Clinical Biochemistry Practice Questions

Q: Bone resorption markers are:

Urine total free deoxypyridinoline. ***Urine total free deoxypyridinoline*** - **Deoxypyridinoline (DPD)**, a collagen cross-link, is released during **collagen degradation** in bone resorption. - Its excretion in urine reflects the overall rate of **bone matrix breakdown**. *Free glutamic acid cross linkage* - This is not a recognized or specific **biomarker for bone resorption**. - **Glutamic acid** is an amino acid, and its cross-linkages are not typically associated with bone turnover markers. *Serum propeptide of type I procollagen* - This marker, specifically **P1NP (Procollagen Type I N-terminal Propeptide)**, is a **bone formation marker**, indicating new collagen synthesis. - It reflects the activity of **osteoblasts** in building bone, not osteoclasts in breaking it down. *Osteocalcin* - **Osteocalcin** is primarily a **bone formation marker**, produced by osteoblasts. - While it can be found in the blood, its levels generally correlate with **osteoblastic activity** and bone turnover, rather than solely bone resorption.

Q: Anticoagulant used to estimate glucose from a sample sent from PHC is:

Potassium oxalate + NaF. ***Potassium oxalate + NaF*** - **Potassium oxalate** acts as an anticoagulant, while **sodium fluoride (NaF)** inhibits glycolysis, preserving the glucose concentration in the sample over time, which is critical for samples transported from remote locations like PHCs. - This combination ensures accurate glucose estimation by preventing the consumption of glucose by blood cells during transit. *Sodium citrate* - **Sodium citrate** is commonly used for coagulation studies (e.g., PT, aPTT) as it binds **calcium ions**, preventing clot formation. - While it acts as an anticoagulant, it does not inhibit glycolysis, allowing blood cells to continue consuming glucose, leading to falsely low glucose readings over time. *EDTA* - **EDTA (ethylenediaminetetraacetic acid)** is a strong anticoagulant used primarily for **hematology studies** (e.g., CBC) as it preserves cell morphology. - It works by chelating **calcium ions**, but it does not prevent glycolysis, making it unsuitable for glucose estimation, especially if there's a delay in processing. *Calcium oxalate* - **Calcium oxalate** is not commonly used as an anticoagulant in clinical laboratories. - It has limited anticoagulant properties and does not inhibit glycolysis, making it inappropriate for glucose estimation.

Q: In which of the following cases does Benedict's test give a false positive?

Urine sample of patient with alkaptonuria. ***Urine sample of patient with alkaptonuria*** - In **alkaptonuria**, urine contains **homogentisic acid**, a strong reducing agent that reacts with Benedict's reagent, leading to a **false-positive** result for reducing sugars. - While it's a reducing substance, homogentisic acid is not a sugar, thus the positive Benedict's test is misleading in the context of glucose. *Urine sample of patient with classical galactosemia* - Patients with **classical galactosemia** excrete **galactose** in their urine, which is a reducing sugar and would give a **true positive** result with Benedict's test. - The presence of galactose in urine is a key diagnostic indicator for galactosemia and is correctly detected by Benedict's reagent. *Urine sample of 50 year old male with Type II DM* - A 50-year-old male with **Type II Diabetes Mellitus** would likely have **glucosuria** (glucose in urine) due to high blood glucose levels, leading to a **true positive** Benedict's test. - Glucose is a reducing sugar, and its presence in the urine correctly indicates hyperglycemia. *Urine sample of 10 year old child with Type I DM.* - A 10-year-old child with **Type I Diabetes Mellitus** would also exhibit **glucosuria** due to insulin deficiency, resulting in a **true positive** Benedict's test. - The Benedict's test would accurately detect the high levels of glucose excreted in the urine.

Q: Which of the following is abnormal constituent of urine:

Glucose. ***Glucose*** - The presence of **glucose** in urine (glucosuria) is abnormal and typically indicates that the blood glucose levels have exceeded the **renal threshold** for reabsorption (approximately 180 mg/dL). - This is commonly associated with conditions like **diabetes mellitus** or impaired renal tubular reabsorption. - Normally, glucose is completely reabsorbed in the proximal convoluted tubule, so its presence in urine is always pathological in adults. *Urea* - **Urea** is a normal and the most abundant nitrogenous waste product in urine, formed from the breakdown of proteins in the liver via the urea cycle. - Its presence is essential for the excretory function of the kidneys. - Normal excretion: 20-35 g/day. *Creatine* - **Creatine** should be distinguished from **creatinine** (its metabolic end-product, which is a normal constituent of urine). - In healthy adults, creatine is normally absent or present only in trace amounts in urine; significant creatinuria can occur in children, pregnant women, or individuals with conditions like muscular dystrophy or hyperthyroidism. - However, for this question, **glucose** is the clearly abnormal constituent as it should never be present in normal urine, whereas small amounts of creatine can be physiological in certain populations. *None of the options* - This option is incorrect because **glucose** is definitively an abnormal constituent of urine, indicating underlying pathology such as diabetes mellitus or renal glycosuria.

