Molecular Diagnostics Quality Control — MCQs
For DNA test, liquid blood is preserved in:
Order of drawing blood in vacutainers should be in the following sequence to prevent contamination?
Which test is used for detecting gunshot residue?
What is the technique for accurate quantification of gene expression?
Best initial screening test to diagnose HIV infection
Which of the following statements is correct about Paroxysmal Nocturnal Hemoglobinuria (PNH)?
Molecular genetic testing is used to detect all of the following except?
Molecular genetic testing is used to detect all of the following except?
Which agency monitors air quality in India?
What is an X-ray artifact?
Molecular Diagnostics Quality Control Indian Medical PG Practice Questions and MCQs
Question 1: For DNA test, liquid blood is preserved in:
- A. Sodium fluoride
- B. Potassium oxalate
- C. Sodium citrate
- D. EDTA (Correct Answer)
Explanation: ***EDTA*** - Ethylenediaminetetraacetic acid (EDTA) is the preferred anticoagulant for DNA extraction because it **chelates metal ions** (like magnesium), which are cofactors for **DNases** (enzymes that degrade DNA). - By inhibiting DNases, EDTA effectively **preserves DNA integrity** in blood samples for genetic testing. *Sodium fluoride* - **Sodium fluoride** is primarily used as an antiglycolytic agent to preserve glucose in blood samples. - It does not specifically function to preserve DNA or inhibit DNA degradation significantly. *Potassium oxalate* - **Potassium oxalate** acts as an anticoagulant by precipitating calcium, but it is not optimal for long-term DNA preservation. - Its anticoagulant properties are less suitable for molecular testing compared to EDTA, and it doesn't protect DNA as effectively. *Sodium citrate* - **Sodium citrate** is an anticoagulant primarily used for coagulation studies (e.g., PT, PTT) by chelating calcium. - While it prevents clotting, it is **less effective than EDTA** in protecting DNA from degradation by DNases, making it a poorer choice for DNA banking.
Question 2: Order of drawing blood in vacutainers should be in the following sequence to prevent contamination?
- A. Grey, Blue, Red, Violet
- B. Blue, Red, Violet, Grey (Correct Answer)
- C. Blue, Violet, Red, Grey
- D. Red, Blue, Violet, Grey
Explanation: ***Blue, Red, Violet, Grey*** - This sequence follows the **CLSI (Clinical and Laboratory Standards Institute) order of draw** guidelines, which are critical for preventing **cross-contamination** between additives of different vacutainers. - The order starts with tubes for **coagulation studies** (blue top with sodium citrate), followed by serum tubes (red top), EDTA tubes (violet top for hematology), and finally glycolytic inhibitor tubes (grey top for glucose). - This prevents tissue thromboplastin contamination and anticoagulant carryover that could affect laboratory test results. *Grey, Blue, Red, Violet* - This order is incorrect as it places the **grey top tube** (containing fluoride/oxalate) first, which could contaminate subsequent tubes with its additives and affect tests. - The **blue top tube** for coagulation studies should come early in the sequence to minimize tissue thromboplastin contamination. *Blue, Violet, Red, Grey* - This sequence is incorrect because the **violet top tube** (EDTA) is placed before the **red top tube** (serum). - **EDTA contamination** can chelate calcium and other cations, interfering with chemistry tests performed on serum in the red top tube. *Red, Blue, Violet, Grey* - This order is incorrect as the **red top tube** is placed first, followed by the **blue top tube** (citrate). - The blue top tube should precede tubes with clot activators to **prevent tissue thromboplastin** from contaminating coagulation samples, which would lead to falsely shortened clotting times.
Question 3: Which test is used for detecting gunshot residue?
- A. Lie test for Firearm injury
- B. Neutron activation analysis for firearm use (Correct Answer)
- C. Toluidine blue test
- D. Benzidine test for blood stain
Explanation: ***Neutron activation analysis for firearm use*** - **Neutron activation analysis (NAA)** is a highly sensitive and reliable method for detecting specific elements characteristic of **gunshot residue (GSR)**, such as **barium**, **antimony**, and **lead**. - This technique works by irradiating samples with neutrons, causing them to emit gamma rays that are unique to each element, allowing for precise identification and quantification of GSR particles. *Lie test for Firearm injury* - A "lie test" typically refers to a **polygraph test**, which assesses physiological responses to detect deception, not physical evidence like gunshot residue. - Polygraph tests are not used for identifying **firearm injury** or the presence of actual physical traces. *Toluidine blue test* - The **Toluidine blue test** is primarily used in dentistry to detect and delineate **dysplastic or malignant lesions** in the oral mucosa. - It has no application in the forensic analysis of gunshot residue or firearm use. *Benzidine test for blood stain* - The **Benzidine test** was historically used as a preliminary test for the presence of **blood stains**, as it reacts with the heme component of hemoglobin. - It is not used for detecting **gunshot residue** and has largely been replaced by safer and more specific tests due to its carcinogenic properties.
