. After centrifugation, the plasma appears markedly hemolyzed. If the hexokinase method is used in this lab to measure glucose, why should this specimen be re-collected? a. Heparin interferes with the second enzyme in the hexokinase assay. b. Hemoglobin competes with the chromogen for hydrogen peroxide and inhibits the hexokinase reaction. c. Red blood cells contain phosphate esters and enzymes that interfere with the hexokinase assay. d. There is no need for re-collection as neither hemolysis nor heparin interfere with the hexokinase assay.

ANS: C Hemolyzed specimens containing more than 0.5 g of hemoglobin/dL are unsatisfactory because phosphate esters and enzymes released from red blood cells interfere with the assay.

Which of the following is characteristic of type 1A diabetes mellitus? a. Normal blood insulin levels b. Lack or decrease of functional insulin receptors on cells c. Circulating autoantibodies formed against pancreatic insulin-secreting cells. d. Individuals with this type of diabetes are not prone to ketosis.

ANS: C Immune-mediated diabetes or type 1A is caused by cellular-mediated autoimmune destruction of the insulin-secreting cells of pancreatic beta-cells, typically mediated by T cells.

In uncontrolled diabetes mellitus, excess ketones are present in the blood and urine because of: a. decreased lipid formation. b. increased glycolysis. c. increased breakdown of lipids (lipolysis). d. increased glucose uptake into cells.

ANS: C In uncontrolled diabetes, the low insulin concentration result in increased lipolysis and decreased reesterification, thereby increasing plasma free fatty acids. In addition, the increased glucagon/insulin ratio enhances fatty acid oxidation in the liver. Increased counter-regulatory hormones also augment lipolysis and ketogenesis in fat and liver, respectively. Thus increased hepatic ketone production and decreased peripheral tissue metabolism lead to acetoacetate accumulation in the blood.

An individual with a severe, uncontrolled case of type 1 diabetes mellitus will exhibit all of the following laboratory results except: a. hyperlipidemia. b. hyperglycemia. c. hyperinsulinemia. d. decreased blood pH with increased ketone bodies.

ANS: C Individuals with uncontrolled type 1 diabetes typically have hypoinsulinemia, which leads to elevated lipids, glucose, and ketones.

A 75-year-old man was brought by his daughter to a hospital emergency department. He was in a confused state, trembling, sweating, with a rapid pulse, lightheadedness, and complaining of hunger and epigastric discomfort. His daughter claims that he does not drink alcohol and that he takes oral hypoglycemic drugs to control his diabetes. What is the likely cause of his symptoms? a. The oral hypoglycemic drugs are affecting his thyroid gland. b. He is likely suffering from pheochromocytoma and the effects of increased epinephrine. c. He has possibly taken too much of his medication and is suffering from hypoglycemia. d. His diabetes is not being adequately controlled and is leading to lactic alkalosis

ANS: C Oral hypoglycemic agents are the most frequent cause of drug-induced hypoglycemia. The symptoms indicate hypoglycemia, which is not consistent with the symptoms in Options a and b. Lactic acidosis might cause these symptoms, but not alkalosis.

The major storage carbohydrate in animals is , which is located most abundantly in a. cellulose; vegetable fibers b. glycoprotein; cell membranes c. glycogen; the liver d. starch; skeletal muscle

ANS: C The major storage carbohydrates are starch in plants and glycogen in animals, and glycogen is most abundant in the liver and also is found in skeletal muscle.

Determining urinary albumin excretion (UAE) is critical in type 1 and type 2 diabetics because: a. this indicates increased attachment of glucose to proteins, lipids, and nucleic acids that contribute to the microvascular complications of diabetes. b. UAE increase indicates increased glycation of serum albumin that forms fructosamine and leads to ketoacidosis. c. increased UAE is highly predictive of and is thought to precede diabetic nephropathy and end-stage renal disease. d. it assesses the long-term blood glucose concentration in a diabetic to monitor glucose control over an 8- to 12-week period.

ANS: C The presence of increased UAE denotes an increase in the transcapillary escape rate of albumin and therefore is a marker of microvascular disease. Increased UAE precedes and is highly predictive of diabetic nephropathy, end-stage renal disease, cardiovascular mortality, and total mortality in patients with diabetes.

Although not a routine clinical laboratory screening test, measurement of insulin secretion in a potential diabetic is important because: a. an increase in insulin indicates the onset of hypoglycemia and the presence of advanced glycation end products. b. increased insulin leads to retinopathy, nephropathy, and neuropathy. c. a decrease in insulin will cause overstimulation of the GLUT4 transporter and low blood glucose. d. a decrease in glucose-stimulated insulin secretion is the first functional abnormality in both types of diabetes.

ANS: D A decrease in glucose-stimulated insulin secretion is the first functional abnormality in both type 1 and type 2 diabetes; however, tests of insulin secretion are not currently recommended for routine clinical use.

