Welcome to Part 47 of the ASCP MLS Exam Practice Series, focusing on Biochemistry – Carbohydrate Metabolism and Glucose Regulation. This chapter reviews the biochemical pathways that provide energy to the body and explains how carbohydrate metabolism is measured, regulated, and interpreted in the clinical laboratory. A clear understanding of glucose homeostasis and metabolic disorders such as diabetes mellitus is essential for accurate laboratory analysis and effective patient management.
📘 Key Topics Covered
- Structure, classification, and biological roles of carbohydrates
- Glycolysis, glycogenolysis, glycogenesis, gluconeogenesis
- Krebs (TCA) cycle and oxidative phosphorylation overview
- Hormonal regulation – insulin, glucagon, epinephrine, cortisol
- Carbohydrate metabolism disorders: diabetes, hypoglycemia, glycogen storage diseases
- Laboratory methods for glucose determination (hexokinase, GOD-POD, glucose oxidase)
- Glucose tolerance testing (GTT) and HbA1c interpretation
- Quality control and reference ranges in carbohydrate testing
🧠 Learning Objectives
By the end of this part, you should be able to:
- Interpret laboratory tests for diagnosing and monitoring diabetes mellitus.
- Describe the main biochemical pathways of carbohydrate metabolism.
- Explain hormonal control of blood-glucose levels.
- Recognize common metabolic disorders linked to carbohydrate imbalance.
60 MCQs (3761 – 3820):
- Following overnight fasting, hypoglycemia in a non-diabetic adult male is defined as a glucose level at or below:
a) ≤70 mg/dL (≤3.9 mmol/L)
b) ≤60 mg/dL (≤3.3 mmol/L)
c) ≤55 mg/dL (≤3.0 mmol/L)
d) ≤45 mg/dL (≤2.5 mmol/L) - The metabolic process that describes the conversion of glucose or other hexoses into lactate or pyruvate is called:
a) Glycogenesis
b) Glycogenolysis
c) Gluconeogenesis
d) Glycolysis - For a healthy person with a blood glucose of 80 mg/dL (4.4 mmol/L), what would the simultaneously determined cerebrospinal fluid (CSF) glucose value most likely be?
a) 25 mg/dL (1.4 mmol/L)
b) 50 mg/dL (2.3 mmol/L)
c) 100 mg/dL (5.5 mmol/L)
d) 150 mg/dL (8.3 mmol/L) - Which of the following fasting plasma glucose results is diagnostic of diabetes mellitus?
a) 110 mg/dL (6.1 mmol/L)
b) 120 mg/dL (6.7 mmol/L)
c) 126 mg/dL (6.9 mmol/L)
d) 140 mg/dL (7.8 mmol/L) - The best laboratory test to monitor long-term glucose control in a patient with type 2 diabetes mellitus is the measurement of:
a) Weekly fasting serum glucose
b) 2-hour postprandial serum glucose
c) Fructosamine
d) HbA1c - What is the primary reason a cerebrospinal fluid (CSF) specimen for glucose analysis should be analyzed immediately?
a) To prevent contamination
b) To avoid precipitation of proteins
c) To minimize glycolysis by cells or bacteria
d) To ensure accurate electrolyte measurement - The hormone secreted in response to falling blood glucose levels mid-morning is:
a) Insulin
b) Cortisol
c) Epinephrine
d) Glucagon - In a non-fasting state, how does the glucose concentration in arterial/capillary blood typically compare to venous blood?
a) It is approximately 1-5 mg/dL lower
b) It is approximately 1-5 mg/dL higher
c) It is approximately 10-15 mg/dL lower
d) It is identical - Sodium fluoride is added to blood collection tubes for glucose testing primarily to:
a) Serve as a coenzyme for the hexokinase reaction
b) Precipitate proteins for a clearer sample
c) Inhibit glycolysis by white blood cells
d) Prevent reactivity of non-glucose reducing substances - Which of the following 2-hour postprandial glucose values is diagnostic of diabetes mellitus?
a) 150 mg/dL (8.3 mmol/L)
b) 170 mg/dL (9.4 mmol/L)
c) 180 mg/dL (9.9 mmol/L)
d) 200 mg/dL (11.0 mmol/L) - The most specific enzymatic method for the assay of glucose in all body fluids utilizes:
a) Glucose Oxidase
b) Glucose Dehydrogenase
c) Glucose-6-Phosphatase
d) Hexokinase - A patient with hemolytic anemia will typically show which of the following in a glycated hemoglobin (HbA1c) test?
