Clinical Biochemistry — MCQs

Clinical Biochemistry Indian Medical PG Practice Questions and MCQs

Question 271: 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.

Question 272: Cataract in cases of diabetes mellitus is due to accumulation of ?

A. Calcified crystallins
B. Glycated fibrillins
C. Calcified fibrillins
D. Glycated crystallins (Correct Answer)

Explanation: ***Glycated crystallins*** - In diabetes, high glucose levels lead to **non-enzymatic glycation** of lens proteins, primarily **crystallins**. - Glycation causes aggregation and insolubilization of crystallins, leading to increased **light scattering** and cataract formation. - Additionally, the **polyol pathway** (glucose → sorbitol via aldose reductase) causes sorbitol accumulation in the lens, contributing to osmotic stress and protein damage. - Both glycation and sorbitol accumulation are key mechanisms in diabetic cataractogenesis. *Calcified crystallins* - While calcification can occur in some forms of cataracts (e.g., age-related, traumatic), it is **not the primary mechanism** for diabetic cataracts. - Diabetic cataracts are predominantly linked to **metabolic changes** (hyperglycemia-induced glycation and polyol pathway) rather than mineral deposition. *Glycated fibrillins* - **Fibrillin** is an extracellular matrix glycoprotein important for elastic fibers in connective tissues, but it is **not a major structural protein of the lens**. - The lens is composed primarily of **crystallins** (α, β, γ), not fibrillins. - Therefore, fibrillin glycation would not directly cause lens opacification. *Calcified fibrillins* - This option incorrectly identifies both the protein type and the mechanism. - **Fibrillin calcification** is not a known pathway for diabetic cataractogenesis. - Diabetic cataracts result from crystallin modifications, not fibrillin changes.

Question 273: Bilirubin in serum can be measured by

A. Ehrlich’s Reaction
B. Schlesinger’s Reaction
C. Fouchet's Reaction
D. Van den Bergh reaction (Correct Answer)

Explanation: ***Van den Bergh reaction*** - The **Van den Bergh reaction** is a common laboratory method used to quantify **bilirubin** in serum. - This method differentiates between direct (conjugated) and indirect (unconjugated) bilirubin using a **diazotized sulfanilic acid** reagent. *Ehrlich's Reaction* - **Ehrlich's reaction** is primarily used to detect **urobilinogen** in urine, not bilirubin in serum. - It involves the reaction of urobilinogen with **Ehrlich's reagent** (p-dimethylaminobenzaldehyde) to form a red color. *Schlesinger's Reaction* - **Schlesinger's reaction** is a test for the presence of **urobilin** in urine. - It uses a zinc salt, which reacts with urobilin to produce a characteristic **green fluorescence**. *Fouchet's Reaction* - **Fouchet's reagent** is used in urine analysis to detect the presence of **bilirubin** in a semi-quantitative manner, often indicating liver disease or biliary obstruction. - This reaction typically employs trichloroacetic acid and ferric chloride to produce a characteristic color change.

Question 274: In which condition is 5-Hydroxyindoleacetic acid (HIAA) elevated in urine?

A. Alkaptonuria
B. Albinism
C. Carcinoid (Correct Answer)
D. Phenylketonuria

Explanation: ***Carcinoid*** - **Carcinoid tumors** can synthesize and release large amounts of **serotonin**, which is metabolized in the body to **5-HIAA**. - Elevated **urinary 5-HIAA** is a key diagnostic marker for **carcinoid syndrome**, indicating excessive serotonin production. *Alkaptonuria* - This is a rare genetic disorder characterized by the accumulation of **homogentisic acid** in the body, leading to dark urine upon standing and ultimately **ochronosis**. - It does not involve abnormalities in serotonin metabolism or 5-HIAA levels. *Albinism* - Albinism is a group of inherited disorders characterized by very **little or no melanin pigment production**, commonly affecting the skin, hair, and eyes. - This condition is related to **tyrosine metabolism** and has no direct link to 5-HIAA levels. *Phenylketonuria* - **PKU** is a metabolic disorder caused by a deficiency in the enzyme **phenylalanine hydroxylase**, leading to a buildup of **phenylalanine** in the body. - This condition primarily affects phenylalanine metabolism and has no direct relationship with 5-HIAA levels, which are associated with serotonin metabolism.

