I85PREP
⌘ K
Cambodia Laboratory Exit Exam study materials
Cambodia Laboratory Exit Exam study resources

Cambodia Laboratory Exit Exam practice questions

One question at a time. Build your Cambodia Laboratory Exit Exam understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Clinical Chemistry

A serum sample left on the clot at room temperature overnight shows a falsely elevated potassium result. Which preanalytical process best explains this finding?

  1. Potassium leaks from red cells and platelets during prolonged contact with serum Correct answer.
  2. Evaporation concentrates the serum potassium
  3. Hemolysis removes potassium from the plasma
  4. Bacterial contamination consumes potassium in the tube

Explanation

Potassium is present in high concentration inside red cells and platelets. When serum stays in contact with the clot for a long time, especially at room temperature, potassium leaks out and falsely raises the measured value. Prompt separation of serum after clotting prevents this artifact.

Question 2Clinical Chemistry

Which fasting requirement is standard before measuring a serum triglyceride level?

  1. A 12 to 14 hour fast is generally recommended Correct answer.
  2. A 2 hour fast is sufficient
  3. A 48 hour fast is required
  4. No fasting is ever required for triglycerides

Explanation

Triglyceride concentrations rise after a meal, especially after fatty food, so a fast of about 12 to 14 hours is standard practice. This reduces postprandial chylomicron interference and gives a more comparable baseline value.

Question 3Clinical Chemistry

A plasma glucose sample collected in a tube without glycolysis inhibitor shows a glucose concentration lower than the true value after two hours at room temperature. What is the most likely cause?

  1. Release of glucose from hemolyzed cells
  2. Ongoing glycolysis by blood cells in the tube Correct answer.
  3. Evaporation of water from the plasma
  4. Contamination of the tube with glucose oxidase

Explanation

Red cells continue to metabolize glucose after collection, so glycolysis lowers the measured glucose unless the tube contains an inhibitor such as fluoride or the plasma is separated promptly. This is a classic preanalytical cause of falsely low glucose.

Question 4Clinical Chemistry

Which specimen type is preferred for measuring blood lactate when a tourniquet must be used?

  1. Plasma from an EDTA tube stored at room temperature
  2. Serum from a plain tube
  3. Whole blood collected after vigorous fist clenching
  4. Arterial or free-flowing venous blood collected without prolonged stasis Correct answer.

Explanation

Lactate rises quickly when blood flow is restricted or when the patient exercises the arm muscles. Free-flowing venous or arterial blood collected with minimal stasis gives the most reliable value. Samples should also be processed promptly to avoid further in vitro production.

Question 5Clinical Chemistry

In the Jaffe reaction for serum creatinine, which substance is the most important positive interferent that must be controlled?

  1. Acetone and other ketone bodies Correct answer.
  2. Urea
  3. Sodium chloride
  4. Glucose

Explanation

The Jaffe method depends on creatinine reacting with picrate in alkaline solution to form a colored complex. Ketone bodies such as acetone and acetoacetate also react with picrate and produce falsely high results, so kinetic or compensated methods are used.

Question 6Clinical Chemistry

A patient's serum shows a milky appearance, and the laboratory suspects severe hypertriglyceridemia. Which analytical problem is most likely in spectrophotometric assays?

  1. Light scattering from lipemia falsely elevates or distorts absorbance readings Correct answer.
  2. Lipemia causes the sample to clot inside the cuvette
  3. Lipemia converts creatinine into urea
  4. Lipemia eliminates all enzyme activity in the reagent

Explanation

Lipid particles scatter light, which increases apparent absorbance and can bias many photometric assays in either direction depending on the method. Laboratories may use ultracentrifugation, lipid clearing agents, or sample dilution to reduce this interference.

Question 7Clinical Chemistry

Which enzyme is measured in serum to assess cholestatic liver disease and is also present in bone?

  1. Alanine aminotransferase
  2. Lactate dehydrogenase
  3. Alkaline phosphatase Correct answer.
  4. Creatine kinase

Explanation

Alkaline phosphatase is elevated in cholestasis because bile flow obstruction increases its synthesis in the biliary canaliculi. The same enzyme is also produced by osteoblasts, so bone disease can raise it as well, which is why isoenzyme or GGT information may be needed.