a) A decrease in the glycated Hb value
b) An increase in the glycated Hb value
c) Little or no change in the glycated Hb value
d) An elevated HbA2 value - The total glycosylated hemoglobin level in a hemolysate reflects the:
a) Blood glucose level at the time the sample is drawn
b) Average blood glucose levels for the past week
c) Average blood glucose levels of the past 2-3 months
d) HbA1c level at the time the sample is drawn - An increase in serum acetone is most indicative of a defect in the metabolism of:
a) Carbohydrates
b) Fats
c) Urea Nitrogen
d) Uric Acid - Which of the following tests is considered the best method to diagnose lactase deficiency?
a) Plasma Aldolase level
b) D-xylose test
c) H2 Breath Test
d) Lactate Dehydrogenase (LD) level - Why is a serum glucose value higher than a whole blood glucose value from the same patient at the same time?
a) Serum has a lower water content than whole blood.
b) Glucose is consumed by platelets during clotting.
c) The true glucose concentration is a function of the hematocrit.
d) Serum has fewer interfering substances. - If a patient vomits 90 minutes into a standard oral glucose tolerance test (OGTT), the best course of action is to:
a) Give the patient orange juice and continue the test.
b) Start the test over immediately with a 50 g carbohydrate dose.
c) Draw a blood sample for glucose and then discontinue the test.
d) Place the patient in a recumbent position and continue the test. - The different water content of erythrocytes and plasma makes the true glucose concentration in whole blood a function of the:
a) Leukocyte Count
b) Hemoglobin Concentration
c) Hematocrit
d) Erythrocyte Indices - Which of the following statements best describes the preparation of a patient for a standard glucose tolerance test?
a) A low carbohydrate diet for 3 days
b) Fasting for 48 hours prior to testing
c) A high carbohydrate diet for 3 days
d) Bed rest for 3 days - In the hexokinase method for glucose determination, the actual end product measured is:
a) The amount of hydrogen peroxide produced.
b) The NADH produced from the reduction of NAD.
c) The condensation of glucose with an aromatic amine.
d) The amount of glucose combined with bromcresol purple. - Pregnant women with symptoms of thirst, frequent urination, or unexplained weight loss should have which of the following tests performed?
a) Tolbutamide Test
b) Lactose Tolerance Test
c) Epinephrine Tolerance Test
d) Glucose Tolerance Test - The recommended glycosylated hemoglobin test for monitoring diabetic patients according to ADA guidelines is:
a) HbA1a
b) HbA2
c) HbA1b
d) HbA1c - Which substance, when present in increased concentrations, can inhibit chromogen production in the glucose oxidase (peroxidase) method?
a) Bilirubin
b) Ascorbic Acid
c) Uric Acid
d) Hemoglobin - The most frequent cause of galactosemia is a deficiency in which enzyme?
a) Glucose-6-Phosphatase
b) Galactokinase
c) Galactose-1-Phosphate Uridyl Transferase
d) Uridine Diphosphate 4 Epimerase - Serum levels that define hypoglycemia in preterm or low birth weight infants are:
a) The same as adults
b) Lower than adults
c) The same as a normal full-term infant
d) Higher than a normal full-term infant - If a fasting glucose is 90 mg/dL, which 2-hour postprandial glucose result most closely represents normal glucose metabolism?
a) 55 mg/dL (3.0 mmol/L)
b) 100 mg/dL (5.5 mmol/L)
c) 180 mg/dL (9.9 mmol/L)
d) 260 mg/dL (14.3 mmol/L) - In using ion-exchange chromatographic methods, falsely increased levels of HbA1c might be demonstrated in the presence of:
a) Iron Deficiency Anemia
b) Hemoglobin S (HbS)
c) Pernicious Anemia
d) Thalassemias - Which of the following serum constituents is most unstable if a blood specimen is left standing at room temperature for 8 hours before processing?
a) Cholesterol
b) Triglyceride
c) Creatinine
d) Glucose - After strenuous aerobic exercise, which combination of lactic acid and pyruvate levels would be most consistent in a post-exercise blood sample?
a) Normal lactic acid, low pyruvate
b) Low lactic acid, elevated pyruvate
c) Elevated lactic acid, low pyruvate
d) Elevated lactic acid, elevated pyruvate - A patient has a fasting serum glucose of 95 mg/dL and a 2-hour postprandial glucose of 105 mg/dL. The fasting glucose is best described as:
a) Normal; reflecting glycogen breakdown by the liver.
b) Normal; reflecting glycogen breakdown by skeletal muscle.
c) Abnormal; indicating diabetes mellitus.
d) Abnormal; indicating hypoglycemia.