Question 4: What is the technique for accurate quantification of gene expression?
- A. PCR
- B. Real-Time Reverse Transcriptase PCR (Correct Answer)
- C. Reverse Transcriptase PCR
- D. Northern blot
Explanation: ***Real-Time Reverse Transcriptase PCR*** - This technique allows for the **quantification of gene expression** by concurrently reverse-transcribing RNA to cDNA and amplifying it while monitoring the accumulation of DNA in real-time using fluorescent reporters. - The ** threshold cycle (Ct) value** is inversely proportional to the initial amount of target mRNA, enabling precise quantification. *Northern blot* - This method is used to detect **RNA sequences** and can provide semi-quantitative data about gene expression levels based on band intensity. - However, it is generally **less sensitive** and provides less precise quantification compared to real-time PCR. *PCR* - **Standard PCR** amplifies DNA, but it is not directly used for gene expression quantification as it starts with DNA templates. - While it can be used to detect the presence of a gene, it does not quantify its expression without further modifications or additional steps like reverse transcription and real-time monitoring. *Reverse Transcriptase PCR* - This technique involves **reverse transcribing RNA into cDNA** and then performing standard PCR to amplify the cDNA. - While it confirms the presence of mRNA and allows for cDNA amplification, it is a **qualitative or semi-quantitative** method for expression, as the endpoint detection does not accurately reflect initial mRNA concentration due to plateau effects.
Question 5: Best initial screening test to diagnose HIV infection
- A. Complement fixation test
- B. Western blot
- C. ELISA (Correct Answer)
- D. RIA
Explanation: ***ELISA*** - **ELISA** (Enzyme-linked immunosorbent assay) is the most widely used and recommended initial screening test for HIV due to its high **sensitivity** and relative affordability [1]. - It detects **HIV antibodies** and/or **p24 antigen**, allowing for early detection of infection [1], [2]. *Complement fixation test* - The complement fixation test is a serological method used to detect antibodies or antigens, but it is **not commonly used** for HIV screening. - It has **lower sensitivity** and **specificity** for HIV compared to modern assays like ELISA. *Western blot* - The **Western blot** is a highly specific test used as a **confirmatory test** for HIV, not an initial screening test due to its complexity and cost [1], [2]. - It detects specific HIV proteins, used to confirm a positive ELISA result [2]. *RIA* - **Radioimmunoassay (RIA)** is a sensitive technique used to measure antigen or antibody concentrations, but it is **not the primary screening test** for HIV. - RIA involves **radioactive isotopes**, which pose logistical and safety challenges, making it less practical for routine screening compared to ELISA.
Question 6: Which of the following statements is correct about Paroxysmal Nocturnal Hemoglobinuria (PNH)?
- A. Sucrose lysis test is used for the confirmation
- B. Flow cytometry is the best investigation (Correct Answer)
- C. The most common cause of death is heart failure
- D. It is an inherited disorder
Explanation: ***Flow cytometry is the best investigation*** - **Flow cytometry** is the gold standard for diagnosing PNH as it directly detects the absence of **GPI-anchored proteins (CD55 and CD59)** on the surface of red blood cells, granulocytes, and monocytes. - This method is highly sensitive and specific, allowing for the precise quantification of PNH clones even when present in small numbers. *Sucrose lysis test is used for the confirmation* - The **sucrose lysis test** (or sugar-water test) was an older screening test for PNH, but it is **not specific or sensitive enough** for confirmation. - It works by inducing complement activation on PNH cells in low ionic strength sucrose solution [1], but it has a high rate of false positives and negatives. *The most common cause of death is heart failure* - The most common cause of death in patients with PNH is **thrombosis**, particularly in unusual sites such as hepatic, cerebral, or abdominal veins, due to the prothrombotic state caused by the disease. - While heart complications can occur, they are not the leading cause of mortality. *It is an inherited disorder* - PNH is an **acquired clonal disorder** of hematopoietic stem cells, not an inherited genetic disorder [1]. - It results from a somatic mutation in the **PIG-A gene** in a hematopoietic stem cell, leading to the deficiency of GPI-anchored proteins.
Question 7: Molecular genetic testing is used to detect all of the following except?
