Clinical Biochemistry — MCQs

Clinical Biochemistry Indian Medical PG Practice Questions and MCQs

Question 281: Hay's sulfur test is used to detect which of the following?

A. Bile salts in urine (Correct Answer)
B. Reducing sugar in urine
C. Ketone bodies in urine
D. Urobilinogen in urine

Explanation: ***Bile salts in urine*** - Hay's sulfur test is a classic qualitative test used to detect the presence of **bile salts** in a urine sample. - Bile salts reduce the **surface tension** of urine, causing sulfur powder to sink when sprinkled on the surface. *Reducing sugar in urine* - Reducing sugars (like glucose) are typically detected using tests such as **Benedict's test** or glucose oxidase strips, not Hay's sulfur test. - These tests rely on color changes due to the **reduction of copper ions** or enzymatic reactions, respectively. *Ketone bodies in urine* - Ketone bodies (acetoacetate, beta-hydroxybutyrate, acetone) are detected using tests like the **Rothera's test** or dipsticks, which react with acetoacetate. - These reactions produce color changes in the presence of ketones, unrelated to surface tension. *Urobilinogen in urine* - Urobilinogen in urine is commonly detected using **Ehrlich's reagent** (e.g., in a dipstick test) which forms a red color. - Elevated urobilinogen indicates issues with liver function or hemolysis, and its detection does not involve surface tension.

Question 282: What is the normal range of ferritin levels in adult males?

A. 30-300 ng/ml (Correct Answer)
B. 300-500 ng/ml
C. 10-20 ng/ml
D. 500-700 ng/ml

Explanation: ***30-300 ng/ml*** - The normal range for **ferritin levels** in adult males is typically **30-300 ng/ml** (some laboratories report 30-400 ng/ml). - Ferritin is an **iron storage protein**, and its levels reflect the body's iron stores. - Values below 30 ng/ml suggest **iron deficiency**, while values above 300 ng/ml may indicate iron overload or inflammatory conditions. *10-20 ng/ml* - These levels are **significantly low** and indicate **iron deficiency**. - This range is well below the normal threshold and would warrant investigation and likely iron supplementation. - Levels below 15 ng/ml are diagnostic of **iron deficiency** even in the absence of anemia. *300-500 ng/ml* - Levels in this range are considered **elevated** and can indicate iron overload, chronic inflammation, liver disease, or malignancy. - While some laboratories extend the upper limit to 400 ng/ml, persistent elevation above 300 ng/ml warrants further investigation. - Common causes include **hemochromatosis**, **chronic liver disease**, or **inflammatory conditions**. *500-700 ng/ml* - These levels are **significantly elevated** and strongly suggest **iron overload conditions** such as **hemochromatosis**, severe inflammatory states, or hepatocellular injury. - High ferritin levels can be associated with organ damage, leading to conditions like **cirrhosis** or **cardiomyopathy**. - Requires urgent investigation to identify the underlying cause.

Question 283: What is the unit for a prolactin level of 20 in blood?

A. ng/ml (Correct Answer)
B. mg/ml
C. mg/l
D. ng/l

Explanation: ***ng/ml*** - Prolactin levels in blood are typically measured in **nanograms per milliliter (ng/mL)**, reflecting the very small concentrations of hormones. - A value of 20 ng/mL falls within the typical reference range for prolactin. *mg/mL* - **Milligrams per milliliter (mg/mL)** is a unit used for much higher concentrations, more common for drugs or larger molecules, not hormones like prolactin. - If prolactin were measured in mg/mL, a value of 20 mg/mL would be an astronomically high and physiologically impossible level. *mg/L* - **Milligrams per liter (mg/L)** is also a unit for higher concentrations than those typically seen for hormones in blood. - 20 mg/L is equivalent to 20 µg/mL or 20,000 ng/mL, which would indicate severe hyperprolactinemia. *ng/L* - **Nanograms per liter (ng/L)** is a unit for extremely low concentrations. - A reading of 20 ng/L would be too low for normal physiological prolactin levels, as 1 ng/mL equals 1000 ng/L.

