Clinical Biochemistry — MCQs

Clinical Biochemistry Indian Medical PG Practice Questions and MCQs

Question 291: Identify the false statement about bilirubin.

A. Bilirubin is taken up across the sinusoidal (basolateral) membrane of hepatocytes by a carrier-mediated mechanism
B. Conjugated bilirubin is then directed primarily toward the canalicular (apical) membrane
C. Conjugated bilirubin is primarily reabsorbed back into the bloodstream from the intestines
D. Bilirubin circulates in plasma by covalently binding to albumin (Correct Answer)

Explanation: ***Bilirubin circulates in plasma by covalently binding to albumin*** - This is the **FALSE** statement and the correct answer. - Bilirubin circulates in plasma predominantly bound to **albumin**, but this binding is **non-covalent**, not covalent. - This non-covalent binding allows for the release of bilirubin at the hepatocyte surface for uptake. *Bilirubin is taken up across the sinusoidal (basolateral) membrane of hepatocytes by a carrier-mediated mechanism* - This statement is **TRUE**; **unconjugated bilirubin** uptake by hepatocytes from the blood is facilitated by specific **carrier proteins** on the sinusoidal membrane, such as OATPs (organic anion transporting polypeptides). - This active transport mechanism ensures efficient clearance of bilirubin from circulation. *Conjugated bilirubin is then directed primarily toward the canalicular (apical) membrane* - This statement is **TRUE**; after conjugation in the hepatocyte, **conjugated bilirubin** is actively transported across the **canalicular (apical) membrane** into the bile canaliculi. - This process is mediated by transporters like MRP2 (multidrug resistance-associated protein 2), essential for bile formation and excretion. *Conjugated bilirubin is primarily reabsorbed back into the bloodstream from the intestines* - This statement is **TRUE** in the sense that it's not the most clearly false option, though it requires clarification. - **Conjugated bilirubin** is mostly excreted into the intestines via bile and is then converted by gut bacteria into **urobilinogen**. - A small fraction of urobilinogen (not conjugated bilirubin itself) can be reabsorbed via the enterohepatic circulation, but the primary fate of conjugated bilirubin is conversion and fecal excretion as stercobilin.

Question 292: Which one of the following biochemical parameters is the most sensitive to detect open spina bifida?

A. Maternal serum alpha fetoprotein.
B. Amniotic fluid alpha fetoprotein.
C. Amniotic fluid acetyl cholinesterase. (Correct Answer)
D. Amniotic fluid hexosaminidase.

Explanation: ***Amniotic fluid acetylcholinesterase*** - **Amniotic fluid acetylcholinesterase (AChE)** is highly specific and sensitive for detecting **open neural tube defects (NTDs)**, such as open spina bifida. - The enzyme leaks directly from the exposed neural tissue into the **amniotic fluid**, making its presence a strong indicator of the defect. *Maternal serum alpha fetoprotein* - **Maternal serum alpha-fetoprotein (MSAFP)** is a screening tool, but it is not as specific as amniotic fluid markers. - Elevated MSAFP can be caused by various other conditions, including **multiple gestations** or **abdominal wall defects**, leading to higher false-positive rates. *Amniotic fluid alpha fetoprotein* - While **amniotic fluid alpha-fetoprotein (AFAFP)** is elevated in open neural tube defects, it is less specific than **AChE**. - AFAFP can also be elevated in other conditions like **gastroschisis** or **omphalocele**, making AChE a more definitive diagnostic marker. *Amniotic fluid hexosaminidase* - **Hexosaminidase** is an enzyme that is elevated in conditions like **Tay-Sachs disease**, a lysosomal storage disorder. - It is **not used as a biochemical marker** for the detection of open spina bifida or other neural tube defects.

Question 293: What is the specific marker of neural tube defects?

A. Acetylcholinesterase (Correct Answer)
B. Inhibin A
C. Pregnancy-associated plasma protein A
D. Estriol

Explanation: ***Acetylcholinesterase*** - **Acetylcholinesterase (AChE)** is a **highly specific marker** for **open neural tube defects (NTDs)** when detected in amniotic fluid. - Its presence indicates direct leakage from exposed neural tissue due to incomplete closure of the neural tube. - **Clinical context**: While **AFP (alpha-fetoprotein)** is used for screening, **AChE is the specific confirmatory marker** that distinguishes open NTDs from other causes of elevated AFP. - AChE testing helps reduce false positives from AFP screening alone. *Inhibin A* - **Inhibin A** is a serum marker used in **prenatal screening** for aneuploidies, such as Down syndrome (trisomy 21). - It is typically **elevated in Down syndrome** during second-trimester screening. - Not a specific marker for neural tube defects. *Pregnancy-associated plasma protein A* - **Pregnancy-associated plasma protein A (PAPP-A)** is a serum marker used in **first-trimester screening** for chromosomal abnormalities like Down syndrome. - It is usually **decreased in Down syndrome** but has no direct association with neural tube defects. *Estriol* - **Unconjugated estriol (uE3)** is a serum marker used in **second-trimester prenatal screening** (quad screen). - It is typically **decreased in Down syndrome and Edward syndrome (trisomy 18)**, but not specifically indicative of neural tube defects.

