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CSMLS MLT Exam practice questions

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Question 1Clinical Chemistry

A serum sample is left on the clot at room temperature for several hours before centrifugation. Which analyte is most likely to show a falsely elevated result because of this delay?

  1. Chloride
  2. Potassium Correct answer.
  3. Glucose
  4. Sodium

Explanation

Prolonged contact of serum with cells allows potassium to leak from erythrocytes and platelets into the serum, raising the measured concentration. Prompt separation of serum from the clot limits this preanalytical error. Sodium, chloride and glucose are not increased by cellular leakage in the same way.

Question 2Clinical Chemistry

Which specimen type is preferred when a fasting lipid profile is requested and the patient has a fragile vein that repeatedly hemolyzes?

  1. Plasma from a lithium heparin tube Correct answer.
  2. Plasma from an EDTA tube
  3. Whole blood from a capillary finger puncture
  4. Serum from a plain tube

Explanation

Lithium heparin plasma is acceptable for lipid measurement and avoids the hemolysis-prone clotting step, while EDTA plasma is unsuitable because the anticoagulant dilutes and chelates the sample. Serum is the usual matrix but requires complete clotting and centrifugation. Capillary whole blood is not used for routine lipid panels.

Question 3Clinical Chemistry

A patient's serum shows a markedly lipemic appearance. Which interference is most likely when measuring sodium by indirect ion-selective electrode?

  1. No interference because ISEs are unaffected by lipids
  2. Falsely high sodium due to light scattering
  3. Falsely low sodium due to protein binding
  4. Falsely low sodium due to electrolyte exclusion Correct answer.

Explanation

Indirect ISEs measure sodium in the diluted sample, and the lipid phase displaces plasma water, so the result is falsely low, a phenomenon called pseudohyponatremia. Direct ISEs are not affected in this way. Light scattering affects photometric methods rather than ion-selective electrodes.

Question 4Clinical Chemistry

Which formula correctly expresses the anion gap?

  1. Na − (Cl + HCO3) Correct answer.
  2. Cl − (Na + HCO3)
  3. (Na + K) − (Cl + HCO3)
  4. (Na + Cl) − (K + HCO3)

Explanation

The anion gap is calculated as sodium minus the sum of chloride and bicarbonate, representing the unmeasured anions. Some laboratories include potassium, but the standard formula without potassium is the classic expression. The other arrangements invert or misplace the measured ions.

Question 5Clinical Chemistry

A patient has a blood pH of 7.28, a PCO2 of 30 mmHg and a bicarbonate of 14 mmol/L. Which acid-base disturbance is present?

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

Explanation

The low pH indicates acidemia, and the low bicarbonate indicates a metabolic cause. The low PCO2 reflects respiratory compensation (hyperventilation). Therefore the primary disorder is metabolic acidosis.

Question 6Clinical Chemistry

Which enzyme is most specific for acute pancreatitis when measured in serum?

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

Explanation

Lipase is more pancreas-specific than amylase and remains elevated longer, making it the preferred marker for acute pancreatitis. Alkaline phosphatase reflects hepatobiliary and bone sources, and CK and LDH are not pancreas-specific.

Question 7Clinical Chemistry

A patient with suspected myocardial infarction has a troponin I result that is elevated but the sample was collected 2 hours after symptom onset. What is the most appropriate interpretation?

  1. The result supports myocardial injury, but serial sampling is still recommended Correct answer.
  2. The result is likely a false positive because troponin rises only after 12 hours
  3. The result confirms infarction and no further sampling is needed
  4. The result should be repeated only if the patient develops chest pain again

Explanation

High-sensitivity troponin assays can detect elevation within 2-3 hours of injury, but serial testing is used to demonstrate the rise and fall required for diagnosis. A single early result supports injury but does not alone establish the kinetics. Repeat sampling is standard practice.

Question 8Clinical Chemistry

Which analyte is used primarily to assess glomerular filtration rate in a 24-hour urine collection?

  1. Urine protein
  2. Urine osmolality
  3. Urine glucose
  4. Creatinine clearance Correct answer.

Explanation

Creatinine clearance compares creatinine excreted in a timed urine collection with the serum concentration to estimate GFR. Glucose and protein in urine reflect other aspects of renal function, and osmolality assesses concentrating ability rather than filtration.

