Clinical Chemistry (Carbohydrates) Flashcards
145 - 178 (34 cards)
What does hydrolysis of sucrose yield?
A. Glucose only
B. Galactose and glucose
C. Maltose and glucose
D. Fructose and glucose
D
When two monosaccharides condense with loss of a molecule of water, a disaccharide is formed. Disaccharides, therefore, can be hydrolyzed into two monosaccharides. The most important disaccharides are maltose, lactose, and sucrose. On hydrolysis, sucrose will yield one molecule of glucose and one molecule of fructose. Maltose can be hydrolyzed into two molecules of
glucose. Lactose can be hydrolyzed into glucose and galactose
In what form is glucose stored in muscle and liver?
A. Glycogen
B. Maltose
C. Lactose
D. Starch
A
Glycogen is a polysaccharide composed of many glucose molecules. In contrast to the amylopectin molecule, a glycogen molecule is more highly branched and more compact. Glycogen is found in a variety of animal tissues, particularly in the liver, and provides the storage form for carbohydrates in the body. When energy requirements warrant it, glycogen may be broken down to glucose by a series of phosphorylating and related enzymes.
Which of the following carbohydrates is a polysaccharide?
A. Starch
B. Sucrose
C. Lactose
D. Glucose
A
There are three major classifications of carbohydrates: monosaccharides, disaccharides, and polysaccharides. Starch is classified as a polysaccharide because its structure is composed of many molecules of glucose (a monosaccharide) condensed together
Which of the following defines the term “glycolysis”?
A. Conversion of glucose into lactate or pyruvate
B. Conversion of glucose to glycogen
C. Breakdown of glycogen to form glucose
D. Breakdown of lipids to form glucose
A
The level of glucose in the blood is a result of a variety of metabolic processes. Processes that increase the blood glucose include ingestion
of sugar, synthesis of glucose from noncarbohydrate sources, and breakdown of glycogen. Processes that decrease blood glucose include metabolizing glucose to produce energy and converting glucose to glycogen or fat. Glycogen is a polysaccharide, which is the storage form of carbohydrates in animals. Glycogenesis refers to
the formation of glycogen in the liver from blood glucose. This occurs in response to increased blood glucose levels. In response to decreasing blood glucose levels, glycogen in the liver is broken down to glucose. This process is called glycogenolysis. When glucose is metabolized, for example, to produce energy, it is converted to lactate or pyruvate. This process is called glycolysis. When the body synthesizes glucose from noncarbohydrate sources—that is, amino acids, glycerol, or lactate—the process is called gluconeogenesis. When the body uses glucose to synthesize fat, this process is called
lipogenesis.
What is the glucose concentration in fasting whole blood?
A. Less than the concentration in plasma or serum
B. Greater than the concentration in plasma or serum
C. Equal to the concentration in plasma or serum
D. Meaningless because it is not stable
A
When highly specific analytical methods are used, the glucose concentration in fasting whole blood is approximately 12-15% lower than in plasma or serum. Although glucose diffuses freely between the water phase of plasma and red blood cells, there is a higher concentration of water in plasma (approximately 12%) than in
whole blood, accounting for the increased glucose concentration in plasma. The water content of whole blood depends on the hematocrit.
Of the following blood glucose levels, which would you expect to result in glucose in the urine?
A. 60mg/dL
B. 120mg/dL
C. 150mg/dL
D. 225mg/dL
D
Renal threshold is defined as the plasma level that must be exceeded in order for the substance to appear in the urine. The renal threshold for glucose is 180 mg/dL. This means that the blood glucose level must exceed 180 mg/dL in order for glucose to be excreted in the urine
Which test may be performed to assess the average plasma glucose level that an individual maintained during a previous 2- to 3-month period?
A. Plasma glucose
B. Two-hour postprandial glucose
C. Oral glucose tolerance
D. Glycated hemoglobin
D
Glycated hemoglobin is a collective term encompassing the three glycated hemoglobin fractions—hemoglobin A)a , hemoglobin Alb,
and hemoglobin Alc. Hb Alc is the fraction of Hb AI that is present in the greatest concentration. Some commercially available column chromatography methods measure the three fractions collectively. Glycated hemoglobin refers to the specific red cell hemoglobin A types to which a glucose molecule becomes irreversibly attached. The greater the glucose concentration in the plasma, the greater the number of hemoglobin molecules that will become glycated. Because red blood cells have an average life span of 120 days and the glycation is irreversible, measurement of glycated hemoglobin reflects the average plasma glucose level of an individual during the previous 2- to 3-month period. This test is used as a monitor of diabetic control.
