Evidence Collection and Preservation — MCQs
Disputed maternity can be solved by using the following tests, EXCEPT:
Certain obligations on the part of a doctor who undertakes a postmortem examination are the following, EXCEPT:
A nurse keeps the bins as shown in the image in the hospital ward. Which of the following items would go into the black bin?
A person with unsound mind can be released with pending investigation or trial under:-
Which of the following is the least suitable source for DNA extraction?
Amputated digits are preserved in:
During autopsy for virology study which agent is used for storing tissue:
What are the reasons a sample may be disqualified for culture?
The most specific test to detect blood stains is:
What is the most reliable method to determine the time of death within the first 24 hours after death?
Evidence Collection and Preservation Indian Medical PG Practice Questions and MCQs
Question 1: Disputed maternity can be solved by using the following tests, EXCEPT:
- A. Blood grouping
- B. HLA typing
- C. DNA fingerprinting
- D. Precipitin test (Correct Answer)
Explanation: ***Precipitin test*** - The **precipitin test** is used to determine the origin of a **blood sample**, specifically whether it is **human or animal blood**, by detecting species-specific proteins. It is not used for assessing maternity. - This test is primarily employed in **forensic serology** to differentiate between blood from different animal species, making it irrelevant for paternity or maternity disputes. *Blood grouping* - **Blood grouping** (e.g., ABO and Rh systems) can be used to **exclude paternity or maternity** by comparing the blood types of the child, mother, and alleged father. - If the child's blood type is incompatible with the alleged parents based on Mendelian inheritance, one or both can be excluded. *HLA typing* - **HLA typing** (Human Leukocyte Antigen) is a more powerful genetic marker system than ABO/Rh for determining paternity or maternity. - It involves analyzing highly polymorphic genes on chromosome 6 that encode cell surface proteins, providing a more definitive means of **inclusion or exclusion**. *DNA fingerprinting* - **DNA fingerprinting** (also known as **DNA profiling**) is the **most accurate and widely accepted method** for resolving paternity and maternity disputes. - It analyzes highly variable regions of DNA unique to each individual, providing a statistically strong basis for **inclusion or exclusion** by comparing genetic profiles.
Question 2: Certain obligations on the part of a doctor who undertakes a postmortem examination are the following, EXCEPT:
- A. Routinely record all positive findings and important negative ones
- B. He must keep the police informed about the findings (Correct Answer)
- C. The examination should be meticulous and complete
- D. He must preserve viscera and send for toxicology examination in case of poisoning
Explanation: ***He must keep the police informed about the findings*** - This is **NOT a formal obligation** of the doctor conducting a postmortem examination. - The doctor's primary duty is to conduct a thorough, objective examination and prepare a **formal postmortem report** that is submitted to the authority who requisitioned the examination (magistrate/police as per CrPC Section 174). - While findings may eventually reach the police through the official report, there is **no obligation to informally update or keep police informed** during the examination process. - The doctor's role is that of an **independent expert witness** to the court, not an investigative assistant to the police. - Maintaining independence and objectivity requires the doctor to document findings formally rather than providing ongoing informal updates to investigating officers. *Routinely record all positive findings and important negative ones* - This IS a **fundamental obligation** for any doctor performing a postmortem examination. - Both positive findings (pathological changes, injuries) and significant negative findings (absence of expected pathology) must be documented to provide a comprehensive and accurate record. - This meticulous documentation ensures the **integrity, reliability, and legal validity** of the postmortem examination and its conclusions. *The examination should be meticulous and complete* - This IS a **professional, ethical, and legal obligation** for any doctor undertaking a postmortem examination. - A systematic and thorough examination of all body systems is essential to accurately determine the cause of death and identify all relevant findings. - Incomplete examinations can lead to **missed diagnoses and miscarriage of justice** in medico-legal cases. *He must preserve viscera and send for toxicology examination in case of poisoning* - This IS a **crucial obligation** when poisoning is suspected or cannot be ruled out based on the postmortem findings. - Relevant viscera (liver, kidney, stomach contents) and bodily fluids (blood, urine) must be preserved in appropriate containers for subsequent toxicological analysis. - This step is **essential to confirm or exclude toxicological involvement** in the death and is a standard protocol in medico-legal postmortem examinations as per established guidelines.
Question 3: A nurse keeps the bins as shown in the image in the hospital ward. Which of the following items would go into the black bin?
- A. Gloves
- B. Soiled linen bedsheet
- C. Contaminated gloves
- D. Glove paper cover (Correct Answer)
Explanation: ***Glove paper cover*** - The black bin is typically designated for **general waste** that is neither infectious nor sharp. - A glove paper cover is considered **non-hazardous**, non-recyclable waste and would be appropriately disposed of in a black bin. *Gloves* - **Used gloves**, even if not obviously contaminated with bodily fluids, are considered potentially infectious waste and should not be placed in the black bin. - These should generally be disposed of in a **yellow bag or bin** (infectious waste) to prevent cross-contamination. *Soiled linen bedsheet* - A soiled linen bedsheet is considered **infectious waste**, as it may contain bodily fluids or pathogens. - This type of waste requires specific handling and disposal, usually in **red bags or bins**, not general waste. *Contaminated gloves* - **Contaminated gloves** are classified as infectious waste and must be disposed of in designated containers for biohazard materials. - Placing them in a black bin would pose a **risk of infection** to waste handlers and is against standard medical waste disposal protocols.