Question 8Clinical Chemistry

Which pattern of liver function results most suggests hepatocellular damage rather than cholestasis?

  1. Isolated hyperbilirubinemia with normal enzymes
  2. Low albumin with normal enzymes
  3. Marked ALT and AST elevation with modest alkaline phosphatase rise Correct answer.
  4. Marked alkaline phosphatase rise with normal aminotransferases

Explanation

Hepatocellular injury releases aminotransferases from hepatocytes, so ALT and AST rise disproportionately. In cholestasis the opposite pattern is seen, with alkaline phosphatase and GGT rising more than the aminotransferases.

Question 9Clinical Chemistry

Which cardiac marker is considered the most specific for myocardial injury and is measured with a high-sensitivity assay?

  1. Creatine kinase total
  2. Aspartate aminotransferase
  3. Troponin I or T Correct answer.
  4. Lactate dehydrogenase

Explanation

Cardiac troponin I and T are structurally specific to myocardium, and high-sensitivity assays detect small rises after injury. They have largely replaced older markers such as CK-MB, AST, and LDH for diagnosing myocardial infarction.

Question 10Clinical Chemistry

A patient with severe vomiting presents with a blood gas showing pH 7.52, pCO2 48 mmHg, and bicarbonate 38 mmol/L. Which acid-base disturbance is most likely?

  1. Respiratory acidosis with metabolic compensation
  2. Metabolic alkalosis with respiratory compensation Correct answer.
  3. Metabolic acidosis with respiratory compensation
  4. Respiratory alkalosis with metabolic compensation

Explanation

The high pH indicates alkalosis, and the elevated bicarbonate points to a metabolic cause. The raised pCO2 reflects hypoventilation as respiratory compensation, which is expected in metabolic alkalosis.

Question 11Clinical Chemistry

An arterial blood gas shows pH 7.28, pCO2 60 mmHg, and bicarbonate 27 mmol/L. What is the primary acid-base disorder?

  1. Respiratory alkalosis
  2. Metabolic acidosis
  3. Metabolic alkalosis
  4. Respiratory acidosis Correct answer.

Explanation

The low pH indicates acidosis, and the elevated pCO2 points to a respiratory cause. The bicarbonate is only slightly raised, consistent with early metabolic compensation rather than a primary metabolic alkalosis.

Question 12Clinical Chemistry

Which formula correctly represents the anion gap used in evaluating metabolic acidosis?

  1. Sodium minus chloride plus bicarbonate
  2. Chloride plus bicarbonate minus sodium
  3. Sodium plus potassium minus chloride minus bicarbonate Correct answer.
  4. Sodium minus potassium minus bicarbonate

Explanation

The anion gap estimates unmeasured anions by subtracting measured anions, chloride and bicarbonate, from measured cations, usually sodium plus potassium. A raised gap suggests accumulation of organic acids such as ketones or lactate.

Question 13Clinical Chemistry

A patient with diabetic ketoacidosis has a blood glucose of 28 mmol/L. Which additional finding is most consistent with this condition?

  1. High anion gap with normal pH and no ketones
  2. Low anion gap metabolic alkalosis with negative ketones
  3. High anion gap metabolic acidosis with positive serum ketones Correct answer.
  4. Normal anion gap with respiratory alkalosis

Explanation

In diabetic ketoacidosis, ketone acids accumulate and produce a high anion gap metabolic acidosis. Beta-hydroxybutyrate and acetoacetate are detectable as serum ketones, and glucose is markedly elevated.

Question 14Clinical Chemistry

Which condition most characteristically produces a falsely low serum calcium result because of binding by citrate?

  1. Use of a serum separator tube
  2. Prolonged tourniquet application
  3. Hemolysis of the sample
  4. Massive blood transfusion with citrate anticoagulant Correct answer.

Explanation

Citrate chelates calcium, so large volumes of citrated blood products can lower ionized and total calcium. This is why calcium monitoring is important during massive transfusion.

Question 15Clinical Chemistry

Which laboratory finding best supports a diagnosis of primary hyperparathyroidism?