Question 294: A destitute woman is admitted to the hospital with altered sensorium and dehydration; urine analysis shows mild proteinuria and no sugar; which test would be most appropriate to perform next to assess for possible ketosis?

A. Rothera's test (for ketone bodies) (Correct Answer)
B. Hays test (for bile salts)
C. Fouchet's test (for bile pigments)
D. Benedict's test (for reducing sugars)

Explanation: ***Rothera's test (for ketone bodies)*** - The patient's presentation with **altered sensorium** and **dehydration**, along with absent glycosuria, strongly suggests conditions like starvation ketosis or alcoholic ketoacidosis, making a test for ketones essential. - **Rothera's test** specifically detects **acetoacetate and acetone**, key indicators of ketosis, which are important in diagnosing metabolic emergencies. *Fouchet's test (for bile pigments)* - This test is used to detect **bile pigments (bilirubin)** in urine, indicating **jaundice** or liver dysfunction. - The patient's symptoms do not specifically point towards a need for bile pigment detection. *Hays test (for bile salts)* - **Hays test** uses sulfur powder to detect **bile salts** in urine as a floating test. - Bile salts in urine suggest cholestasis or obstructive jaundice, which is not indicated by the current clinical presentation. *Benedict's test (for reducing sugars)* - **Benedict's test** is used to detect **reducing sugars** (like glucose) in urine. - The urine analysis already reported **no sugar**, making this test redundant for the current clinical context.

Question 295: In the context of clinical biochemistry, which isoenzyme of lactate dehydrogenase (LDH) has the maximum electrophoretic mobility?

A. LDH-1 (Correct Answer)
B. LDH-5
C. LDH-2
D. LDH-3

Explanation: ***LDH-1*** - **LDH-1** is composed of four **H subunits** (HHHH) and is the most **anionic** form of lactate dehydrogenase. - Due to its high negative charge, it migrates fastest towards the **anode** during electrophoresis. *LDH-5* - **LDH-5** is composed of four **M subunits** (MMMM) and is the least **anionic** form. - It has the **lowest electrophoretic mobility**, migrating slowest towards the anode or even towards the cathode. *LDH-2* - **LDH-2** consists of three **H subunits** and one **M subunit** (HHHM). - It has the second-highest electrophoretic mobility, positioned after LDH-1. *LDH-3* - **LDH-3** is composed of two **H subunits** and two **M subunits** (HHMM). - Its electrophoretic mobility is intermediate, falling between LDH-2 and LDH-4.

Question 296: A 5-year-old child presents with symptoms of genu varum and wrist enlargement. Which one of the following biochemical measures would be most likely to be elevated in this patient?

A. Alkaline phosphatase (Correct Answer)
B. Calcium
C. Ferritin
D. Phosphorus

Explanation: ***Alkaline phosphatase*** - In **rickets**, which is characterized by **genu varum** (bowed legs) and **wrist enlargement**, there is defective bone mineralization. Osteoblasts attempt to compensate for this defect by producing more unmineralized osteoid, leading to increased activity and release of **alkaline phosphatase**. - **Alkaline phosphatase (ALP)** is a marker of **osteoblast activity** and bone formation, and its elevation reflects the body's attempt to lay down new bone, even if it's unmineralized. *Calcium* - In **nutritional rickets** (the most common form), **serum calcium levels** are often low or normal-to-low due to inadequate intake or absorption of calcium and vitamin D. - The body tries to maintain normal calcium levels through **secondary hyperparathyroidism**, which mobilizes calcium from bones but also further impairs mineralization. *Ferritin* - **Ferritin** is a protein that stores iron and is a marker for **iron stores** in the body. - Iron deficiency anemia is a separate condition and is not directly related to the bone deformities seen in rickets; therefore, ferritin would not typically be elevated in this context. *Phosphorus* - In **nutritional rickets**, **serum phosphorus levels** are typically low due to impaired intestinal absorption and increased renal excretion, often exacerbated by secondary hyperparathyroidism. - Phosphorus is crucial for bone mineralization, and low levels contribute to the pathogenesis of rickets.

Question 297: What is the freezing point of normal human plasma?

A. 0° C
B. –0.54° C (Correct Answer)
C. –1.54° C
D. 4° C

Explanation: ***–0.54° C*** - The **freezing point depression** of normal human plasma is approximately **–0.54° C**, which is a key physical property used to assess plasma osmolality. - This specific value reflects the **total concentration of solutes** (like electrolytes, glucose, and urea) in the plasma. *0° C* - This is the freezing point of **pure water**, which does not account for the dissolved solutes in human plasma. - Due to the presence of solutes, the freezing point of plasma is **depressed below 0° C**. *–1.54° C* - This value represents a significantly **lower freezing point depression**, suggesting a much higher concentration of solutes than found in normal human plasma. - Such a low freezing point would indicate a state of **severe hyperosmolality**. *4° C* - This temperature is above the freezing point of water and human plasma, typically used for **refrigeration** rather than indicating freezing point. - Plasma would be in a **liquid state** at this temperature.