Question 275: What is the estimated blood glucose level in mg/dL for a patient with an HbA1c of 8% based on the conversion formula?

A. 120
B. 160
C. 200 (Correct Answer)
D. 240

Explanation: ***200*** - The estimated average glucose (eAG) can be calculated from HbA1c using the formula: **eAG (mg/dL) = 28.7 × HbA1c (%) – 46.7**. - For an HbA1c of 8%, the calculation is: **28.7 × 8 – 46.7 = 229.6 – 46.7 = 182.9 mg/dL**, which is closest to 200 mg/dL among the given options. *120* - An eAG of 120-125 mg/dL would correspond to an **HbA1c between 5.8% and 6.0%**, which is below the given 8%. - This value typically reflects **well-controlled or pre-diabetic** blood glucose levels. *160* - An eAG of 160 mg/dL would correspond to an **HbA1c of approximately 7.0-7.2%**, which is lower than the given 8%. - This level is often the target for HbA1c in many **diabetic management guidelines**, but not for 8%. *240* - An eAG of 240 mg/dL would correspond to an **HbA1c of approximately 9.9%**, which is significantly higher than the given 8%. - This indicates **poorly controlled diabetes** and a much higher average blood glucose level.

Question 276: Which of the following is a positive acute phase protein that enhances the acute phase response?

A. Fibrinogen (Correct Answer)
B. Transferrin
C. Albumin
D. Prealbumin

Explanation: ***Fibrinogen*** - **Fibrinogen** is a key **positive acute phase protein** whose concentration increases significantly during inflammation - Its elevation contributes to the acute phase response by promoting **blood clotting** and influencing **erythrocyte sedimentation rate (ESR)** - Along with C-reactive protein (CRP), haptoglobin, and serum amyloid A, fibrinogen is among the major positive acute phase reactants *Transferrin* - **Transferrin** is a **negative acute phase protein**, meaning its concentration decreases during inflammation - This reduction is part of the body's iron-sequestration strategy to limit iron availability for invading pathogens - The decrease in transferrin helps restrict bacterial growth by reducing available iron *Albumin* - **Albumin** is a prominent **negative acute phase protein**, with its concentration decreasing during acute inflammation due to redistribution and reduced synthesis - It plays a vital role in maintaining **oncotic pressure** and transporting various substances - Its decline reflects the severity of inflammation and is used as a marker of the acute phase response *Prealbumin* - **Prealbumin** (also known as transthyretin) is a **negative acute phase protein** and a sensitive marker of nutritional status - Its rapid decline during inflammation makes it a useful indicator, as its synthesis is quickly reduced - It has a short half-life (2-3 days), making it more sensitive to acute changes than albumin

Question 277: Level of which of the following is not elevated in heart disease

A. SGOT
B. ALP
C. LDH
D. 5-nucleotidase (Correct Answer)

Explanation: ***5-nucleotidase*** - While other enzymes like LDH, SGOT, and ALP can be elevated in various conditions including heart disease (especially in the context of tissue damage), 5-nucleotidase is **not typically elevated in heart disease**. - Its elevation is more commonly associated with **biliary obstruction** or certain liver pathologies. *LDH* - **Lactate dehydrogenase (LDH)** is a marker of **cellular damage** and can be elevated in myocardial infarction, though it is less specific than troponins. - LDH levels rise later than CK-MB and remain elevated longer, indicating persistent tissue injury. *SGOT* - **Serum glutamic oxaloacetic transaminase (SGOT)**, also known as **aspartate aminotransferase (AST)**, is elevated in acute **myocardial infarction** due to cardiac muscle damage. - While it's a marker for cardiac injury, it's not specific as it's also highly concentrated in the liver. *ALP* - **Alkaline phosphatase (ALP)** can be mildly elevated in heart failure due to **hepatic congestion** caused by reduced cardiac output. - While its primary diagnostic significance is in bone and liver disease, its elevation in advanced heart disease is usually a secondary consequence.