Insulin regulates blood glucose levels by: a. enhancing glycogenolysis, gluconeogenesis, and ketogenesis in the liver. b. stimulating gluconeogenesis and increasing the breakdown of protein and fat. c. inhibiting release of growth hormone from the pituitary and inhibiting secretion of glucagon by the pancreas. d. stimulating the translocation of a glucose transporter and promoting glucose uptake into skeletal muscle and fat.

ANS: D After a meal, the pancreas releases insulin, which stimulates the translocation of GLUT4 to the plasma membrane, thereby promoting glucose uptake into skeletal muscle and fat.

Hb A1c makes up approximately what percentage of total Hb A1? a. 10% b. 25% c. 50% d. 80%

ANS: D Chromatographic analysis of Hb A identifies several minor hemoglobins, namely, Hb A1a, Hb A1b, and Hb A1c, which are collectively referred to as Hb A1. Hb A1c is the major fraction, constituting approximately 80% of Hb A1.

As a counter-regulator of glucose metabolism in a healthy individual, epinephrine has the effect of blood glucose. a. breaking down glucose to form glycogen to increase b. inducing liver gluconeogenesis to decrease c. increasing glucose uptake by cells to decrease d. stimulating glycogenolysis to increase

ANS: D Epinephrine, a catecholamine secreted by the adrenal medulla, stimulates glucose production (glycogenolysis) and decreases glucose use, thereby increasing blood glucose concentration. It also stimulates glucagon secretion and inhibits insulin secretion by the pancreas.

Glucagon is made by the alpha-cells in the pancreas and when released causes elevated blood glucose. By what mechanism does glucagon promote hyperglycemia? a. Glucagon promotes hypoglycemia, not hyperglycemia. b. Glucagon stimulates insulin release c. Glucagon promotes glycogenesis in all cells. d. Glucagon stimulates glycogenolysis and gluconeogenesis

ANS: D Glucagon stimulates the production of glucose in the liver by glycogenolysis and gluconeogenesis.

The glucose assay on an analyzer uses hexokinase as the enzyme that phosphorylates glucose. What are the initial products formed from the first step of this reaction? a. Nicotinamide adenine dinucleotide and NADH b. 6-Phosphogluconate and hydrogen ions c. Glycosylated hemoglobin d. Glucose-6-phosphate and adenosine diphosphate (ADP)

ANS: D In the hexokinase (HK) method of glucose determination, glucose is first phosphorylated by adenosine triphosphate (ATP) in the presence of HK and Mg2+. Glucose-6-phosphate and ADP are the products of this initial step.

Insulin deficiency in diabetes mellitus will cause: a. increased insulin resistance and hyperglycemia. b. increased glucose uptake by cells leading to hyperglycemia and cell death. c. decreased lipolysis leading to ketosis. d. increased glucagon concentration, which contributes to hyperglycemia and ketosis.

ANS: D Increased glucagon concentrations, secondary to insulin deficiency, are believed to contribute to the hyperglycemia and ketosis of diabetes. Low insulin concentrations result in increased lipolysis and decreased re-esterification of fatty acids into triglycerides, and increased plasma-free fatty acids.

The role of the clinical laboratory in diagnosis of diabetes mellitus involves initial diagnostic criteria. For many years, the only diagnostic criterion required was demonstration of hyperglycemia in two or more fasting plasma glucose tests. What other laboratory analysis is now considered to be useful as a diagnostic criterion? a. Demonstration of impaired glucose tolerance in the OGTT b. Consistent hyperglycemia after a 72-hour fast c. Presence of ketones in urine on more than one occasion d. Demonstration of elevated hemoglobin A1c

ANS: D Several influential clinical organizations now include hemoglobin A1c (Hb A1c), which reflects long-term blood glucose concentrations, as a diagnostic criterion for diabetes. This analysis is particularly useful in the diagnosis of type 2 diabetes when hyperglycemia often is not severe enough for an individual to notice symptoms of diabetes.

Conversion of glucose into lactate or pyruvate is referred to as: a. glycogenesis. b. glycogenolysis. c. glyconeogenesis. d. glycolysis.

ANS: D The conversion or oxidation of glucose or other hexoses into lactate or pyruvate is called glycolysis. Glycolysis is the initial process of carbohydrate metabolism.

The syndrome that is considered a collection of associated clinical and laboratory findings that include insulin resistance, hyperinsulinemia, obesity, high triglyceride and low high-density lipoprotein (HDL) cholesterol, and hypertension is the: a. glucotoxic syndrome. b. type 1A diabetes mellitus syndrome. c. glucose counter-regulatory syndrome. d. insulin resistance syndrome.

ANS: D The insulin resistance syndrome (also known as syndrome X, or the metabolic syndrome) is a constellation of associated clinical and laboratory findings, consisting of insulin resistance, hyperinsulinemia, obesity, dyslipidemia (high triglyceride and low high-density lipoprotein [HDL] cholesterol), and hypertension. Individuals with this syndrome are at increased risk for cardiovascular disease.