The physician determined that the patient needed an oral glucose tolerance test (OGTT) to assist in diagnosis. The patient had blood drawn for the OGTT, and the following serum glucose results were obtained. These results are indicative of what state?
Fasting serum glucose 124 mg/dL
2-hour post-load serum glucose 227 mg/dL
A. Normal
B. Diabetes mellitus
C. Addison disease
D. Hyperinsulinism
B
The patient presents as having diabetes mellitus. The American Diabetes Association (ADA) published updated standards in 2007 for the classification and diagnosis of diabetes mellitus. Three criteria have been defined, with only one needing to be present to establish the diagnosis of diabetes rnellitus. The three criteria include classic diabetic symptoms and a casual plasma glucose of >200 mg/dL, a fasting plasma glucose of S:126 mg/dL, and a 2-hour postload plasma
glucose (part of OGTT) of >200 mg/dL. It is recommended that any positive test be repeated on a subsequent day, if possible, to confirm the diagnosis. It should be noted that the OGTT is not recommended for routine clinical use and would be used only in special circumstances
A 30-year-old pregnant woman has a gestational diabetes mellitus screening test performed at 26 weeks of gestation. Her physician chooses to order a 50-g oral glucose load. Her serum glucose level is 150 mg/dL at 1 hour. What should occur next?
A. This confirms diabetes mellitus; give insulin.
B. This confirms diabetes mellitus; dietary intake of carbohydrates should be lessened.
C. This is suspicious of diabetes mellitus; an oral glucose tolerance test should be performed.
D. This is an expected glucose level in a pregnant woman.
C
Increased insulin resistance is commonly seen in the late second and third trimesters of pregnancy. Most women are able to compensate
by secreting additional insulin and, thus, are able to maintain normal blood glucose levels. In cases of gestational diabetes mellitus, women
are unable to make sufficient insulin to meet their needs. In the screening test, serum glucose is assessed at 1 hour following the ingestion of a 50-gram glucose load (glucose challenge test). If
the serum glucose is >140 mg/dL, the next step is to perform an oral glucose tolerance test
A sample of blood is collected for glucose in a sodium fluoride tube before the patient has had breakfast. The physician calls 2 hours later and requests that determination of blood urea nitrogen (BUN) be performed on the same sample rather than obtaining another specimen. The automated analyzer in your laboratory utilizes the urease method to quantify BUN. What should you tell the physician?
A. Will gladly do the test if sufficient specimen remains
B. Could do the test using a micromethod
C. Can do the BUN determination on the automated analyzer
D. Cannot perform the procedure
D
Sodium fluoride is a weak anticoagulant that acts as a preservative for glucose. It functions as a glucose preservative by inhibiting glycolysis.
However, it is not suitable for use with many enzyme procedures. In the determination of BUN, where urease activity is utilized, the high concentration of fluoride in the plasma acts as an enzyme inhibitor, preventing the necessary chemical reaction
Which of the following does not properly describe type 1 diabetes mellitus?
A. Insulin deficiency
B. Associated with autoimmune destruction of pancreatic B-cells
C. Ketoacidosis prone
D. Occurs more frequently in adults
D
Based on the biochemistry of the disease, diabetes mellitus has been classified as type 1 and type 2. Type 1 occurs more commonly in
individuals under 20 years of age. Studies suggest that type 1 is associated with autoimmune destruction of (3-cells, and it is characterized by nsulin deficiency and thus a dependency on
injection of insulin. Unlike people afflicted with type 2, type 1 individuals are prone to ketoacidosis and to such complications as angiopathy, cataracts, nephropathy, and neuropathy.
Which of the following is not associated with insulin?
A. Synthesized from proinsulin
B. Synthesized by B-cells in the pancreas
C. C-peptide is active form
D. Two-chain polypeptide
C
The protein hormone insulin is synthesized in the pancreas by the (3-cells of the islets of Langerhans. Insulin, a two-chain polypeptide,
consists of 51 amino acids. A single-chain preproinsulin is cleaved to proinsulin, which is the immediate precursor of insulin. Proinsulin is hydrolyzed to form insulin, a two-chain polypeptide, and inactive C-peptide. Insulin promotes the entry of glucose into tissue cells.