Question 284: Diagnosis of carcinoid tumour is done by urinary estimation of:

A. VMA
B. Metanephrines
C. Catecholamines
D. 5HIAA (Correct Answer)

Explanation: ***5HIAA*** - The urinary estimate of **5-hydroxyindoleacetic acid (5HIAA)** is the primary diagnostic test for **carcinoid tumors** [1], particularly those secreting serotonin. - Elevated levels of **5HIAA** in urine indicate excessive serotonin production, which is characteristic of these tumors. *VMA* - **Vanillylmandelic acid (VMA)** is a metabolite of catecholamines and is primarily used in diagnosing **neuroblastoma** or **pheochromocytoma**, not carcinoid tumors. - Although it indicates catecholamine secretion, it does not correlate with **serotonin** levels associated with carcinoid tumors. *Metanephrines* - **Metanephrines** represent metabolites of catecholamines and are mainly evaluated for **pheochromocytoma**. - They do not provide information on serotonin metabolism or carcinoid tumor activity. *Catecholamines* - Catecholamines such as **epinephrine and norepinephrine** are not specifically related to carcinoid tumors and often indicate other neuroendocrine tumors. - Their levels do not correlate with serotonin or its metabolite, **5HIAA**, used for carcinoid diagnosis. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 12-15.

Question 285: Which isoenzyme of lactate dehydrogenase (LDH) is predominantly elevated in liver injury?

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

Explanation: ***LDH-5 isoenzyme most significant in hepatic conditions*** - **LDH-5** is the predominant isoenzyme found in the **liver** and skeletal muscle. - An elevation of **LDH-5** is highly indicative of **hepatocellular damage** or injury. *LDH-1 isoenzyme associated with cardiac tissue* - **LDH-1** is primarily present in the **heart** and red blood cells. - Its elevation suggests conditions like **myocardial infarction** or hemolytic anemia, not liver injury. *LDH-3 isoenzyme typical in respiratory system* - **LDH-3** is found in the **lungs**, kidneys, and other tissues. - While it can be elevated in **pulmonary embolism** or renal disease, it is not specific for liver injury. *LDH-2 isoenzyme linked to erythrocyte metabolism* - **LDH-2** is abundant in **red blood cells** and also found in the heart and kidneys. - Elevations are often seen in conditions involving **hemolysis** or myocardial damage, similar to LDH-1.

Question 286: What is the most sensitive biochemical marker for a 7-day old myocardial infarction?

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

Explanation: ***Troponin I/T*** - **Cardiac troponins (I and T)** are highly sensitive and specific biomarkers for **myocardial injury**. - While they rise quickly after an MI, they also remain elevated for an extended period, typically **7 to 10-14 days**, making them ideal for detecting a 7-day-old event. *CPK MB* - **Creatine phosphokinase MB (CPK-MB)** is a well-known cardiac marker, but its elevation is more transient, usually returning to normal within **2-3 days** post-MI. - Therefore, it would likely be undetectable or near baseline 7 days after the event, making it insensitive for this duration. *LDH* - **Lactate dehydrogenase (LDH)** used to be used as a cardiac marker, but it is **non-specific** and found in various tissues. - While it can remain elevated for an extended period after an MI (up to 10-14 days), its lack of specificity makes other markers, particularly troponins, much more reliable for confirming myocardial damage. *Myoglobin* - **Myoglobin** is one of the earliest markers to rise after myocardial injury, but it is also **rapidly cleared** from the bloodstream, usually within 24 hours. - Due to its short half-life, myoglobin would not be elevated 7 days after an MI, making it unsuitable for detecting such a remote event.

Question 287: Halitosis is primarily caused by:

A. Hydrogen sulfide (Correct Answer)
B. Collagenase enzymes
C. Trypsin-like enzymes
D. Alkaline phosphatase

Explanation: ***Hydrogen sulfide*** - Halitosis, or bad breath, is predominantly caused by **volatile sulfur compounds (VSCs)**, with **hydrogen sulfide (H₂S)** being a major contributor. - These VSCs are produced by gram-negative anaerobic bacteria, primarily in the oral cavity, during the breakdown of proteins. *Collagenase enzymes* - **Collagenase enzymes** are involved in the breakdown of collagen, a structural protein found in connective tissues. - While bacteria in the oral cavity produce collagenases, their primary role is in **tissue degradation** (e.g., in periodontal disease), not directly generating the malodor of halitosis. *Trypsin-like enzymes* - **Trypsin-like enzymes** are proteases that cleave peptide bonds after basic amino acids. - These enzymes are primarily associated with protein digestion in the gut and are not the main cause of the specific odorous compounds responsible for halitosis. *Alkaline phosphatase* - **Alkaline phosphatase** is an enzyme involved in dephosphorylating molecules and is elevated in various medical conditions. - It plays no direct role in the production of **volatile sulfur compounds** that cause halitosis.

