MCQ: Pathology

15 clinical MCQs in Pathology. A 45-year-old male develops sudden fever, flank pain, and red-brown urine shortly after a

Questions, Answers & Explanations

1. Q1. A 45-year-old male develops sudden fever, flank pain, and red-brown urine shortly after a blood transfusion begins. What is the most crucial initial management step?

   • Immediately stop the transfusion and maintain intravenous access with normal saline.
   • Administer a broad-spectrum antibiotic and closely monitor for signs of septic shock.
   • Obtain blood cultures from the patient and the blood bag, then notify the blood bank.
   • Administer intravenous paracetamol and antihistamines, then slow down the transfusion rate.

   Answer: Immediately stop the transfusion and maintain intravenous access with normal saline.

   Explanation: The symptoms described are classic for an acute haemolytic transfusion reaction, which is the most serious immediate reaction. The most critical first step is to immediately stop the transfusion to prevent further haemolysis and potential life-threatening complications. Maintaining IV access with normal saline is also important for supportive care. Other steps like sending samples and administering specific treatments follow this initial action.

2. Q2. A primigravida, who is Rh-negative, delivers an Rh-positive baby. What is the primary mechanism by which anti-D immunoglobulin prevents Haemolytic Disease of the Newborn in subsequent pregnancies?

   • It directly neutralizes fetal Rh-positive red blood cells that enter the maternal circulation during delivery.
   • It binds to fetal Rh-positive red blood cells in the maternal circulation, preventing maternal sensitization to the D antigen.
   • It actively suppresses the mother's immune system, thereby inhibiting the production of anti-D IgG antibodies.
   • It enhances the breakdown of maternal anti-D antibodies, limiting their passage across the placenta to a future fetus.

   Answer: It binds to fetal Rh-positive red blood cells in the maternal circulation, preventing maternal sensitization to the D antigen.

   Explanation: Anti-D immunoglobulin (Rhogam) works by binding to any fetal Rh-positive red blood cells that enter the Rh-negative mother's circulation. This 'coats' the fetal cells, leading to their rapid clearance by the maternal reticuloendothelial system before the mother's immune system can recognize the D antigen and mount an immune response (sensitization).

3. Q3. A patient develops acute respiratory distress within two hours of a blood transfusion. Clinical assessment reveals a normal jugular venous pressure (JVP) and blood pressure, with a chest X-ray showing bilateral pulmonary infiltrates and a normal heart size. Which of the following conditions is most consistent with these findings?

   • Transfusion-associated circulatory overload (TACO) due to excessive fluid administration.
   • An acute haemolytic transfusion reaction leading to non-cardiogenic pulmonary oedema.
   • Transfusion-related acute lung injury (TRALI) resulting from donor anti-leukocyte antibodies.
   • Severe bacterial contamination of the blood product causing profound septic shock.

   Answer: Transfusion-related acute lung injury (TRALI) resulting from donor anti-leukocyte antibodies.

   Explanation: The clinical picture of acute respiratory distress, normal JVP and blood pressure, and bilateral pulmonary infiltrates with a normal heart size on CXR, all occurring within 6 hours of transfusion, is highly characteristic of TRALI. TRALI is a non-cardiogenic pulmonary oedema caused by donor antibodies (anti-HLA/anti-neutrophil) attacking recipient leukocytes in the lungs. TACO would present with elevated BP and JVP and often cardiomegaly on CXR. Acute haemolytic reaction would have signs of haemolysis, and bacterial contamination would present with severe hypotension and septic shock.

4. Q4. A patient experiences an unexpected drop in haemoglobin and mild jaundice approximately 7 days after receiving a blood transfusion. A direct antiglobulin test (DAT) is positive. Which blood group system is most notoriously associated with this type of reaction?