Question 4: A person with unsound mind can be released with pending investigation or trial under:-
- A. Section 84 Cr P C
- B. Section 328 Cr P C
- C. Section 330 Cr P C (Correct Answer)
- D. Section 84 IPC
Explanation: ***Section 330 Cr P C*** - This section specifically deals with the power of the Court to **release a person with unsound mind** (or other mental incapacitation) pending investigation or trial. - It allows for the release of such individuals on **sufficient security** being given that they will be properly taken care of and produced in Court when required. *Section 84 Cr P C* - **Section 84 CrPC** does not deal with the release of persons with unsound mind. - This option is a distractor that may confuse candidates with Section 84 IPC or other provisions. *Section 328 Cr P C* - This section deals with the **procedure** when an accused appears to be of unsound mind during an inquiry or trial before a Magistrate. - It focuses on stopping the proceedings and determining the accused's mental state, not directly on release pending investigation or trial. *Section 84 IPC* - This section of the Indian Penal Code (IPC) addresses the **acts of a person of unsound mind** and provides a defense against criminal liability. - It applies to the substantive criminal law regarding culpability, not the procedural aspects of release during investigation or trial.
Question 5: Which of the following is the least suitable source for DNA extraction?
- A. CSF (Correct Answer)
- B. Hair roots
- C. Semen
- D. Buccal mucosa
Explanation: ***CSF*** - **Cerebrospinal fluid (CSF)** contains a relatively **low number of cells**, making it a poor source for DNA extraction compared to other bodily fluids due to the scarcity of nuclear DNA. - While DNA can be extracted from CSF for specific diagnostic purposes (e.g., detection of pathogens), it is generally **not the preferred source** for DNA profiling or genetic studies due to the limited yield and potential for degradation. *Hair roots* - **Hair roots** (specifically the follicular tag) contain a significant number of **nucleated cells**, making them an excellent source for DNA extraction. - The DNA extracted from hair roots is often robust and sufficient for **forensic analysis** and genetic testing. *Semen* - **Semen** contains a high concentration of **sperm cells**, which are rich in nuclear DNA, making it a very good source for DNA extraction. - It is frequently used in **forensic investigations** and paternity testing due to its high DNA content. *Buccal mucosa* - **Buccal cells** scraped from the inside of the cheek provide a non-invasive and **abundant source of nucleated cells** for DNA extraction. - This method is widely used for genetic testing, **ancestry tracing**, and clinical diagnostics because of its ease of collection and high DNA yield.
Question 6: Amputated digits are preserved in:
- A. Plastic bag in ice (Correct Answer)
- B. Deep freezer
- C. Cold ringer lactate
- D. Cold saline
Explanation: ***Plastic bag in ice*** - The amputated digit should be placed in a **sterile plastic bag** and then immersed in a container with **ice water**. This method provides adequate cooling to preserve tissue viability without direct contact with ice, which can cause **frostbite**. - This approach slows down metabolic processes and reduces oxygen demand, extending the time window for successful **replantation**. *Deep freezer* - Placing an amputated digit directly into a deep freezer causes **ice crystal formation** within the cells, leading to severe **tissue damage** and making replantation impossible. - Extreme cold results in **cellular dehydration** and destruction, rendering the tissue non-viable for reattachment. *Cold ringer lactate* - While Ringer's lactate is an appropriate solution for **tissue irrigation** or to keep a digit moist in an emergency, it should not be used as the primary medium for prolonged preservation without adequate cooling. - For optimal preservation, Ringer's lactate could be used *inside* the plastic bag to bathe the digit, but the bag still needs to be placed on ice to achieve the necessary **hypothermic conditions**. *Cold saline* - Similar to Ringer's lactate, cold saline can be used to **cleanse** the amputated part or keep it moist temporarily. However, it is not ideal as the sole preservation method. - Direct immersion in saline with ice is better than plain saline at room temperature but still carries the risk of **tissue maceration** if not properly managed within a sealed bag on ice. The primary goal is cooling, not just hydration.
Question 7: During autopsy for virology study which agent is used for storing tissue:
- A. Alcohol
- B. Rectified spirit
- C. Sodium chloride
- D. 50% glycerine (Correct Answer)
Explanation: ***50% glycerine*** - **Glycerine** is commonly used for preserving tissues for virological studies because it helps to maintain viral viability by preventing **desiccation** and **denaturation** of viral particles. - It acts as a **cryoprotectant**, stabilizing cell membranes and protein structures, which is crucial for subsequent **viral isolation** and detection. *Alcohol* - **Alcohol** acts as a **fixative** by denaturing proteins and dehydrating tissues, which would inactivate most viruses and make them unsuitable for viability studies. - While useful for histopathology, it is not appropriate for preserving viral infectivity or integrity. *Rectified spirit* - **Rectified spirit** is a highly concentrated form of alcohol (typically 95% ethanol), and like alcohol, it causes **protein denaturation** and **dehydration**. - This property makes it unsuitable for preserving viral viability for subsequent virological studies. *Sodium chloride* - **Sodium chloride** alone in isotonic solutions can maintain tissue hydration but does not provide adequate **viral stabilization** or protection against degradation. - It would not prevent **enzymatic degradation** or maintain viral infectivity over time, especially at room temperature.