Question 9Clinical Chemistry

A patient has a serum urea of 25 mmol/L and a creatinine of 100 µmol/L, both expressed in SI units. Which condition best explains this pattern?

  1. Liver failure
  2. Acute tubular necrosis
  3. Advanced chronic kidney disease
  4. Dehydration with prerenal azotemia Correct answer.

Explanation

A markedly elevated urea with a normal creatinine suggests prerenal azotemia, where reduced renal perfusion increases urea reabsorption while creatinine remains relatively unchanged. Advanced kidney disease would raise both. Liver failure tends to lower urea because of impaired synthesis.

Question 10Clinical Chemistry

Which laboratory finding is most characteristic of primary hypothyroidism?

  1. Elevated TSH with elevated free T4
  2. Suppressed TSH with elevated free T4
  3. Normal TSH with low free T4
  4. Elevated TSH with low free T4 Correct answer.

Explanation

In primary hypothyroidism the thyroid gland fails to produce hormone, so free T4 falls and the pituitary responds with increased TSH. Suppressed TSH with high free T4 indicates hyperthyroidism. The other patterns are less typical of primary thyroid failure.

Question 11Clinical Chemistry

A patient with a known thyroid disorder has a total T4 that appears normal but a free T4 that is elevated. Which condition could produce this discrepancy?

  1. Low albumin with normal thyroid function
  2. Increased thyroid-binding globulin Correct answer.
  3. Nephrotic syndrome
  4. Androgen therapy

Explanation

Increased thyroid-binding globulin raises total T4 while free T4 may remain normal or, in some states, be affected differently. Total hormone measurements depend on binding proteins, so free hormone is the more reliable index. Nephrotic syndrome and androgen therapy lower binding proteins.

Question 12Clinical Chemistry

Which assay principle underlies the measurement of glycated hemoglobin by ion-exchange HPLC?

  1. Separation of hemoglobin species by charge Correct answer.
  2. Separation by molecular size
  3. Antigen-antibody binding
  4. Enzymatic oxidation

Explanation

Ion-exchange HPLC separates hemoglobin variants, including HbA1c, based on differences in charge between the glycated and nonglycated forms. Size separation would describe gel filtration, and the other principles are used in different assay formats.

Question 13Clinical Chemistry

A patient's fasting plasma glucose is 6.8 mmol/L on two occasions. Which interpretation is most appropriate?

  1. Impaired fasting glucose Correct answer.
  2. Normal glucose tolerance
  3. Diagnostic of diabetes mellitus
  4. Hypoglycemia

Explanation

A fasting plasma glucose between 6.1 and 6.9 mmol/L is classified as impaired fasting glucose, a prediabetic state. Diabetes is diagnosed at 7.0 mmol/L or above on repeat testing. Normal fasting glucose is below 6.1 mmol/L.

Question 14Clinical Chemistry

Which statement about the reference interval for a chemistry analyte is correct?

  1. It is the same for every laboratory using the same analyzer
  2. It is derived from the analytical imprecision of the method
  3. It is calculated from a reference population and usually covers the central 95% Correct answer.
  4. It is the range within which all healthy individuals must fall

Explanation

Reference intervals are established from a defined healthy reference population and conventionally span the central 95% of values. By definition, about 5% of healthy people fall outside the interval. Intervals vary with population and method, so they are not identical across laboratories.

Question 15Clinical Chemistry

A control result falls 2.5 standard deviations below the mean on one level only, while the other level is within limits. What is the most appropriate first action?

  1. Report patient results because only one level failed
  2. Recalibrate and immediately repeat the control
  3. Ignore the result because it is within 3 SD
  4. Investigate the cause before reporting patient results Correct answer.

Explanation

A control result outside the acceptable limits triggers investigation of the cause before patient results are released. The 1-2s rule alone is often a warning, but a consistent shift or a result beyond the laboratory's rejection limit requires action. Recalibration without investigation may not address the underlying problem.

Question 16Clinical Chemistry

Which Westgard rule is violated when two consecutive control results exceed the same 2 SD limit on one level?

  1. R-4s
  2. 4-1s
  3. 2-2s Correct answer.
  4. 1-3s

Explanation

The 2-2s rule is violated when two consecutive control values exceed the same 2 SD limit, indicating a systematic error. The 1-3s rule involves a single result beyond 3 SD, and R-4s involves a range between two levels. The 4-1s rule requires four consecutive results beyond 1 SD.