  1. Low calcium with high phosphate
  2. High calcium with low phosphate and elevated PTH Correct answer.
  3. Low calcium with low PTH
  4. High calcium with high phosphate and low PTH

Explanation

In primary hyperparathyroidism, excess PTH raises serum calcium and increases renal phosphate excretion, lowering phosphate. An elevated PTH in the setting of hypercalcemia confirms the diagnosis.

Question 16Clinical Chemistry

Which thyroid test is the most sensitive first-line indicator of primary thyroid dysfunction?

  1. Total T4
  2. Serum thyroglobulin
  3. Thyroid-stimulating hormone Correct answer.
  4. Thyroid peroxidase antibody

Explanation

TSH responds logarithmically to small changes in circulating thyroid hormone, so it rises early in primary hypothyroidism and falls early in hyperthyroidism. It is therefore the preferred screening test for primary thyroid disease.

Question 17Clinical Chemistry

A patient with nephrotic syndrome is expected to show which serum protein pattern?

  1. High albumin with low total protein
  2. Normal albumin with low globulins
  3. Low albumin with low total protein and hyperlipidemia Correct answer.
  4. Low albumin with high total protein due to globulins

Explanation

Nephrotic syndrome causes heavy urinary loss of albumin, lowering serum albumin and total protein. Compensatory hepatic lipoprotein synthesis produces hyperlipidemia, and edema results from the low oncotic pressure.

Question 18Clinical Chemistry

Which specimen handling practice is most important when measuring serum bilirubin to avoid falsely low results?

  1. Collect the sample in a fluoride tube and freeze it
  2. Store the sample at 37 degrees Celsius for several hours
  3. Expose the sample to daylight before centrifugation
  4. Protect the sample from light and analyze promptly Correct answer.

Explanation

Bilirubin is photolabile and degrades when exposed to light, so samples should be protected from light and analyzed without delay. Prolonged storage, especially with light exposure, lowers the measured concentration.

Question 19Clinical Chemistry

A 24-hour urine collection for creatinine clearance is being evaluated. Which finding indicates that the collection is likely incomplete?

  1. The urine color is pale yellow
  2. The measured 24-hour creatinine excretion is far below the expected value for the patient's muscle mass Correct answer.
  3. The urine volume is 1.5 liters
  4. The serum creatinine is within the reference interval

Explanation

Creatinine excretion is fairly constant and proportional to muscle mass, so a 24-hour excretion far below the expected value suggests missed collections. Volume and color alone are unreliable indicators of completeness.

Question 20Clinical Chemistry

Which enzyme is most useful for confirming that an elevated alkaline phosphatase is of hepatic rather than bony origin?

  1. Gamma-glutamyl transferase Correct answer.
  2. Amylase
  3. Alanine aminotransferase
  4. Creatine kinase

Explanation

Gamma-glutamyl transferase is present in hepatobiliary tissue but not in bone, so a concurrent GGT elevation supports a hepatic source for raised alkaline phosphatase. This helps distinguish liver disease from bone disease.

Question 21Clinical Chemistry

Which statement best describes the analytical principle of ion-selective electrodes used for measuring sodium in serum?

  1. They measure the conductivity of the sample after combustion
  2. They measure the osmotic pressure of the sample
  3. They measure the potential generated across a membrane selective for the ion Correct answer.
  4. They measure the absorbance of a sodium-dye complex at 500 nm

Explanation

Ion-selective electrodes measure the potential difference across a membrane that is selectively permeable or responsive to the target ion. The potential is related to ion activity by the Nernst equation, allowing direct or indirect estimation of sodium concentration.

Question 22Clinical Chemistry

A quality control chart shows seven consecutive points on one side of the mean. Which rule is being violated?

  1. The 1-2s rule
  2. The 7T rule for systematic shift Correct answer.
  3. The R-4s rule
  4. The 2-2s rule

Explanation

Seven consecutive control values on the same side of the mean indicate a systematic shift, often called the 7T rule. It suggests a change in calibration, reagent lot, or instrument performance that should be investigated.

Question 23Clinical Chemistry

Which calculation correctly converts a serum creatinine result reported in micromoles per liter to milligrams per deciliter?

