Clinical Biochemistry — MCQs

Clinical Biochemistry Indian Medical PG Practice Questions and MCQs

Question 261: Which enzyme is typically elevated 4 to 6 hours after a myocardial infarction and returns to normal within 2 to 3 days?

A. CPK-MB (Correct Answer)
B. Troponin T
C. LDH
D. Myoglobin

Explanation: ***CPK-MB*** - **Creatine phosphokinase-MB (CPK-MB)** is a cardiac-specific enzyme that rises 4 to 6 hours after an MI, peaks at 18-24 hours, and typically returns to normal in **2 to 3 days** (48-72 hours). - Its presence confirms myocardial damage and helps in diagnosing **acute myocardial infarction**. *Troponin T* - **Troponin T** is a highly sensitive and specific cardiac marker, but it remains elevated for a longer period (up to **7-14 days**) after an MI, unlike the 2-3 day return to normal specified. - While it rises within 3-6 hours, its prolonged elevation makes it unsuitable for the given timeframe. *LDH* - **Lactate dehydrogenase (LDH)** is a non-specific marker that rises later (24-48 hours after MI) and remains elevated for a much longer duration (up to **10-14 days**), making it not fit the specified time course. - Its elevation can also be due to other conditions, such as **hemolytic anemia** or **liver disease**, reducing its diagnostic specificity for MI. *Myoglobin* - **Myoglobin** is one of the first markers to rise (within 1-4 hours) after an MI, but it is **not cardio-specific** and also returns to normal very quickly (within **12-24 hours**). - Its rapid return to normal is shorter than the 2-3 day timeframe specified in the question, and its lack of specificity means it can be elevated in muscle injury from other causes.

Question 262: A patient with jaundice has elevated levels of unconjugated bilirubin. Which phase of bilirubin metabolism is likely to be impaired?

A. Absorption
B. Conjugation (Correct Answer)
C. Excretion
D. Transport

Explanation: ***Conjugation*** - Elevated **unconjugated bilirubin** coupled with jaundice and dark urine suggests an impairment in the liver's ability to convert unconjugated bilirubin into its conjugated form. - This process, primarily mediated by **uridine diphosphate glucuronosyltransferase (UGT) enzymes**, is essential for bilirubin to become water-soluble and excretable. *Absorption* - **Bilirubin absorption** primarily occurs in the intestines for re-circulation (enterohepatic circulation) or in the liver from the bloodstream. Impaired absorption is not directly associated with a primary increase in unconjugated bilirubin in the blood. - Issues with absorption would likely manifest differently, possibly affecting the total bilirubin pool rather than specifically leading to an accumulation of its unconjugated form. *Excretion* - During **impaired excretion**, conjugated bilirubin would typically accumulate as it cannot be effectively transported out of the liver into the bile ducts or intestines. - While excretion ultimately affects overall bilirubin levels, a primary failure in excretion would lead to elevated **conjugated bilirubin**, not unconjugated. *Transport* - **Bilirubin transport** in the blood involves its binding to albumin to prevent its entry into tissues. Problems with transport might affect distribution but are not directly the primary cause of isolated elevated unconjugated bilirubin. - Impaired intrahepatic transport within hepatocytes could theoretically contribute, but the most direct and common cause of unconjugated hyperbilirubinemia is defective conjugation.

Question 263: Which biochemical marker would be most elevated in a patient with osteoporosis?

A. Alkaline phosphatase
B. N-terminal telopeptide (NTX) (Correct Answer)
C. C-terminal telopeptide (CTX)
D. Parathyroid hormone (PTH)

Explanation: ***N-terminal telopeptide (NTX)*** - **NTX** is a marker of **bone resorption**, reflecting the breakdown of type I collagen during bone turnover. - In osteoporosis, bone resorption exceeds bone formation, making **resorption markers like NTX the most elevated** biochemical markers. - NTX is widely used clinically to assess bone turnover and monitor treatment response in osteoporosis. - Elevated urinary or serum NTX indicates increased osteoclast activity and accelerated bone loss. *C-terminal telopeptide (CTX)* - **CTX** is also a bone resorption marker that measures collagen breakdown products. - Like NTX, it is elevated in osteoporosis, and both are considered equally valid markers of bone resorption. - CTX is often measured in serum and is also used to monitor osteoporosis treatment. - While CTX would also be significantly elevated, NTX and CTX are comparable markers of the same process. *Alkaline phosphatase* - **Alkaline phosphatase (ALP)**, particularly the bone-specific isoenzyme, reflects **osteoblast activity** and bone formation. - In **primary osteoporosis**, ALP levels are typically **normal or only mildly elevated**, as the problem is predominantly increased resorption. - Marked elevation of ALP suggests other bone disorders like **Paget's disease, osteomalacia, or active fracture healing**. *Parathyroid hormone (PTH)* - **PTH** is a regulatory hormone, not a bone turnover marker. - In primary osteoporosis, PTH levels are typically **normal**. - Elevated PTH suggests **secondary causes** such as primary hyperparathyroidism or vitamin D deficiency leading to secondary hyperparathyroidism. - PTH elevation would be a cause of osteoporosis rather than a marker of the disease itself.