Question 298: Which hemoglobin has diagnostic value in diabetes mellitus?

A. HbA
B. HbF
C. HbA1c (Correct Answer)
D. HbS

Explanation: ***HbA1c*** - **Glycated hemoglobin (HbA1c)** measures the average blood glucose levels over the past 2-3 months. - It is used to **diagnose diabetes mellitus**, monitor glycemic control, and assess the risk of complications. *HbA* - **Hemoglobin A (HbA)** is the most common adult hemoglobin, comprising about 95-98% of total hemoglobin. - It does not directly provide information about **long-term glycemic control**. *HbF* - **Fetal hemoglobin (HbF)** is the predominant hemoglobin during fetal life and declines after birth. - While persistence of HbF can affect HbA1c measurements (leading to falsely low values), it is **not used diagnostically for diabetes**. *HbS* - **Hemoglobin S (HbS)** is an abnormal hemoglobin variant responsible for **sickle cell anemia**. - It is crucial for diagnosing sickle cell disease but has **no diagnostic value for diabetes mellitus**.

Question 299: Which of the following statements about alpha-fetoprotein (AFP) is NOT true?

A. Decreased AFP levels are seen in Down syndrome
B. MSAFP is unrelated to the period of gestation (Correct Answer)
C. Diabetic patients have decreased AFP levels
D. AFP is produced by the fetal liver and yolk sac

Explanation: ***MSAFP is unrelated to the period of gestation*** - This is the correct answer because this statement is **NOT true** (i.e., it is FALSE). - **Maternal serum alpha-fetoprotein (MSAFP) levels are highly dependent on gestational age**, rising steadily during the second trimester and peaking around 15-18 weeks of gestation. - **Accurate gestational dating is crucial** for proper interpretation of MSAFP levels, as values must be adjusted for gestational age. *Decreased AFP levels are seen in Down syndrome* - This statement is **TRUE** and therefore not the answer to this "NOT true" question. - **Down syndrome (Trisomy 21)** is characterized by **decreased MSAFP levels**, along with increased hCG and decreased unconjugated estriol (the "triple screen"). - This biochemical pattern helps in prenatal screening for chromosomal abnormalities. *Diabetic patients have decreased AFP levels* - This statement is **TRUE** and therefore not the answer to this "NOT true" question. - **Diabetic patients**, especially those with pre-gestational diabetes, typically exhibit **decreased MSAFP levels**. - This reduction can be significant enough to mask neural tube defects even if present, making interpretation more challenging in diabetic pregnancies. *AFP is produced by the fetal liver and yolk sac* - This statement is **TRUE** and therefore not the answer to this "NOT true" question. - **Alpha-fetoprotein is synthesized primarily by the fetal liver and yolk sac** during fetal development. - It is the fetal equivalent of albumin and reaches maternal circulation through the placenta, which is why it can be measured in maternal serum.

Question 300: Which of the following biochemical markers is NOT elevated in a child presenting with jaundice, icterus, pruritus, and clay-colored stools?

A. Gamma glutamyl transpeptidase
B. Alkaline phosphatase
C. 5' nucleotidase
D. Glutamate dehydrogenase (Correct Answer)

Explanation: ***Glutamate dehydrogenase*** - **Glutamate dehydrogenase (GLDH)** is an enzyme primarily found in the mitochondria of hepatocytes and is a marker of **hepatocellular necrosis**. - In a presentation dominated by **cholestasis** (jaundice, pruritus, clay-colored stools), GLDH is typically not elevated; rather, enzymes indicative of bile duct obstruction would be. *Alkaline phosphatase* - **Alkaline phosphatase (ALP)** is an enzyme found in the bile duct epithelium and is significantly elevated in **cholestatic conditions**, such as bile duct obstruction. - Its presence in high levels is a strong indicator of an issue with bile flow. *Gamma glutamyl transpeptidase* - **Gamma-glutamyl transpeptidase (GGT)** is a microsomal enzyme found in liver cells and bile duct epithelium, with very high sensitivity for **cholestatic liver disease**. - Its elevation along with ALP helps confirm a cholestatic pattern of liver injury. *5' nucleotidase* - **5' nucleotidase (5'-NT)** is an enzyme found in the cell membranes of hepatocytes and bile duct cells. - It is considered a more **specific marker for cholestasis** than ALP, as it is not elevated in bone diseases or pregnancy.

Practice by Chapter

Liver Function Tests

Practice Questions

Kidney Function Tests

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Cardiac Markers and Enzymes

Practice Questions

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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