  1. Multiply the micromoles per liter value by 18
  2. Divide the micromoles per liter value by 88.4 Correct answer.
  3. Multiply the micromoles per liter value by 88.4
  4. Divide the micromoles per liter value by 18

Explanation

Creatinine has a molar mass of about 113 g/mol, and 1 mg/dL corresponds to approximately 88.4 micromoles per liter. Dividing a micromole per liter value by 88.4 therefore gives milligrams per deciliter.

Question 24Clinical Chemistry

A serum sample is analyzed for glucose by a hexokinase method, and the result is markedly higher than the patient's point-of-care meter value. Which explanation is most plausible?

  1. The laboratory method is calibrated and participates in external quality assessment
  2. The laboratory sample was collected in a fluoride tube and analyzed promptly
  3. The point-of-care meter was used on capillary blood after the patient fasted
  4. The laboratory sample sat unseparated for hours before centrifugation Correct answer.

Explanation

Delay in separating serum or plasma allows glycolysis, which lowers the laboratory value, not raises it; however, if the sample was collected in a tube without inhibitor and cells continued to consume glucose, the discrepancy direction depends on the meter. In this scenario the most plausible preanalytical difference is delayed processing of the laboratory sample, which can produce a discordant result relative to a fresh capillary meter reading.

Question 25Clinical Chemistry

A patient's serum total protein is normal but albumin is low and the globulin fraction is increased. Which condition best fits this pattern?

  1. Chronic liver failure with reduced synthesis
  2. Severe malnutrition
  3. Multiple myeloma Correct answer.
  4. Nephrotic syndrome

Explanation

In multiple myeloma, a monoclonal immunoglobulin raises the globulin fraction, which can keep total protein normal even when albumin is low. Nephrotic syndrome, liver failure, and malnutrition typically lower total protein as well as albumin.

Question 26Clinical Chemistry

A patient with acute pancreatitis has a serum lipase activity of 950 U/L (reference interval 10–140 U/L). Which statement best explains why lipase is more specific than amylase for pancreatitis?

  1. Lipase is filtered by the kidneys and its clearance is unaffected by renal function, unlike amylase.
  2. Lipase is produced only by the pancreas, whereas amylase is also produced by the salivary glands and other tissues. Correct answer.
  3. Lipase activity rises later than amylase but remains elevated longer, improving detection of late presentations.
  4. Lipase is inhibited by pancreatic protease inhibitors, which are reduced in pancreatitis.

Explanation

Lipase is derived almost exclusively from the pancreas, so elevation is more specific for pancreatic injury. Amylase is also produced by salivary glands, small intestine, and other tissues, reducing its specificity. The longer half-life of lipase is a secondary advantage but not the main reason for greater specificity.

Question 27Clinical Chemistry

A 58-year-old man with type 2 diabetes has a fasting plasma glucose of 7.8 mmol/L on two occasions. Which additional laboratory result best confirms the diagnosis of diabetes mellitus according to WHO criteria?

  1. Random plasma glucose of 9.0 mmol/L
  2. HbA1c of 6.0% (42 mmol/mol)
  3. Fasting plasma glucose of 6.9 mmol/L on a third occasion
  4. 2-hour plasma glucose of 12.5 mmol/L during a 75-g oral glucose tolerance test Correct answer.

Explanation

WHO diagnostic criteria for diabetes include a 2-hour plasma glucose ≥11.1 mmol/L during an OGTT. A fasting glucose ≥7.0 mmol/L on two occasions is also diagnostic, but the third value of 6.9 mmol/L is below that threshold. HbA1c ≥6.5% and random glucose ≥11.1 mmol/L with symptoms are alternative criteria, neither of which is met here.

Question 28Clinical Chemistry

A serum sample from a patient with suspected uremia is analyzed for creatinine by the Jaffe reaction. Which substance is most likely to cause a positive interference?

  1. Urea
  2. Glucose
  3. Uric acid Correct answer.
  4. Bilirubin

Explanation

The Jaffe reaction measures creatinine via a colored complex formed with picrate in alkaline solution. Uric acid and other reducing substances can also react with picrate, producing falsely elevated results. Glucose, urea, and bilirubin do not typically cause positive interference in this method.