Which of the following statements may be associated with the activity of insulin?
A. Increases blood glucose levels
B. Decreases glucose uptake by muscle and fat cells
C. Stimulates release of hepatic glucose into the blood
D. Stimulates glycogenesis in the liver
D
Insulin may be described as an anabolic, polypeptide hormone. Insulin stimulates glucose uptake by muscle cells (which increases protein synthesis), by fat cells (which increases triglyceride synthesis), and by liver cells (which increases lipid synthesis and glycogenesis). If cellular uptake of glucose is stimulated, the glucose concentration in the circulation decreases
Which of the following is not characteristic of severe hyperglycemia?
A. Polyuria
B. Ketonuria
C. Glycosuria
D. Hypoglucagonemia
D
In uncontrolled diabetes mellitus, the blood glucose level exceeds the renal threshold of approximately 180 mg/dL for glucose, leading to glycosuria and polyuria. The excess secretion of glucagon stimulates lipolysis, with increased formation of acetoacetic acid. In the blood, the ketoacids dissociate, with the hydrogen ions being buffered by bicarbonate. This causes the bicarbonate to become depleted and leads to metabolic acidosis.
Which of the following statements applies to the preferred use of plasma or serum, rather than whole blood, for glucose determination?
A. Glucose is more stable in separated plasma or serum.
B. Specificity for glucose is higher with most methods when plasma or serum is used.
C. It is convenient to use serum or plasma with automated instruments because whole blood requires mixing immediately before sampling.
D. All the above.
D
Glucose determinations are generally performed on serum or plasma rather than whole blood. Serum or plasma is more convenient to
use than whole blood in most automated systems because serum does not require mixing before sampling. Glucose stability is greater in separated plasma than in whole blood because glycolysis is minimized. Specificity for glucose is higher when plasma or serum is used because variations attributable to interfering substances in the red cells are avoided.
Which of the following analytes would not commonly be measured when monitoring complications of diabetes mellitus?
A. Serum urea nitrogen
B. Urinary albumin
C. Serum creatinine
D. Serum bilirubin
D
Research has demonstrated that there is a correlation between blood glucose levels in diabetes mellitus and the development of long term complications. These complications may include such disorders as retinopathy, neuropathy, atherosclerosis, and renal failure. Thus, quantifying such blood analytes as urea, creatinine, and lipids as well as urinary albumin can aid in monitoring diabetic individuals.
Ingestion of which of the following drugs may cause hypoglycemia?
A. Ethanol
B. Propranolol
C. Salicylate
D. All the above
D
There are greater than 100 causes of hypoglycemia. Among the causes is the ingestion of certain drugs. Use of ethanol, propranolol, and salicylate has been linked to the occurrence of hypoglycemia.
Which of the following is not associated with hypoglycemia?
A. Neuroglycopenia
B. Symptoms occur with plasma glucose level of 60-70 mg/dL
C. Decreased hepatic glucose production
D. Diagnostic test is 72-hour fast
B
The diagnostic test for hypoglycemia is the 72-hour fast, which requires the analysis of glucose, insulin, C-peptide, and proinsulin at 6- hour intervals. The test should be concluded when plasma glucose levels drop to < 45 mg/dL, when hypoglycemic symptoms appear, or after 72 hours have elapsed. In general, hypoglycemic symptoms occur when the plasma glucose level falls below 55 mg/dL. Such symptoms may include headache, confusion, blurred vision, dizziness, and seizures. The term “neuroglycopenia” has been applied to these central nervous system disorders. Although decreased hepatic glucose production and increased glucose utilization may cause hypoglycemia, there are over 100 causes of this disorder
Which glucose method can employ a polarographic oxygen electrode?
A. Hexokinase
B. Glucose oxidase
C. Glucose dehydrogenase
D. o-Toluidine
B
Glucose in the presence of oxygen is oxidized to gluconic acid and hydrogen peroxide. This reaction is catalyzed by glucose oxidase. By using a polarographic oxygen electrode, the rate of oxygen consumption is measured and related to the concentration of glucose in the sample
Which glucose method catalyzes the phosphorylation of glucose by adenosine triphosphate, forming glucose-6-phosphate and adenosine diphosphate with the absorbance of the NADPH product read at 340 nm?