Question 264: What is the clinical significance of measuring alkaline phosphatase (ALP) levels?

A. It indicates bone growth and liver function (Correct Answer)
B. It assesses renal function
C. It measures blood sugar control
D. It evaluates immune system activity

Explanation: ***It indicates bone growth and liver function*** - Elevated ALP levels often signify conditions affecting the **bones**, such as rapid growth in children, bone fractures, or bone diseases, as well as **liver conditions** like cholestasis or bile duct obstruction. - The enzyme is found in high concentrations in the liver, bile ducts, and bones, making it a valuable marker for disorders in these areas. *It assesses renal function* - **Renal function** is primarily assessed by measuring creatinine, urea, and glomerular filtration rate (GFR), not ALP levels. - While kidney disease can indirectly affect bone metabolism and thus ALP, ALP is not a direct marker for kidney function. *It measures blood sugar control* - **Blood sugar control** is primarily monitored through glucose, HbA1c, and insulin levels. - ALP is not directly involved in glucose metabolism or regulation, so it does not reflect blood sugar control. *It evaluates immune system activity* - **Immune system activity** is typically evaluated by measuring white blood cell counts, inflammatory markers (e.g., CRP, ESR), and specific antibody levels. - ALP levels do not directly indicate the state or activity of the immune system.

Question 265: Which biochemical marker is most indicative of a myocardial infarction?

A. Alanine transaminase
B. Aspartate transaminase
C. Alkaline phosphatase
D. Cardiac troponin I (Correct Answer)

Explanation: ***Cardiac troponin I*** - **Cardiac troponin I** is highly specific to cardiac muscle and is released into the bloodstream following myocardial cell injury. - Its presence at elevated levels is the **gold standard** for diagnosing a myocardial infarction and usually remains elevated for several days. *Alanine transaminase* - **Alanine transaminase (ALT)** is primarily an enzyme found in the liver and is a marker for **hepatic damage**. - While mild elevations can be seen in various conditions, it is not specific for cardiac injury. *Aspartate transaminase* - **Aspartate transaminase (AST)** is found in various tissues including the liver, heart, skeletal muscle, and kidneys. - Although it can be elevated after a MI, it is **not specific to cardiac injury** and can be elevated in liver disease, muscle damage, and hemolysis. *Alkaline phosphatase* - **Alkaline phosphatase (ALP)** is an enzyme primarily found in bone, liver, intestines, and placenta. - Elevated levels are typically associated with **liver disease (especially cholestatic)** or **bone disorders** and have no diagnostic significance for myocardial infarction.

Question 266: What is the significance of the 'Flipping effect' in clinical biochemistry?

A. LDH 1 > LDH 2 in myocardial infarction (Correct Answer)
B. LDH 2 > LDH 1 in liver disease
C. LDH 2 > LDH 3 in hemolysis
D. LDH 3 > LDH 2 in other conditions

Explanation: ***LDH 1 > LDH 2 in myocardial infarction*** - The "flipping effect" refers to the specific finding where **lactate dehydrogenase isoenzyme 1 (LDH 1)** levels become higher than **LDH 2** levels. - This inversion is a classic, though now less commonly used, indicator of **acute myocardial infarction (MI)** due to the release of cardiac LDH. *LDH 2 > LDH 1 in liver disease* - In healthy individuals, **LDH 2** is typically higher than **LDH 1**. - While liver disease can cause elevated total LDH, it primarily involves **LDH 5**, and does not typically present with the "flipping effect." *LDH 2 > LDH 3 in hemolysis* - **Hemolysis** primarily elevates **LDH 1** and **LDH 2**, as these isoenzymes are abundant in red blood cells. - The characteristic "flipping effect" specifically describes LDH 1 exceeding LDH 2, not LDH 2 exceeding LDH 3. *LDH 3 > LDH 2 in other conditions* - **LDH 3** is typically found in organs like the lung, kidney, pancreas, and spleen. - While its elevation can indicate pathology in these areas, it does not constitute the "flipping effect," which is defined by the specific ratio of **LDH 1** to **LDH 2**.

Question 267: Which of the following biochemical tests was traditionally used to diagnose Dubin Johnson syndrome?

A. Serum transaminases
B. Bromsulphalein test (BSP) (Correct Answer)
C. Hippurate test
D. Gamma glutamyl transferase level

Explanation: ***Bromsulphalein test (BSP)*** - The **Bromsulphalein (BSP) test** was traditionally used because patients with Dubin-Johnson syndrome exhibit a characteristic **secondary rise in plasma BSP** concentration, indicating impaired hepatic excretion of the dye. - This peculiar excretion pattern, with **re-release of conjugated BSP** from hepatocytes due to a defect in canalicular transport, was a diagnostic hallmark. *Serum transaminases* - **Serum transaminase levels** (ALT, AST) are typically normal in Dubin-Johnson syndrome, as it is a benign disorder of bilirubin transport, not hepatocyte injury. - Elevated transaminases would suggest **hepatocellular damage**, which is not the primary pathology in Dubin-Johnson. *Hippurate test* - The **hippurate test** measures hepatic conjugation and excretion capacity, primarily for benzoic acid, and is not specifically indicative of Dubin-Johnson syndrome. - This test is more often associated with overall **hepatic metabolic capacity** rather than specific transporter defects. *Gamma glutamyl transferase level* - **Gamma-glutamyl transferase (GGT)** levels are usually normal in Dubin-Johnson syndrome, as it is not a cholestatic or hepatobiliary obstructive disorder. - Elevated GGT typically points towards **biliary pathologies** or alcohol-related liver disease.