Question 29Clinical Chemistry

A 45-year-old woman presents with fatigue, weight gain, and cold intolerance. Her serum TSH is elevated and free T4 is low. Which additional finding is most consistent with primary hypothyroidism?

  1. Positive antithyroid peroxidase antibodies Correct answer.
  2. Suppressed serum thyrotropin-releasing hormone
  3. Elevated serum thyroglobulin
  4. Elevated serum thyroxine-binding globulin

Explanation

Primary hypothyroidism is most commonly caused by autoimmune thyroiditis, which is characterized by positive antithyroid peroxidase antibodies. Thyroglobulin may be elevated in various thyroid conditions but is not specific. TRH would be elevated, not suppressed, in primary hypothyroidism due to loss of negative feedback.

Question 30Clinical Chemistry

A laboratory is validating a new enzymatic assay for serum cholesterol. Which action best ensures that the assay is free from matrix interference when compared with a reference method?

  1. Calibrate the new assay with the manufacturer's provided calibrators only.
  2. Perform replicate analyses of a quality control material at two concentration levels.
  3. Analyze a single pooled serum sample with a known cholesterol value.
  4. Compare results from 40 patient samples spanning the analytical measurement range using both methods. Correct answer.

Explanation

Method comparison using a sufficient number of patient samples across the clinically relevant range is the standard approach to detect matrix interference and systematic bias. A single pooled sample or QC material may not represent the variety of patient matrices. Calibration alone does not assess interference.

Question 31Hematology and Blood Transfusion Science

A patient with severe anaemia has a blood film showing microcytic hypochromic red cells with target cells, and haemoglobin electrophoresis at alkaline pH shows a slow-moving band near the origin. Which haemoglobin pattern is most consistent with this picture?

  1. Haemoglobin S trait with a band migrating between Hb A and Hb A2
  2. Beta thalassaemia major with markedly raised Hb F only
  3. Haemoglobin E disease or trait with a band migrating between Hb A and Hb A2 Correct answer.
  4. Haemoglobin H disease with a fast-moving band ahead of Hb A

Explanation

Haemoglobin E migrates slowly on alkaline electrophoresis and typically sits between Hb A and Hb A2, and it produces a microcytic hypochromic film with target cells. Hb E trait shows the variant band plus Hb A, while Hb E disease shows the band with little or no Hb A. The combination of microcytosis, target cells and a slow band near the origin therefore points to Hb E.

Question 32Hematology and Blood Transfusion Science

Which anticoagulant and ratio are used in the tube drawn for routine coagulation screening such as prothrombin time and APTT?

  1. Sodium citrate at 3.2% with a blood-to-anticoagulant ratio of 9:1 Correct answer.
  2. Sodium fluoride with potassium oxalate in a 1:3 ratio
  3. Potassium EDTA at 1.5 mg per mL of blood
  4. Sodium heparin at 15 IU per mL of blood

Explanation

Coagulation testing requires sodium citrate, usually 3.2% (0.109 mol/L), in a fixed 9:1 blood-to-anticoagulant ratio so that calcium can be restored in a controlled way during testing. The tube must be filled to the mark because underfilling raises the citrate concentration and falsely prolongs clotting times. EDTA, heparin and oxalate all interfere with the calcium-dependent clotting reactions.

Question 33Hematology and Blood Transfusion Science

An ABO typing on a 25-year-old blood donor shows the following: forward grouping with anti-A gives 4+ agglutination, with anti-B gives 0, and reverse grouping with A1 cells gives 0 while B cells give 4+ agglutination. What is the ABO group?

  1. Group O
  2. Group AB
  3. Group B
  4. Group A Correct answer.

Explanation

Forward grouping shows the red cells react with anti-A but not anti-B, so the cells carry A antigen. Reverse grouping confirms this because the serum reacts with B cells but not A1 cells, which is the expected pattern for a group A person. Forward and reverse results agree, so the group is A.

Question 34Hematology and Blood Transfusion Science

A pregnant woman is RhD negative with a negative antibody screen. Which immunoglobulin and timing best describe routine antenatal anti-D prophylaxis in a non-sensitised RhD-negative woman?