   • The ABO blood group system due to common pre-formed IgM antibodies.
   • The Rh blood group system, often involving anti-D following Rh-positive exposure.
   • The Duffy blood group system, known for its association with malaria resistance.
   • The Kidd blood group system, notorious for causing anamnestic antibody responses.

   Answer: The Kidd blood group system, notorious for causing anamnestic antibody responses.

   Explanation: The timing (3-10 days post-transfusion), fall in Hb, mild jaundice, and positive DAT are consistent with a delayed haemolytic transfusion reaction (DHTR). DHTRs occur when low-level alloantibodies, often not detected on initial antibody screens, are boosted by the transfused RBCs, leading to an anamnestic immune response. The Kidd blood group system is particularly notorious for causing these types of reactions, as Kidd antibodies can rapidly disappear from circulation, making them difficult to detect prior to transfusion.

5. Q5. Which of the following blood products has the shortest shelf life and the highest risk of bacterial contamination, primarily due to its specific storage temperature?

   • Platelet concentrates, stored at 20-24°C with constant agitation for 5 days.
   • Packed red blood cells, stored at 1-6°C for up to 35-42 days.
   • Fresh frozen plasma, stored at -18°C for up to 12 months.
   • Cryoprecipitate, stored frozen at -18°C for an extended period of 12 months.

   Answer: Platelet concentrates, stored at 20-24°C with constant agitation for 5 days.

   Explanation: Platelet concentrates are stored at room temperature (20-24°C) with agitation for only 5 days. This warmer storage temperature, necessary to maintain platelet function, unfortunately also provides an ideal environment for bacterial growth, making them the blood product with the highest risk of bacterial contamination and shortest shelf life.

6. Q6. A severely immunocompromised patient requires a blood transfusion. To prevent a rare but highly fatal transfusion reaction, which specific modification should be requested for the blood product?

   • Leukoreduction to remove white blood cells and prevent febrile non-haemolytic reactions.
   • Irradiation with gamma radiation to inactivate donor T-lymphocytes.
   • Washing with saline to remove plasma proteins and prevent allergic reactions.
   • CMV-negative blood from seronegative donors to prevent cytomegalovirus transmission.

   Answer: Irradiation with gamma radiation to inactivate donor T-lymphocytes.

   Explanation: Transfusion-associated Graft-versus-Host Disease (TA-GvHD) is a rare but highly fatal complication, especially in immunocompromised patients. It occurs when viable donor T-lymphocytes engraft in the recipient and attack host tissues. Irradiation of blood products with gamma radiation inactivates these donor T-lymphocytes, effectively preventing TA-GvHD.

7. Q7. A direct antiglobulin test (DAT) is performed on a patient's blood sample. What does a positive result in this test specifically indicate?

   • The presence of free antibodies circulating in the patient's serum that can react with donor red cells.
   • The patient has previously been sensitized to blood group antigens and has developed alloantibodies.
   • Antibodies are already bound to the patient's own red blood cells within their circulatory system.
   • The patient's serum is incompatible with a panel of reagent red blood cells during pre-transfusion screening.

   Answer: Antibodies are already bound to the patient's own red blood cells within their circulatory system.

   Explanation: The Direct Antiglobulin Test (DAT), also known as direct Coombs test, detects antibodies or complement components that are already coating the patient's own red blood cells in vivo. A positive DAT indicates that the patient's RBCs are actively coated with antibodies, which can be seen in conditions like autoimmune haemolytic anaemia, haemolytic transfusion reactions, or HDN. The Indirect Antiglobulin Test (IAT) detects free antibodies in the serum.

8. Q8. A patient undergoing massive transfusion for severe trauma is at risk for various metabolic complications. Which of the following is a direct consequence of citrate in stored blood?

   • Hyperkalaemia, resulting from potassium leaking out of red blood cells during prolonged storage.
   • Metabolic acidosis, due to the low pH of stored blood and impaired tissue perfusion.
   • Dilutional coagulopathy, caused by the replacement of clotting factors and platelets with red cells.
   • Hypocalcaemia, as citrate chelates circulating calcium ions, reducing their effective concentration.