Question 8: What are the reasons a sample may be disqualified for culture?
- A. Sample brought within 2 hr of collection
- B. Sample brought in sterile plastic container
- C. Sample brought in formalin (Correct Answer)
- D. Sample obtained after cleaning the collection site
Explanation: ***Sample brought in formalin*** - Formalin is a **fixative** that will kill any viable **microorganisms** present in the sample, rendering it unsuitable for culture because no growth will occur. - The purpose of a culture is to identify living organisms; a fixed sample prevents this crucial step. *Sample brought within 2 hr of collection* - This is an **ideal scenario** for sample integrity, as it minimizes the time for degradation or overgrowth of contaminants. - **Prompt transport** ensures the viability of fastidious organisms and accurate representation of the original microbial load. *Sample brought in sterile plastic container* - Using a **sterile container** is essential for preventing **contamination** from external sources. - A non-sterile container would introduce environmental microbes, leading to misleading culture results. *Sample obtained after cleaning the collection site* - **Cleaning the collection site** reduces the presence of **normal flora** or skin contaminants. - This practice helps to ensure that any organisms grown in culture are more likely to be pathogens from the infection site rather than surface contaminants.
Question 9: The most specific test to detect blood stains is:
- A. Benzidine test
- B. Teichmann's test
- C. Spectroscopic test (Correct Answer)
- D. Orthotoluidine test
Explanation: ***Spectroscopic test*** - The **spectroscopic test** is considered the most specific for detecting blood stains because it identifies the characteristic absorption bands of **hemoglobin** and its derivatives. - This test is highly definitive due to the unique **light absorption properties** of blood components, making it less prone to false positives compared to chemical tests. *Benzidine test* - The **benzidine test** is a sensitive preliminary test for blood but is **not specific**, as it reacts with other oxidizing agents (e.g., rust, certain plant peroxidases). - It works by detecting the **peroxidase-like activity of hemoglobin**, leading to color changes but lacks confirmation of blood origin. *Teichmann's test* - **Teichmann's test** (hemin crystal test) is a moderately specific confirmatory test that produces **rhombic crystals of hemin** when heated with glacial acetic acid and a halide salt. - While more specific than presumptive tests, it can sometimes produce **false-negative results** with old or degraded bloodstains and may be less sensitive than spectroscopy. *Orthotoluidine test* - Similar to the benzidine test, the **orthotoluidine test** is another **presumptive test** that detects the peroxidase-like activity of hemoglobin, resulting in a blue-green color change. - It is **highly sensitive but not specific**, meaning it can also give positive reactions with other substances that have similar peroxidase activity, leading to potential false positives.
Question 10: What is the most reliable method to determine the time of death within the first 24 hours after death?
- A. Livor mortis is fixed and cannot be displaced after 8-12 hours
- B. Rigor mortis appears first in smaller muscles and progresses to larger muscles
- C. Putrefaction begins immediately after death in all environmental conditions
- D. Algor mortis using rectal temperature with standard nomograms (Correct Answer)
Explanation: ***Algor mortis using rectal temperature with standard nomograms*** - **Algor mortis** (body cooling) measured via **rectal temperature** using standardized nomograms (such as **Henssge's nomogram**) is considered the **most reliable method** for estimating time of death within the first 24 hours. - While environmental factors affect cooling rate, the use of **mathematical models and nomograms** that account for body weight, ambient temperature, and clothing make this method more **objective and reproducible** than other postmortem changes. - Provides **quantitative data** that can be standardized, unlike the more subjective assessments of rigor or livor mortis. *Rigor mortis appears first in smaller muscles and progresses to larger muscles* - **Rigor mortis** follows **Nysten's rule** (progression from smaller to larger muscles), typically appearing within 2-6 hours, peaking at 12-24 hours. - However, the **onset time is highly variable** depending on factors like ante-mortem physical activity, environmental temperature, and cause of death. - The subjective nature of assessment and **significant individual variation** make it less reliable than temperature-based methods for precise time estimation. *Livor mortis is fixed and cannot be displaced after 8-12 hours* - **Livor mortis** (postmortem lividity) becomes fixed and non-blanchable after approximately 8-12 hours. - While useful, the **wide time range** for fixation and the fact that it provides only a few discrete time points (appearance, confluence, fixation) make it less precise than continuous temperature measurements. *Putrefaction begins immediately after death in all environmental conditions* - This statement is **incorrect**. **Putrefaction** (bacterial decomposition) typically begins hours to days after death, heavily dependent on **environmental temperature** and humidity. - Putrefaction is useful for estimating time of death **beyond 24-48 hours**, not within the first 24 hours as asked in this question.
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