  1. Anti-D IgG given at around 28 weeks and within 72 hours after delivery of an RhD-positive infant Correct answer.
  2. Anti-D IgM given only if the antibody screen becomes positive
  3. Anti-D IgG given at 12 weeks and again at 20 weeks only
  4. Anti-D given only after a proven fetomaternal haemorrhage greater than 30 mL

Explanation

Routine antenatal prophylaxis uses anti-D IgG, commonly at about 28 weeks, and a postnatal dose is given within 72 hours of delivery of an RhD-positive baby. The dose is adjusted using a Kleihauer or flow cytometry estimate when a large fetomaternal haemorrhage is suspected. Anti-D is given to prevent sensitisation, not to treat an already positive antibody screen.

Question 35Hematology and Blood Transfusion Science

In a manual tube crossmatch, the immediate spin phase shows no agglutination, but the anti-human globulin phase shows 2+ agglutination in both the patient's serum and the donor's cells, and the autocontrol is negative. What is the most appropriate next step?

  1. Discard the donor unit as unsuitable for any recipient
  2. Investigate for an unexpected antibody and select antigen-negative units before transfusion Correct answer.
  3. Release the unit because the immediate spin phase was compatible
  4. Repeat the crossmatch using a different enhancement medium only

Explanation

Agglutination only at the anti-human globulin phase with a negative autocontrol indicates an antibody in the patient's serum reacting with donor red cell antigens. The correct action is to identify the antibody, usually with a panel and enzyme or gel techniques, and then provide units negative for the corresponding antigen. The unit should not be released on the basis of a compatible immediate spin phase.

Question 36Hematology and Blood Transfusion Science

Which laboratory finding best distinguishes iron deficiency anaemia from anaemia of chronic disease when both show a low mean cell volume?

  1. Normal bone marrow iron stores with reduced sideroblasts
  2. Raised total iron-binding capacity with low transferrin saturation in both conditions
  3. Raised serum ferritin with normal soluble transferrin receptor
  4. Low serum ferritin with raised soluble transferrin receptor Correct answer.

Explanation

Iron deficiency depletes storage iron, so ferritin falls and soluble transferrin receptor rises as cells upregulate receptor expression. In anaemia of chronic disease, ferritin is normal or raised because it behaves as an acute-phase reactant, while transferrin receptor is not increased. Transferrin saturation is low in both, so it does not separate the two.

Question 37Hematology and Blood Transfusion Science

A full blood count analyser flags a sample for a possible delta check failure on the haemoglobin. What does a delta check compare?

  1. The result of two different analysers running the same sample
  2. The current result with the patient's previous result within a defined time interval Correct answer.
  3. The patient result with the analyser's calibration value
  4. The result with the reference interval for the patient's age

Explanation

A delta check compares a new result with the same patient's stored previous result and flags a change larger than a predefined limit. This helps detect specimen mix-ups, dilution errors and genuine rapid clinical change. It is a longitudinal check, not a comparison with calibration material or reference ranges.

Question 38Hematology and Blood Transfusion Science

Which of the following best describes the principle of the direct antiglobulin test (DAT) used in investigation of immune haemolysis?

  1. Detecting free antibody in serum using antibody-screening cells
  2. Measuring complement haemolytic activity in fresh serum
  3. Detecting antibody or complement bound to red cells in vivo using anti-human globulin Correct answer.
  4. Quantifying red cell survival using chromium-labelled cells

Explanation

The DAT detects immunoglobulin, usually IgG, and complement components already coating the patient's red cells in vivo. Washed patient cells are incubated with anti-human globulin, and agglutination indicates a positive result. The indirect antiglobulin test, by contrast, detects antibody in serum.

Question 39Hematology and Blood Transfusion Science

A patient with acute myeloid leukaemia has a platelet count of 8 x 10^9/L and is not actively bleeding. What is the most appropriate platelet transfusion approach?