Q: Thyroxine binding globulin (TBG) is increased in:

Pregnancy. ***Pregnancy*** - Estrogen levels are elevated during **pregnancy**, which leads to an increase in the synthesis of **TBG** by the liver. - Increased TBG binds more thyroid hormone, reducing free thyroid hormone levels, which then stimulates the thyroid gland to produce more. *Cancer chemotherapy* - Many **chemotherapeutic agents** can damage the liver or interfere with protein synthesis, potentially leading to a *decrease* in TBG and other plasma proteins. - Chemotherapy can also induce **hypothyroidism** directly or indirectly, which may alter thyroid hormone binding. *Nephrotic syndrome* - **Nephrotic syndrome** is characterized by significant proteinuria, where plasma proteins, including **TBG**, are lost through the kidneys in the urine. - This leads to a *decrease* in serum TBG levels, which can affect total thyroid hormone measurements but typically does not cause overt thyroid dysfunction due to compensatory mechanisms. *Glucocorticoid therapy* - **Glucocorticoids** (e.g., prednisone, dexamethasone) are known to *decrease* the hepatic synthesis of **TBG**. - This reduction in TBG can lead to lower total thyroid hormone levels without necessarily indicating thyroid gland dysfunction, as free thyroid hormone levels often remain normal.

Q: Proper evaluation of serum calcium level requires estimation of:

Serum albumin. ***Serum albumin*** - Approximately **40-45% of total serum calcium** is bound to plasma proteins, primarily **albumin** - Changes in albumin levels (e.g., hypoalbuminemia) significantly affect total calcium measurements - A **correction formula** is essential: Corrected Ca = Measured Ca + 0.8 × (4.0 - measured albumin in g/dL) - This allows accurate estimation of the physiologically active **ionized calcium** level - Without albumin correction, hypocalcemia may be falsely diagnosed in hypoalbuminemic states *Incorrect: Urinary output* - While urinary calcium excretion is important for assessing calcium balance, urinary output itself is not directly used to evaluate serum calcium levels - It reflects renal function and fluid status, not calcium-protein binding *Incorrect: Serum phosphorus* - Serum phosphorus is important in calcium-phosphate homeostasis, particularly in kidney disease or parathyroid disorders - However, phosphorus levels do not directly influence calcium binding to albumin - Not required for correcting total serum calcium measurements *Incorrect: Serum potassium* - Serum potassium is a critical electrolyte but does not impact the interpretation or correction of serum calcium measurements - Potassium plays a role in nerve and muscle function, distinct from calcium homeostasis and protein binding

Q: Reye's syndrome is characterized by encephalopathy, fatty liver and the following biochemical changes except –

Hyperuricemia. ***Hyperuricemia*** - **Hyperuricemia** is not a typical characteristic of Reye's syndrome; instead, **elevated ammonia** is a key biochemical marker due to impaired urea cycle function. - The primary metabolic derangements in Reye's syndrome involve **mitochondrial dysfunction** affecting fatty acid oxidation and the urea cycle, rather than purine metabolism. *Moderate elevation of SGOT and SGPT* - Reye's syndrome is characterized by **moderate elevation** of aminotransferases (SGOT/AST and SGPT/ALT) due to **hepatic cellular damage** and **fatty infiltration**. - While other liver diseases can cause higher elevations, Reye's typically presents with this moderate increase reflecting widespread mitochondrial dysfunction. *Hypoglycemia* - **Hypoglycemia** is a common and dangerous feature of Reye's syndrome, particularly in children, due to **impaired gluconeogenesis** and **fatty acid oxidation** in the damaged liver. - The liver's inability to produce glucose from fat stores or other non-carbohydrate sources leads to critical drops in blood sugar levels. *Hypoglycorrhachia* - **Hypoglycorrhachia**, or low glucose concentration in the cerebrospinal fluid (CSF), is a significant finding in Reye's syndrome due to widespread **encephalopathy** and often reflects systemic hypoglycemia. - This low CSF glucose, coupled with neurological symptoms, contributes to the overall picture of brain dysfunction in the syndrome.

Q: Which is the best anticoagulant to send sample for plasma electrolyte measurement?

Lithium heparin. ***Lithium heparin*** - **Lithium heparin** is the anticoagulant of choice for serum electrolyte measurement because it does not interfere with the levels of most electrolytes. - It works by activating **antithrombin III**, which inhibits various coagulation factors, preventing clot formation without significantly altering ion concentrations. *Citrate* - **Citrate** binds to **calcium ions**, which are electrolytes. This will falsely decrease measured calcium levels. - It is primarily used for **coagulation studies** because of its calcium-chelating properties. *Sodium fluoride* - **Sodium fluoride** is primarily an **antiglycolytic agent** used in conjunction with an anticoagulant like potassium oxalate to preserve glucose levels. - It contains **sodium ions**, which would falsely elevate measured **sodium levels**. *EDTA* - **EDTA (ethylenediaminetetraacetic acid)** is a strong **chelating agent** that binds to various metal ions, including calcium and magnesium. - It would significantly lower measured **calcium** and **magnesium** levels and elevate **potassium levels** (if K2/K3 EDTA is used), making it unsuitable for electrolyte measurement.