- A. Translocation (Correct Answer)
- B. Point mutation
- C. Amplification
- D. Deletion
Explanation: ***Translocation*** - This is the **intended answer** for this question, based on a distinction between traditional molecular genetic testing and cytogenetic methods. - Historically, **large-scale chromosomal translocations** were primarily identified by **conventional cytogenetic methods** like **karyotyping**. - However, in modern practice, translocations **can be detected** by molecular techniques including **FISH (fluorescence in situ hybridization)**, **RT-PCR** for specific fusion genes (e.g., BCR-ABL), and **next-generation sequencing** [3], [4]. - The distinction is becoming less clear as molecular cytogenetic techniques bridge both fields. *Point mutation* - **Single nucleotide changes** (point mutations) are the **classic target** of molecular genetic testing [1]. - Readily detected by **Sanger sequencing**, **next-generation sequencing**, **PCR-based methods**, and **allele-specific assays** [3]. - These tests specifically identify alterations in individual DNA bases. *Amplification* - **Gene amplifications** (increased copy number) are routinely detected using molecular genetic techniques. - Methods include **quantitative PCR (qPCR)**, **digital PCR**, **FISH**, and **array comparative genomic hybridization (aCGH)** [2]. - Example: HER2 amplification testing in breast cancer. *Deletion* - **Deletions** ranging from single nucleotides to whole genes are readily detectable by molecular genetic testing [1]. - Techniques include **multiplex ligation-dependent probe amplification (MLPA)**, **aCGH**, **next-generation sequencing**, and **deletion-specific PCR** [2], [3]. - Small and large deletions are both within the scope of modern molecular diagnostics [1], [3]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 183-184. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 186-187. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 185-186. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 342-343.
Question 8: Molecular genetic testing is used to detect all of the following except?
- A. Deletion
- B. Translocation (Correct Answer)
- C. Amplification
- D. Point mutation
Explanation: ***Translocation*** - **Translocations** are chromosomal rearrangements that were historically detected primarily by **cytogenetic methods** (karyotyping, conventional FISH), rather than by traditional molecular genetic testing methods focused on DNA sequencing [3]. - While modern molecular techniques like **RT-PCR for fusion transcripts** (e.g., BCR-ABL), **NGS-based fusion detection**, and **targeted breakpoint sequencing** can now detect translocations, the classic distinction is that translocations involve large-scale structural chromosomal changes better visualized by cytogenetics [2], [3]. - In the traditional classification, molecular genetic testing referred primarily to **sequence-based methods** (PCR, Sanger sequencing) that detect smaller-scale DNA changes rather than gross chromosomal rearrangements. *Deletion* - **Deletions** are readily detected by molecular genetic testing using PCR, Sanger sequencing, MLPA (Multiplex Ligation-dependent Probe Amplification), and NGS [5]. - These techniques identify missing DNA sequences by analyzing changes in fragment size, read depth, or absence of expected amplification products [2], [5]. *Amplification* - **Amplification** (increased gene copy number) is detected by molecular methods including **quantitative PCR (qPCR)**, **digital PCR**, and **NGS-based copy number analysis** [4]. - These techniques quantify gene copy numbers to identify amplifications like HER2 amplification in breast cancer. *Point mutation* - **Point mutations** are the primary target of classic molecular genetic testing [1]. - Detected by **Sanger sequencing**, **allele-specific PCR**, **NGS panels**, and other sequence-based methods that identify single nucleotide changes in DNA [1], [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, p. 185. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 185-186. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 342-343. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, p. 344. [5] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 183-184.
Question 9: Which agency monitors air quality in India?
- A. None of the above
- B. Central pollution control board (Correct Answer)
- C. Central air quality board
- D. Central public works dept
Explanation: ***Central pollution control board*** - The **Central Pollution Control Board (CPCB)** is responsible for setting standards and monitoring air quality across India. - It works under the **Ministry of Environment, Forest and Climate Change (MoEFCC)**. *Central air quality board* - There is **no specific agency** or board named "Central Air Quality Board" in India. - Air quality monitoring falls under the broader mandate of pollution control. *Central public works dept* - The **Central Public Works Department (CPWD)** is primarily involved in the construction and maintenance of government buildings and infrastructure. - It does **not have a mandate** for environmental monitoring like air quality. *None of the options* - This option is incorrect because the **Central Pollution Control Board** is the correct agency responsible for air quality monitoring. - There is a specific statutory organization fulfilling this role.
Question 10: What is an X-ray artifact?
- A. A radiographic finding that indicates disease pathology
- B. A normal anatomical structure visible on X-ray
- C. An image distortion produced when the patient moves during the X-ray procedure
- D. An unwanted image distortion that doesn't represent actual anatomy (Correct Answer)
Explanation: ***An unwanted image distortion that doesn't represent actual anatomy*** - An **X-ray artifact** is any feature or distortion on a radiographic image that is not present in the actual object being imaged. - These can arise from various sources such as patient movement, equipment malfunction, or improper technique, leading to **misinterpretation** of the image. - Artifacts are unwanted findings that can obscure true pathology or mimic disease. *A normal anatomical structure visible on X-ray* - This describes a **true anatomical finding**, which is the intended purpose of an X-ray. - Normal anatomical structures are expected and assist in diagnosis, unlike artifacts which obscure or mimic pathology. *An image distortion produced when the patient moves during the X-ray procedure* - While **patient motion** is a common cause of X-ray artifacts, this describes just one specific type (motion artifact), not a comprehensive definition of what an artifact is. - Other sources like metallic objects, scatter radiation, or detector issues can also cause artifacts. *A radiographic finding that indicates disease pathology* - This describes **true pathology** or disease findings, which is what radiologists aim to identify. - Artifacts are the opposite - they are false findings that do not represent actual anatomy or pathology.
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