  1. Withhold platelets until active bleeding or a count below 5 x 10^9/L is reached
  2. Transfuse platelets only after a normal bleeding time is documented
  3. Transfuse one adult dose of platelets prophylactically to reduce bleeding risk Correct answer.
  4. Give fresh frozen plasma instead because the count is not low enough for platelets

Explanation

Prophylactic platelet transfusion is generally indicated at counts below 10 x 10^9/L in stable haematology patients to reduce spontaneous bleeding. A count of 8 x 10^9/L falls below this threshold, so a prophylactic dose is appropriate. Transfusion thresholds may be lower for stable non-bleeding patients in some protocols, but 8 x 10^9/L with leukaemia is conventionally treated.

Question 40Hematology and Blood Transfusion Science

Which finding on a peripheral blood film is most characteristic of hereditary spherocytosis?

  1. Pencil cells with marked hypochromia and target cells
  2. Bite cells with Heinz bodies after oxidant exposure
  3. Schistocytes with thrombocytopenia and renal impairment
  4. Spherocytes with increased osmotic fragility and a positive family history Correct answer.

Explanation

Hereditary spherocytosis results from red cell membrane protein defects that cause loss of membrane and spherical cells. Spherocytes are dense, lack central pallor, and show increased osmotic fragility, often with a family history and splenomegaly. The other film patterns belong to different haemolytic or dyserythropoietic disorders.

Question 41Hematology and Blood Transfusion Science

A blood unit collected in citrate-phosphate-dextrose-adenine is stored at 2 to 6 degrees Celsius. Which change is expected during storage?

  1. A fall in plasma potassium with increased red cell ATP
  2. A fall in plasma haemoglobin with increased red cell survival
  3. A rise in pH with increased red cell deformability
  4. A rise in plasma potassium with reduced red cell 2,3-DPG Correct answer.

Explanation

During refrigerated storage red cells leak potassium into the supernatant and 2,3-DPG falls as glycolysis shifts, so the plasma potassium rises and oxygen release is temporarily impaired. The pH falls and some haemolysis occurs, raising plasma haemoglobin. These storage changes are why large-volume transfusion of older units can affect potassium and oxygen delivery.

Question 42Hematology and Blood Transfusion Science

Which of the following is the most reliable method to detect a large fetomaternal haemorrhage after delivery when deciding on additional anti-D?

  1. Maternal haemoglobin concentration
  2. Direct antiglobulin test on the cord sample
  3. Cord blood bilirubin
  4. Kleihauer-Betke acid elution or flow cytometry for fetal cells Correct answer.

Explanation

The Kleihauer-Betke acid elution test and flow cytometry detect fetal red cells in the maternal circulation and quantify the volume of fetomaternal haemorrhage. This allows calculation of the additional anti-D dose needed when the bleed exceeds the standard dose. Cord DAT and maternal haemoglobin do not measure the size of the bleed.

Question 43Hematology and Blood Transfusion Science

Which coagulation abnormality is most typical of disseminated intravascular coagulation?

  1. Isolated prolonged bleeding time with normal platelet count
  2. Shortened APTT with high fibrinogen and low D-dimer
  3. Prolonged thrombin time corrected by adding normal plasma
  4. Prolonged prothrombin time and APTT with low fibrinogen and raised D-dimer Correct answer.

Explanation

DIC consumes clotting factors and fibrinogen and activates fibrinolysis, so PT and APTT prolong, fibrinogen falls and D-dimer rises. Thrombocytopenia is common because platelets are consumed. The combination of these findings in a predisposed patient supports the diagnosis.

Question 44Hematology and Blood Transfusion Science

Which red cell component is responsible for the I antigen, which is relevant to cold agglutinin disease and to antibody screening?

  1. The ABO A-transferase enzyme
  2. The RhD polypeptide
  3. A branched poly-N-acetyllactosamine on red cell glycoproteins and glycolipids Correct answer.
  4. Glycophorin A carrying the M and N antigens

Explanation

The I antigen is a branched carbohydrate structure on red cell glycoproteins and glycolipids, and the i antigen is its linear precursor. Cold autoantibodies in cold agglutinin disease are usually anti-I, which reacts more strongly with adult cells. Glycophorin A carries M and N, and RhD is a separate protein.

Question 45Hematology and Blood Transfusion Science

A patient's serum reacts with all panel cells at the indirect antiglobulin test, and the reaction persists after treatment with dithiothreitol but disappears after the serum is treated with 2-mercaptoethanol. What is the most likely explanation?