Question 268: What mediates oncogenic osteomalacia?

A. Phosphatonin (Correct Answer)
B. Calcitonin
C. Interleukin 2
D. Interleukin 6

Explanation: ***Phosphatonin*** - **Phosphatonin** is a general term for a group of phosphaturic hormones, with **FGF23 (fibroblast growth factor 23)** being the primary mediator of oncogenic osteomalacia. - Tumors produce excessive amounts of **FGF23**, leading to renal phosphate wasting and impaired vitamin D activation, which causes **osteomalacia**. *Calcitonin* - **Calcitonin** is a hormone produced by the parafollicular cells of the thyroid gland, primarily involved in **decreasing blood calcium levels** by inhibiting osteoclast activity and reducing renal calcium reabsorption. - It does not play a direct role in the pathogenesis of **oncogenic osteomalacia**, which is characterized by phosphate dysregulation. *Interleukin 2* - **Interleukin 2 (IL-2)** is a cytokine primarily involved in the **immune system**, promoting the growth and differentiation of T cells. - It is not directly implicated in **phosphate metabolism** or the development of oncogenic osteomalacia. *Interleukin 6* - **Interleukin 6 (IL-6)** is a cytokine with diverse roles in inflammation, immune response, and hematopoiesis. - While IL-6 can influence bone metabolism in other contexts (e.g., chronic inflammation), it is **not the direct mediator** of phosphate wasting seen in oncogenic osteomalacia.

Question 269: Which enzyme deficiency is associated with increased susceptibility to infections, including E. coli?

A. Lactase deficiency
B. Pepsin deficiency
C. Trypsin deficiency
D. Glucose-6-phosphate dehydrogenase (G6PD) deficiency (Correct Answer)

Explanation: ***Glucose-6-phosphate dehydrogenase (G6PD) deficiency*** - G6PD deficiency impairs the **pentose phosphate pathway**, reducing the production of **NADPH** in phagocytes. - Reduced **NADPH** leads to an inability to generate a robust **respiratory burst** required to kill pathogens like *E. coli*, thereby increasing susceptibility to infections. *Lactase deficiency* - This deficiency affects the digestion of **lactose**, leading to gastrointestinal symptoms such as bloating and diarrhea. - It does not directly impact the **immune system's ability to combat bacterial infections**. *Pepsin deficiency* - Pepsin is a gastric enzyme essential for **protein digestion** in the stomach. - While it can lead to impaired protein breakdown, it is not directly linked to an increased susceptibility to **bacterial infections** like *E. coli*. *Trypsin deficiency* - Trypsin is a pancreatic enzyme crucial for **protein digestion** in the small intestine. - Its deficiency affects nutrient absorption but does not directly compromise the **innate immune response** against bacteria.

Question 270: Which of the following is a synthetic oxygen carrier?

A. Chlorofluorocarbon
B. Perfluorocarbon (Correct Answer)
C. 1-fluoro-2,4-dinitrophenol
D. 2,4-dinitrophenol

Explanation: **Perfluorocarbon** - **Perfluorocarbons** (PFCs) are synthetic organic compounds that are chemically inert and can dissolve large amounts of gases, including oxygen. - Due to their ability to carry oxygen, PFCs have been investigated as **blood substitutes** and in drug delivery systems. *2,4-dinitrophenol* - **2,4-dinitrophenol** (DNP) is an **uncoupler of oxidative phosphorylation**, meaning it prevents ATP synthesis while electron transport continues, generating heat instead. - It is a metabolic poison and has been used as a weight-loss drug but is not an oxygen carrier. *Chlorofluorocarbon* - **Chlorofluorocarbons** (CFCs) are organic compounds containing carbon, chlorine, and fluorine, primarily known for their role as **refrigerants** and in **aerosol propellants**. - CFCs are environmentally harmful due to their impact on the ozone layer and do not function as oxygen carriers. *1-fluoro-2,4-dinitrophenol* - **1-fluoro-2,4-dinitrophenol** is a derivative of dinitrophenol and would likely share similar properties as an **uncoupler of oxidative phosphorylation**. - It is not recognized for its ability to carry oxygen.

Practice by Chapter

Liver Function Tests

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Kidney Function Tests

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Cardiac Markers and Enzymes

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Pancreatic Function Tests

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Glucose Tolerance Tests

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Lipid Profile and Cardiovascular Risk

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Tumor Markers

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Hormonal Assays and Interpretation

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Electrolytes and Acid-Base Balance Tests

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Cerebrospinal Fluid Analysis

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Point-of-Care Testing

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Quality Control in Clinical Biochemistry

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