- Which of the following is the basic unit of carbohydrates?
a) Monosaccharide
b) Disaccharide
c) Polysaccharide
d) Glycoprotein - Glucose, galactose, and fructose are examples of:
a) Amino acids
b) Monosaccharides
c) Disaccharides
d) Ketones - The process by which glucose is broken down to pyruvate is known as:
a) Gluconeogenesis
b) Glycogenesis
c) Glycolysis
d) Glycogenolysis - The main storage form of carbohydrate in the human body is:
a) Glucose
b) Sucrose
c) Glycogen
d) Cellulose - The enzyme hexokinase catalyzes the conversion of:
a) Glucose to fructose
b) Glucose to glucose-6-phosphate
c) Glucose-6-phosphate to pyruvate
d) Glucose to glycogen - Which of the following hormones lowers blood glucose levels?
a) Glucagon
b) Cortisol
c) Insulin
d) Epinephrine - The primary organ responsible for glucose storage and release is the:
a) Pancreas
b) Liver
c) Kidney
d) Spleen - The Embden–Meyerhof pathway is another name for:
a) Gluconeogenesis
b) Glycolysis
c) Glycogenolysis
d) Pentose phosphate pathway - The final product of aerobic glycolysis is:
a) Lactate
b) Pyruvate
c) Acetyl-CoA
d) Carbon dioxide - During anaerobic glycolysis, pyruvate is converted to:
a) Acetyl-CoA
b) Lactate
c) Citrate
d) Oxaloacetate - Which of the following hormones increases blood glucose levels?
a) Insulin
b) Estrogen
c) Glucagon
d) Oxytocin - The process of glycogen breakdown into glucose is called:
a) Glycogenesis
b) Glycogenolysis
c) Gluconeogenesis
d) Glycolysis - Which tissue depends almost entirely on glucose for its energy source?
a) Skeletal muscle
b) Brain
c) Liver
d) Kidney - Gluconeogenesis primarily occurs in the:
a) Brain
b) Liver
c) Skeletal muscle
d) Pancreas - The main purpose of gluconeogenesis is to:
a) Convert glucose to glycogen
b) Produce glucose from non-carbohydrate sources
c) Produce pyruvate from glucose
d) Convert glycogen to glucose - Which coenzyme is essential in glycolysis?
a) NAD⁺
b) FAD
c) CoA
d) ATP - The pentose phosphate pathway is important for the production of:
a) NADPH and ribose-5-phosphate
b) ATP and pyruvate
c) Lactate and NAD⁺
d) GTP and glucose-1-phosphate - Which of the following is the rate-limiting enzyme of glycolysis?
a) Hexokinase
b) Phosphofructokinase
c) Pyruvate kinase
d) Glucose-6-phosphate dehydrogenase - In which cellular organelle does glycolysis occur?
a) Nucleus
b) Cytoplasm
c) Mitochondria
d) Endoplasmic reticulum - The conversion of glucose-6-phosphate to glucose occurs in:
a) Muscle cells
b) Liver cells
c) Red blood cells
d) Adipose tissue - Diabetes mellitus is primarily a disorder of:
a) Protein metabolism
b) Lipid metabolism
c) Carbohydrate metabolism
d) Mineral metabolism - The normal fasting blood glucose level (mg/dL) is approximately:
a) 40–70
b) 70–110
c) 120–160
d) 160–200 - Which enzyme catalyzes the conversion of glucose to glucose-6-phosphate in the liver?
a) Hexokinase
b) Glucokinase
c) Phosphatase
d) Aldolase - Glycogen synthase is involved in which process?
a) Glycogenolysis
b) Glycogenesis
c) Gluconeogenesis
d) Glycolysis - A deficiency of glucose-6-phosphatase leads to which disorder?
a) Diabetes insipidus
b) Von Gierke’s disease
c) Addison’s disease
d) Maple syrup urine disease - The glucose tolerance test (GTT) is primarily used to evaluate:
a) Liver enzyme activity
b) Insulin function
c) Kidney function
d) Lipid metabolism - The glycosylated hemoglobin test (HbA1c) reflects:
a) Short-term glucose fluctuations
b) Average glucose control over 2–3 months
c) Renal glucose excretion
d) Daily fasting glucose variation - The enzyme glucose oxidase is used in laboratory measurement of:
a) Glycogen
b) Glucose
c) Urea
d) Lactate - Which of the following hormones is not directly involved in glucose regulation?
a) Insulin
b) Glucagon
c) Thyroxine
d) Oxytocin - The first step in glycolysis involves:
a) Oxidation of glucose
b) Phosphorylation of glucose
c) Reduction of NAD⁺
d) Formation of ATP
📌 How to Use This Practice Set
- Answer each question before checking the key.
- Focus on why the correct answer is right and the others are wrong.
- Use this set as timed practice to simulate the real exam environment.