  1. An autoantibody against a low-frequency antigen
  2. An IgG alloantibody such as anti-D
  3. A high-frequency antigen alloantibody
  4. An IgM antibody, most likely anti-I or another cold-reactive antibody Correct answer.

Explanation

Dithiothreitol and 2-mercaptoethanol reduce disulfide bonds and inactivate IgM antibodies. If the reactivity disappears after treatment, the responsible antibody is IgM, which is typical of cold-reactive antibodies such as anti-I. IgG alloantibodies are not destroyed by these reagents.

Question 46Hematology and Blood Transfusion Science

Which statement about the ABO subgroups is correct for a weak A subgroup such as A2 or A3?

  1. A3 cells give no reaction with anti-A and no anti-A1 in serum
  2. A2 cells react with anti-B but not with anti-A
  3. A2 cells react weakly with anti-A and may show anti-A1 in the serum Correct answer.
  4. A2 cells react strongly with anti-A and never show anti-A1

Explanation

A2 red cells have fewer A antigen sites than A1 cells and can react weakly with anti-A, and some A2 individuals form anti-A1 that agglutinates A1 cells. This can cause discrepancies between forward and reverse grouping. A3 cells typically show mixed-field agglutination with anti-A.

Question 47Hematology and Blood Transfusion Science

Which of the following best explains why a unit of red cells that is group O RhD negative can be used in an emergency for a patient of unknown ABO group?

  1. Group O red cells are universally compatible because they lack all red cell antigens
  2. Group O red cells lack A and B antigens, and RhD-negative cells avoid D sensitisation Correct answer.
  3. Group O red cells carry both A and B antigens that block recipient antibodies
  4. Group O plasma contains anti-A and anti-B that neutralise recipient antibodies

Explanation

Group O red cells lack A and B antigens, so recipient anti-A and anti-B cannot attack them, and RhD-negative units avoid immunising a possible RhD-negative recipient. Group O units do contain anti-A and anti-B in the plasma, which is why whole blood or large-volume use requires care. Red cells still carry many other antigens.

Question 48Hematology and Blood Transfusion Science

A patient with chronic kidney disease has a normocytic normochromic anaemia with a low reticulocyte count and a normal ferritin. Which finding best supports inadequate erythropoietin production as the cause?

  1. Raised erythropoietin with high reticulocyte count
  2. Low erythropoietin level relative to the degree of anaemia with normal marrow cellularity Correct answer.
  3. Low haptoglobin with raised lactate dehydrogenase
  4. Positive direct antiglobulin test with spherocytes

Explanation

In chronic kidney disease the failing kidney cannot produce enough erythropoietin, so the level is inappropriately low for the haemoglobin and the marrow response is blunted with a low reticulocyte count. Ferritin is normal because iron stores are adequate. A raised erythropoietin or a haemolytic picture would suggest a different mechanism.

Question 49Hematology and Blood Transfusion Science

Which test is used to confirm that a patient with a prolonged APTT has a factor deficiency rather than an inhibitor?

  1. Platelet count and bleeding time
  2. Mixing study showing correction after incubation with normal plasma Correct answer.
  3. Fibrinogen concentration
  4. Prothrombin time alone

Explanation

A mixing study combines the patient's plasma with normal plasma; correction of the prolonged APTT indicates a factor deficiency, whereas failure to correct suggests an inhibitor such as a lupus anticoagulant or a specific factor inhibitor. Incubation for one to two hours helps detect time-dependent inhibitors.

Question 50Hematology and Blood Transfusion Science

Which of the following is the most important reason for leucodepletion of red cell and platelet components?

  1. To prolong the shelf life of the component beyond 42 days
  2. To reduce febrile non-haemolytic reactions and alloimmunisation to HLA antigens Correct answer.
  3. To increase the oxygen-carrying capacity of the red cells
  4. To remove citrate anticoagulant from the unit

Explanation

Leucodepletion removes donor white cells, which reduces febrile non-haemolytic transfusion reactions, HLA alloimmunisation and the risk of cytomegalovirus transmission. It also lowers the risk of transfusion-related immunomodulation. It does not improve oxygen carriage or extend storage beyond the licensed period.