   Answer: Hypocalcaemia, as citrate chelates circulating calcium ions, reducing their effective concentration.

   Explanation: Citrate is used as an anticoagulant in stored blood. During massive transfusion, large amounts of citrate can be infused, overwhelming the liver's ability to metabolize it. Citrate binds to and chelates circulating calcium ions, leading to a reduction in ionized calcium and causing hypocalcaemia. Hyperkalaemia, metabolic acidosis, and dilutional coagulopathy are other complications of massive transfusion but are not directly caused by citrate chelation.

9. Q9. A patient is identified as a 'universal recipient' in the ABO blood group system. Which of the following correctly describes their antigen and antibody profile?

   • Possesses both A and B antigens on their red cells, with no anti-A or anti-B antibodies in their plasma.
   • Lacks both A and B antigens on their red cells, but has both anti-A and anti-B antibodies in their plasma.
   • Possesses A antigens on their red cells and anti-B antibodies in their plasma, but lacks B antigens.
   • Possesses B antigens on their red cells and anti-A antibodies in their plasma, but lacks A antigens.

   Answer: Possesses both A and B antigens on their red cells, with no anti-A or anti-B antibodies in their plasma.

   Explanation: Individuals with AB blood group are considered universal recipients for red blood cells. They possess both A and B antigens on their red blood cells and, critically, lack anti-A and anti-B antibodies in their plasma. This means they will not react to A or B antigens from transfused red cells, allowing them to receive blood from all ABO groups.

10. Q10. A patient experiences a severe anaphylactic reaction immediately following the initiation of a blood transfusion. This type of reaction is most commonly associated with which specific underlying patient condition?

    • Pre-existing antibodies reacting against donor leukocyte HLA antigens, causing cytokine release.
    • IgA deficiency, where the patient has anti-IgA antibodies reacting to trace IgA in donor plasma.
    • Antibodies against donor red cell ABO antigens, leading to rapid intravascular haemolysis.
    • Recipient IgE antibodies reacting to various donor plasma proteins, causing urticaria.

    Answer: IgA deficiency, where the patient has anti-IgA antibodies reacting to trace IgA in donor plasma.

    Explanation: Severe anaphylactic transfusion reactions are most commonly seen in patients with congenital IgA deficiency who have developed anti-IgA antibodies. Even trace amounts of IgA in donor plasma can trigger a severe, life-threatening anaphylactic response in these individuals. Allergic/urticarial reactions are typically less severe and are due to IgE antibodies against donor plasma proteins.

11. Q11. Individuals who are Duffy-null are known to possess a natural resistance to a specific infectious disease. Which of the following infections is associated with resistance in Duffy-null individuals?

    • Plasmodium falciparum malaria, due to a specific genetic mutation affecting RBC invasion.
    • Cytomegalovirus infection, through altered receptor expression on red blood cell surfaces.
    • Plasmodium vivax malaria, as the Duffy antigen serves as a crucial receptor for parasite entry.
    • Parvovirus B19 infection, by preventing viral binding to the P antigen on erythrocytes.

    Answer: Plasmodium vivax malaria, as the Duffy antigen serves as a crucial receptor for parasite entry.

    Explanation: Duffy-null individuals (lacking the Duffy antigen on their red blood cells) are resistant to Plasmodium vivax malaria. This is because the Duffy antigen acts as a receptor for P. vivax parasites to enter red blood cells. Without this receptor, the parasites cannot effectively infect the RBCs, conferring natural resistance.

12. Q12. A patient develops a fever of 38.5°C and chills during a blood transfusion, without any signs of haemolysis or urticaria. Which preventative measure is most effective against this common transfusion reaction?