Question 288: Which of the following flipped pattern of LDH is seen in myocardial infarction?

A. LDH 1>2 (Correct Answer)
B. LDH 5>4
C. LDH 3>4
D. LDH 2>1

Explanation: ***LDH 1>2*** - In **myocardial infarction**, the predominant **LDH isoenzyme** released from damaged heart muscle is **LDH-1**. - A **flipped pattern** where **LDH-1 activity exceeds LDH-2 activity** is highly characteristic of acute myocardial infarction. *LDH 3>4* - An increase in **LDH-3** is typically associated with conditions affecting the **lungs, lymph glands, pancreas, and spleen**, rather than acute cardiac events. - This pattern would not indicate specific cardiac damage as seen in myocardial infarction. *LDH 5>4* - Elevated **LDH-5** is usually indicative of **liver disease, skeletal muscle damage, or congestive heart failure**, distinguishing it from myocardial infarction. - This pattern specifically points to damage in tissues rich in the LDH-5 isoenzyme, not the heart. *LDH 2>1* - The **normal pattern** of LDH isoenzymes in healthy individuals is usually **LDH-2 > LDH-1**. - Therefore, this pattern would not suggest myocardial infarction, but rather a normal state or other conditions.

Question 289: Which enzyme is primarily evaluated for diagnosing myopathies?

A. Gamma-glutamyl transferase (GGT)
B. Creatine kinase (CK) (Correct Answer)
C. Lactic dehydrogenase (LDH)
D. Alanine aminotransferase (ALT)

Explanation: ***Creatine kinase (CK)*** - **Creatine kinase** is an enzyme found predominantly in **muscle cells** (skeletal and cardiac) and to a lesser extent in the brain. - Elevated levels in the blood are indicative of **muscle damage** or breakdown, making it the primary marker for diagnosing and monitoring myopathies. *Gamma-glutamyl transferase (GGT)* - GGT is an enzyme primarily found in the **liver** and **bile ducts**. - Elevated GGT levels are typically associated with **liver disease** or **bile duct obstruction**, not muscle disorders. *Lactic dehydrogenase (LDH)* - **Lactic dehydrogenase** is an enzyme found in many body tissues, including the heart, liver, kidneys, skeletal muscle, and red blood cells. - While LDH can be elevated in muscle damage, its lack of specificity to muscle makes it a less precise diagnostic indicator for myopathies compared to CK. *Alanine aminotransferase (ALT)* - **Alanine aminotransferase** is an enzyme found predominantly in the **liver**. - Elevated ALT levels are a key indicator of **hepatocellular damage** or liver disease, not primary muscle disorders.

Question 290: In which of the following conditions does the level of creatine kinase-1 increase?

A. Myocardial ischemia
B. Brain Ischemia (Correct Answer)
C. Kidney damage
D. Electrical cardioversion

Explanation: ***Brain Ischemia*** - **Creatine kinase-1 (CK-BB)**, or brain type CK, is predominantly found in the **brain**, gastrointestinal tract, and smooth muscle. - An increase in its level in the **serum** primarily indicates damage to the brain, such as following an **ischemic stroke** or severe head injury. *Myocardial ischemia* - **Myocardial ischemia** primarily causes an elevation in **creatine kinase-2 (CK-MB)**, the cardiac-specific isoform of creatine kinase. - While total CK may be elevated, **CK-MB** is the hallmark marker for cardiac muscle damage, not CK-BB. *Kidney damage* - **Kidney damage** is typically assessed by markers like **creatinine** and **blood urea nitrogen (BUN)**. - Creatine kinase isoforms are not specific indicators of kidney injury, although severe muscle damage (and thus CK elevation) can lead to secondary kidney problems like **rhabdomyolysis-induced acute kidney injury**. *Electrical cardioversion* - **Electrical cardioversion** can cause minor skeletal muscle damage and, less commonly, some myocardial stunning. - This typically leads to a transient increase in **creatine kinase-3 (CK-MM)**, the skeletal muscle isoform, or potentially CK-MB if there is minor myocardial injury, but not CK-BB.

Practice by Chapter

Liver Function Tests

Practice Questions

Kidney Function Tests

Practice Questions

Cardiac Markers and Enzymes

Practice Questions

Pancreatic Function Tests

Practice Questions

Glucose Tolerance Tests

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Lipid Profile and Cardiovascular Risk

Practice Questions

Tumor Markers

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Hormonal Assays and Interpretation

Practice Questions

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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