Answer Key
Answer Key:
- c) ≤55 mg/dL (≤3.0 mmol/L)
- d) Glycolysis
- b) 50 mg/dL (2.3 mmol/L)
- c) 126 mg/dL (6.9 mmol/L)
- d) HbA1c
- c) To minimize glycolysis by cells or bacteria
- d) Glucagon
- b) It is approximately 1-5 mg/dL higher
- c) Inhibit glycolysis by white blood cells
- d) 200 mg/dL (11.0 mmol/L)
- d) Hexokinase
- a) A decrease in the glycated Hb value
- c) Average blood glucose levels of the past 2-3 months
- b) Fats
- c) H2 Breath Test
- c) The true glucose concentration is a function of the hematocrit.
- c) Draw a blood sample for glucose and then discontinue the test.
- c) Hematocrit
- c) A high carbohydrate diet for 3 days
- b) The NADH produced from the reduction of NAD.
- d) Glucose Tolerance Test
- d) HbA1c
- d) Hemoglobin
- c) Galactose-1-Phosphate Uridyl Transferase
- b) Lower than adults
- b) 100 mg/dL (5.5 mmol/L)
- b) Hemoglobin S (HbS)
- d) Glucose
- d) Elevated lactic acid, elevated pyruvate
- a) Normal; reflecting glycogen breakdown by the liver.
- a) Monosaccharide
- b) Monosaccharides
- c) Glycolysis
- c) Glycogen
- b) Glucose to glucose-6-phosphate
- c) Insulin
- b) Liver
- b) Glycolysis
- b) Pyruvate
- b) Lactate
- c) Glucagon
- b) Glycogenolysis
- b) Brain
- b) Liver
- b) Produce glucose from non-carbohydrate sources
- a) NAD⁺
- a) NADPH and ribose-5-phosphate
- b) Phosphofructokinase
- b) Cytoplasm
- b) Liver cells
- c) Carbohydrate metabolism
- b) 70–110
- b) Glucokinase
- b) Glycogenesis
- b) Von Gierke’s disease
- b) Insulin function
- b) Average glucose control over 2–3 months
- b) Glucose
- d) Oxytocin
- b) Phosphorylation of glucose
Top 8 Medical Laboratory Scientist (MLS) Exams:
Top 8 Medical Laboratory Scientist (MLS) Exams that are recognized globally and can help professionals validate their credentials and enhance their career opportunities:
1. ASCP – American Society for Clinical Pathology (USA)
- Exam Name: MLS(ASCP)
- Eligibility: Bachelor’s degree with clinical laboratory experience.
- Global Recognition: High
- Purpose: Certifies Medical Laboratory Scientists in the United States and internationally.
2. AMT – American Medical Technologists (USA)
- Exam Name: MLT(AMT) or MT(AMT)
- Eligibility: Academic and/or work experience in medical laboratory technology.
- Global Recognition: Moderate
- Purpose: Credentialing for medical technologists and technicians.
3. AIMS – Australian Institute of Medical and Clinical Scientists
- Exam Name: AIMS Certification Exam
- Eligibility: Assessment of qualifications and work experience.
- Recognition: Required for practice in Australia.
- Purpose: Certification and registration in Australia.
4. CSMLS – Canadian Society for Medical Laboratory Science
- Exam Name: CSMLS General or Subject-specific Exams
- Eligibility: Graduation from a CSMLS-accredited program or equivalent.
- Recognition: Canada
- Purpose: Entry-to-practice certification in Canada.
5. IBMS – Institute of Biomedical Science (UK)
- Exam Name: Registration and Specialist Portfolio Assessment
- Eligibility: Accredited degree and lab experience.
- Recognition: UK and some Commonwealth countries.
- Purpose: Biomedical Scientist registration with the HCPC (UK).
6. HAAD / DOH – Department of Health, Abu Dhabi (UAE)
- Exam Name: DOH/HAAD License Exam
- Eligibility: Degree in medical laboratory science and experience.
- Recognition: UAE (Abu Dhabi)
- Purpose: Licensure for medical laboratory practice in Abu Dhabi.
7. DHA – Dubai Health Authority (UAE)
- Exam Name: DHA License Exam for Medical Laboratory Technologists
- Eligibility: Relevant degree and experience.
- Recognition: Dubai, UAE
- Purpose: Professional license for clinical laboratory practice in Dubai.
8. MOH – Ministry of Health (Gulf Countries like UAE, Saudi Arabia, Kuwait)
- Exam Name: MOH License Exam
- Eligibility: BSc/Diploma in Medical Laboratory + experience.
- Recognition: Varies by country.
- Purpose: Required for practicing in public and private sector labs.
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