    • Pre-medicating the patient with antihistamines to block IgE-mediated immune responses.
    • Washing red blood cells with saline to remove residual plasma proteins and reduce antigen exposure.
    • Administering prophylactic corticosteroids to broadly suppress the recipient's immune system.
    • Using leukoreduced blood products, which remove donor white blood cells and their associated cytokines.

    Answer: Using leukoreduced blood products, which remove donor white blood cells and their associated cytokines.

    Explanation: The symptoms of fever and chills without haemolysis or urticaria are characteristic of a febrile non-haemolytic transfusion reaction (FNHTR), the most common transfusion reaction. FNHTRs are caused by recipient antibodies reacting against donor leukocyte HLA antigens or by the accumulation of cytokines in stored blood. Leukoreduction (filtration to remove white blood cells) is the most effective preventative measure as it reduces the number of donor leukocytes and the cytokines they release, thus reducing the likelihood of FNHTR.

13. Q13. The sodium metabisulfite test is used as a screening tool in haematology. What is the primary limitation of this specific test?

    • It confirms the presence of haemoglobin S but cannot differentiate between sickle cell trait and sickle cell disease.
    • It can only detect homozygous sickle cell disease (HbSS) and is insensitive for heterozygous carriers (HbAS).
    • It is prone to false-positive results in patients with other severe anaemias, such as thalassemia.
    • It requires advanced laboratory equipment and is not suitable for rapid bedside diagnostic screening.

    Answer: It confirms the presence of haemoglobin S but cannot differentiate between sickle cell trait and sickle cell disease.

    Explanation: The sodium metabisulfite test (sickling test) works by creating a deoxygenating environment, causing HbS to polymerize and sickling of red blood cells. While it effectively confirms the presence of haemoglobin S, it cannot distinguish between individuals with sickle cell trait (HbAS) and those with sickle cell disease (HbSS), as both will show sickling. Haemoglobin electrophoresis is required to differentiate between these conditions.

14. Q14. In an emergency situation where a patient's blood group is unknown and immediate transfusion of red blood cells is required, which of the following blood products should be administered first?

    • Type-specific A positive packed red blood cells to minimize the risk of a severe allergic reaction.
    • O negative packed red blood cells, as they are considered the universal red cell donor in emergencies.
    • AB positive fresh frozen plasma, due to its low immunogenicity and rapid availability for transfusion.
    • Group B packed red blood cells, which are readily available and widely compatible for most recipients.

    Answer: O negative packed red blood cells, as they are considered the universal red cell donor in emergencies.

    Explanation: In an emergency when the patient's blood group is unknown, O negative packed red blood cells are administered. O negative red cells lack A, B, and Rh D antigens, making them the 'universal red cell donor,' and thus compatible with recipients of all ABO and Rh types. AB positive FFP is the universal plasma donor, not red cells.

15. Q15. A female patient, previously sensitized during pregnancy, develops sudden severe thrombocytopenia with widespread purpura 8 days after a blood transfusion. This clinical picture is most consistent with which transfusion reaction?

    • Transfusion-associated circulatory overload (TACO), indicated by acute respiratory distress and hypertension.
    • Acute haemolytic transfusion reaction, characterized by intravascular haemolysis and renal failure.
    • Post-transfusion purpura, involving antibodies against HPA-1a leading to the destruction of recipient platelets.
    • Delayed haemolytic transfusion reaction, presenting with a gradual drop in haemoglobin and mild jaundice.

    Answer: Post-transfusion purpura, involving antibodies against HPA-1a leading to the destruction of recipient platelets.

    Explanation: The timing (5-10 days post-transfusion), severe thrombocytopenia, purpura, and history of prior sensitization (e.g., pregnancy) are classic features of post-transfusion purpura (PTP). In PTP, the patient develops antibodies (most commonly anti-HPA-1a) against a platelet-specific antigen on donor platelets. These antibodies then cross-react with and destroy the patient's own platelets, leading to severe thrombocytopenia. The other options describe different transfusion reactions with distinct clinical presentations.