Question 278: Converging point of both pathways in coagulation is at:

A. Factor VIII
B. Stuart factor X (Correct Answer)
C. Factor IX
D. Factor VII

Explanation: ***Stuart factor X*** [1][2] - It is the main **converging point** of the coagulation cascade, where both the intrinsic and extrinsic pathways meet to initiate the common pathway [1]. - Activated factor X leads to the conversion of **prothrombin to thrombin**, pivotal for clot formation [2]. *Factor VII* [2] - Primarily involved in the **extrinsic pathway** of coagulation, activating factor X, but does not serve as a converging point. - Its function is limited to starting the coagulation cascade, particularly upon tissue injury. *Factor IX* [2] - A key component of the **intrinsic pathway**, it leads to the activation of factor X but is not the point where both pathways converge. - It requires **factor VIII** for its activation, further illustrating its role within a specific pathway. *Factor VIII* - Also part of the **intrinsic pathway**, it acts as a cofactor for factor IX but does not integrate both pathways into a common point. - Its deficiency is associated with **Hemophilia A**, underscoring its specific pathway involvement. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Hemodynamic Disorders, Thromboembolic Disease, and Shock, pp. 128-130. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 582-583.

Question 279: Cystatin C levels are used for

A. Detecting UTI
B. Estimating GFR (Correct Answer)
C. Screening for Renal Ca
D. Estimating difference between CRF and ARF

Explanation: ***Estimating GFR*** - **Cystatin C** is a **proteinase inhibitor** produced by all nucleated cells at a constant rate, and its level in the blood is inversely related to the **glomerular filtration rate (GFR)**. - Unlike **creatinine**, Cystatin C levels are less affected by **muscle mass, diet, or inflammation**, making it a more reliable marker for early and subtle changes in GFR, especially in certain populations. *Detecting UTI* - **Urinary tract infections (UTIs)** are primarily detected through **urinalysis** (presence of **leukocytes, nitrites**, and **bacteria**) and **urine culture**. - **Cystatin C** is a serum marker for renal function and has no direct role in detecting the presence of bacterial infection in the urinary tract. *Estimating difference between CRF and ARF* - Differentiating between **chronic renal failure (CRF)** and **acute renal failure (ARF)** typically involves assessing the **chronicity of symptoms**, trend in **creatinine levels**, and **kidney size** and **echogenicity** on ultrasound. - While Cystatin C can reflect current GFR, it doesn't inherently provide discriminatory power between acute and chronic processes without serial measurements or additional clinical context. *Screening for Renal Ca* - **Renal cell carcinoma (RCC)** screening is primarily done using **imaging techniques** like **ultrasonography, CT, or MRI**, especially in individuals with risk factors or symptoms like **hematuria**. - **Cystatin C** is a marker of kidney function and does not serve as a tumor marker for renal cancer.

Question 280: Which of the following is not an acute phase reactant?

A. C-reactive protein
B. Haptoglobin
C. Endothelin (Correct Answer)
D. Fibrinogen

Explanation: ***Endothelin*** - Endothelin is a **vasoconstrictive peptide** primarily involved in regulating **blood vessel tone** and blood pressure. - While it plays a role in processes like inflammation and tissue repair, it is not synthesized or regulated in the same rapid, systemic manner as a classic acute phase reactant. *C-reactive protein* - **C-reactive protein (CRP)** is a rapidly responding acute phase reactant produced by the liver in response to **inflammation**, infection, and tissue injury. - Its levels can rise dramatically within hours of an inflammatory stimulus and are used as a marker for disease activity. *Haptoglobin* - **Haptoglobin** is an acute phase reactant that binds to free **hemoglobin** released from red blood cells during hemolysis, preventing oxidative damage. - Its levels typically increase during acute inflammation or infection, although it can also decrease with severe hemolysis. *Fibrinogen* - **Fibrinogen** is a critical acute phase protein involved in the **coagulation cascade** and wound healing. - Its concentration increases significantly during acute inflammation, contributing to the elevated **erythrocyte sedimentation rate (ESR)**.

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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