A. o-Toluidine
B. Glucose oxidase
C. Hexokinase
D. Glucose dehydrogenase
C
The hexokinase method for quantifying glucose uses two coupled enzymatic reactions. In the first reaction, which is catalyzed by hexokinase, glucose is phosphorylated by adenosine triphosphate, forming glucose-6-phosphate and adenosine diphosphate. In the second reaction, glucose-6-phosphate dehydrogenase (derived from yeast) catalyzes the oxidation of glucose-6- phosphate and the reduction of nicotinamide adenine dinucleotide phosphate. The amount of reduced NADPH formed is proportional to the glucose concentration in the sample. Thus, the greater the absorbance reading of NADPH at 340 nm, the greater is the glucose concentration. If bacterial G-6-PD is used, the cofactor is NAD+ with the production of NADH.
Which of the following is not a reagent required in an enzymatic serum glucose method?
A. NAD+
B. Glucose oxidase
C. Peroxidase
D. Reduced chromogen
A
The glucose oxidase method for quantifying glucose employs two coupled enzymatic reactions. In the first reaction, which is catalyzed by glucose oxidase, glucose in the presence of oxygen is oxidized to gluconic acid and hydrogen peroxide. In the second reaction, peroxidase catalyzes a reaction between hydrogen peroxide and the reduced form of a chromogenic oxygen acceptor, such as o-dianisidine, forming an oxidized colored product that is read spectrophotometrically
Which of the following glucose methods should not be used during the administration of an oral xylose absorption test?
A. Glucose oxidase—colorimetric
B. Glucose oxidase—polarographic
C. Glucose dehydrogenase
D. Hexokinase
C
The glucose dehydrogenase method uses only one enzymatic reaction for the measurement of glucose in a sample. Glucose dehydrogenase catalyzes the oxidation of glucose and the reduction of nicotinamide adenine dinucleotide. The amount of reduced NADH formed is proportional to the glucose concentration in the sample. When measuring blood glucose levels during the administration of an oral xylose tolerance test, the glucose dehydrogenase method should not be used, because the relative rate of reaction of Dxylose as compared to glucose is 15% with this method. In contrast, D-xylose will not react in the hexokinase and glucose oxidase methods, thus allowing glucose to be measured accurately. The D-xylose absorption test is useful in distinguishing two types of malabsorption: intestinal malabsorption and malabsorption resulting from pancreatic insufficiency. When D-xylose is administered orally, it is absorbed by passive diffusion into the portal vein from the proximal portion of the small intestine. Because D-xylose is not metabolized by the liver, it is excreted unchanged by the kidneys. In intestinal malabsorption, the
amount of D-xylose excreted, as measured in a 5-hour urine specimen, is less than normal because of decreased absorption of D-xylose. In malabsorption caused by pancreatic insufficiency, the absorption of D-xylose is normal
Which glucose method is considered to be the reference method?
A. Glucose oxidase
B. o-Toluidine
C. Hexokinase
D. Glucose dehydrogenase
C
Although there are several reliable enzymatic glucose methods available, the hexokinase method is the reference method for quantifying glucose. The reference method requires that a protein-free filtrate be made using barium hydroxide and zinc sulfate. The clear supernatant is then used as the sample in the hexokinase/glucose-6-phosphate dehydrogenase coupled enzyme reactions. For routine clinical use, serum is used directly in the hexokinase method because deproteinization is too time-consuming
An individual has a plasma glucose level of 110 mg/dL. What would be the approximate glucose concentration in this patient’s cerebrospinal fluid?
A. 33 mg/dL
B. 55 mg/dL
C. 66 mg/dL
D. 110 mg/dL
C
The reference interval for glucose in CSF is 60% of the normal plasma value. For a plasma glucose of 110 mg/dL, the expected CSF glucose level would be 66 mg/dL. The equilibration of CSF with plasma glucose takes several hours. The reference interval for the CSF glucose level
is 40-70 mg/dL as compared with a normal fasting plasma glucose level. Low levels of CSF glucose are associated with a number of diseases including bacterial meningitis and tuberculous meningitis, whereas viral disease generally presents with a normal level of CSF glucose