Q: Biomarker of alcoholic hepatitis:

AST. ***Correct Option: AST (Aspartate Aminotransferase)*** - **Classic finding in alcoholic hepatitis**: AST:ALT ratio typically **>2:1** (often 2-3:1) - AST elevation is usually **moderate** (rarely >300 U/L) due to **pyridoxine (Vitamin B6) deficiency** in chronic alcoholics, which impairs ALT more than AST - **Mitochondrial AST** is released due to hepatocyte mitochondrial damage from alcohol toxicity - The AST predominance with relatively lower ALT is a **characteristic pattern** distinguishing alcoholic from non-alcoholic hepatitis *Incorrect Option: GGT (Gamma-Glutamyl Transferase)* - While **highly sensitive** for chronic alcohol consumption and often markedly elevated in alcoholic liver disease - **Not specific** for alcoholic hepatitis; elevated in various cholestatic and hepatobiliary conditions - Better marker for **screening alcohol abuse** and **monitoring abstinence** rather than diagnosing hepatitis *Incorrect Option: ALP (Alkaline Phosphatase)* - May be **mildly elevated** in alcoholic hepatitis, especially if cholestatic features present - **Less specific** and not a characteristic biomarker - More prominent in **cholestatic liver diseases** and bone disorders *Incorrect Option: LDH (Lactate Dehydrogenase)* - **Non-specific marker** of cellular injury, can be elevated in alcoholic hepatitis - Lacks specificity as it's elevated in numerous conditions (hemolysis, myocardial infarction, malignancy) - **Not diagnostically useful** for alcoholic hepatitis specifically

Q: Best investigation for metabolic disorders?

Tandem mass spectrometry. ***Tandem mass spectrometry*** - **Tandem mass spectrometry (MS/MS)** is the gold standard for newborn screening and diagnosis of many **inborn errors of metabolism** due to its ability to detect and quantify multiple metabolites simultaneously. - It allows for the rapid identification of abnormal levels of **amino acids**, **acylcarnitines**, and other metabolic markers in a single sample. *PCR* - **Polymerase Chain Reaction (PCR)** is primarily used for **amplifying DNA** or RNA sequences. - It is crucial for diagnosing **infectious diseases** or identifying genetic mutations, rather than directly measuring metabolites. *Western blot* - **Western blot** is a laboratory technique used to detect specific **proteins** in a sample. - It is valuable for assessing **protein expression** and identifying proteinopathies, but not for broad metabolic metabolite profiling. *Gel electrophoresis* - **Gel electrophoresis** is used to separate **macromolecules** like DNA, RNA, or proteins based on their size and charge. - While useful for analyzing biological molecules, it does not offer the sensitivity or specificity needed for routine **metabolite screening** in metabolic disorders.

Question 1

Bone resorption markers are:

Accepted Answer

Urine total free deoxypyridinoline

Answer

Free glutamic acid cross linkage.

Answer

Serum propeptide of type I procollagen

Answer

Osteocalcin

Question 2

Anticoagulant used to estimate glucose from a sample sent from PHC is:

Accepted Answer

Potassium oxalate + NaF

Answer

Sodium citrate

Answer

EDTA

Answer

Calcium oxalate

Question 3

In which of the following cases does Benedict's test give a false positive?

Accepted Answer

Urine sample of patient with alkaptonuria

Answer

Urine sample of patient with classical galactosemia

Answer

Urine sample of 50 year old male with Type II DM

Answer

Urine sample of 10 year old child with Type I DM.

Question 4

Which of the following is abnormal constituent of urine:

Accepted Answer

Glucose

Answer

Urea

Answer

Creatine

Answer

None of the options

Question 5

Thyroxine binding globulin (TBG) is increased in:

Accepted Answer

Pregnancy

Answer

Cancer chemotherapy

Answer

Nephrotic syndrome

Answer

Glucocorticoid therapy

Question 6

Proper evaluation of serum calcium level requires estimation of:

Accepted Answer

Serum albumin

Answer

Urinary output

Answer

Serum phosphorus

Answer

Serum potassium

Question 7

Reye's syndrome is characterized by encephalopathy, fatty liver and the following biochemical changes except –

Accepted Answer

Hyperuricemia

Answer

Moderate elevation of SGOT and SGPT

Answer

Hypoglycemia

Answer

Hypoglycorrhachia

Question 8

Which is the best anticoagulant to send sample for plasma electrolyte measurement?

Accepted Answer

Lithium heparin

Answer

Citrate

Answer

Sodium fluoride

Answer

EDTA

Question 9

Biomarker of alcoholic hepatitis:

Accepted Answer

AST

Answer

ALP

Answer

GGT

Answer

LDH

Question 10

Best investigation for metabolic disorders?

Accepted Answer

Tandem mass spectrometry

Answer

PCR

Answer

Western blot

Answer

Gel electrophoresis

Clinical Biochemistry — MCQs

Clinical Biochemistry — MCQs

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