Question 17Clinical Chemistry

A chemistry analyzer shows a within-run coefficient of variation of 1.5% and a between-run CV of 4.0% for a glucose method. Which statement best describes the method's precision?

  1. The method is unacceptable because between-run CV exceeds 3%
  2. Imprecision is greater between runs than within a run Correct answer.
  3. The between-run CV reflects accuracy rather than precision
  4. The within-run CV is the only measure of precision

Explanation

Between-run imprecision incorporates within-run variation plus additional day-to-day factors such as calibration and reagent changes, so it is typically larger. Both CVs describe precision, not accuracy. Acceptability depends on the method's defined performance goals rather than a universal 3% cutoff.

Question 18Clinical Chemistry

Which analyte is measured to assess compliance with a low-fat diet and is also a risk marker for cardiovascular disease?

  1. High-density lipoprotein cholesterol
  2. Apolipoprotein A-I
  3. Total protein
  4. Triglycerides Correct answer.

Explanation

Triglycerides are influenced by dietary fat and carbohydrate intake and are also an independent cardiovascular risk marker. HDL cholesterol is a protective lipoprotein, and apolipoprotein A-I is its major protein. Total protein reflects nutritional and hydration status, not dietary fat compliance.

Question 19Clinical Chemistry

A patient's serum shows a marked increase in LDL cholesterol with normal triglycerides and a family history of premature coronary disease. Which condition is most likely?

  1. Nephrotic syndrome
  2. Cholestasis
  3. Familial hypercholesterolemia Correct answer.
  4. Type III hyperlipoproteinemia

Explanation

Familial hypercholesterolemia is characterized by markedly elevated LDL cholesterol with normal triglycerides and a strong family history of premature atherosclerosis. Type III hyperlipoproteinemia raises both cholesterol and triglycerides. Nephrotic syndrome and cholestasis have different lipid patterns.

Question 20Clinical Chemistry

Which specimen handling practice is required before measuring plasma ammonia?

  1. Collect in a plain tube and allow complete clotting
  2. Store the sample at room temperature for one hour
  3. Place the sample on ice and separate plasma promptly Correct answer.
  4. Expose the sample to air before centrifugation

Explanation

Ammonia is unstable in blood because cellular and enzymatic activity continues after collection, so samples are placed on ice and plasma is separated promptly. Delayed separation or room-temperature storage falsely elevates ammonia. Clotting in a plain tube would also allow continued ammonia production.

Question 21Clinical Chemistry

Which method is the reference procedure for measuring serum calcium?

  1. Atomic absorption spectrophotometry Correct answer.
  2. Ion-selective electrode
  3. Colorimetric o-cresolphthalein complexone
  4. Enzymatic assay

Explanation

Atomic absorption spectrophotometry is the reference method for total calcium because it directly measures the element with high specificity. Colorimetric and ion-selective methods are routine alternatives. Enzymatic assays are not used for calcium.

Question 22Clinical Chemistry

A patient with chronic kidney disease has a low serum calcium and an elevated phosphate. Which mechanism best explains the low calcium?

  1. Increased intestinal absorption of calcium
  2. Reduced renal phosphate excretion with calcium-phosphate precipitation Correct answer.
  3. Increased vitamin D activation
  4. Decreased parathyroid hormone secretion

Explanation

In chronic kidney disease, phosphate retention leads to calcium-phosphate precipitation and deposition in tissues, lowering serum calcium. Impaired vitamin D activation also contributes. Increased intestinal absorption and increased vitamin D activation would raise, not lower, calcium.

Question 23Clinical Chemistry

Which specimen is preferred for measuring ionized calcium?

  1. EDTA plasma
  2. Citrate plasma
  3. Serum from a plain tube
  4. Heparinized whole blood Correct answer.

Explanation

Ionized calcium is measured in heparinized whole blood to avoid the pH and binding changes that occur during clotting. EDTA and citrate chelate calcium and are unsuitable. Serum is not the preferred matrix because clotting alters the ionized fraction.

Question 24Clinical Chemistry

A serum sample for bilirubin measurement is exposed to bright light for several hours before analysis. What effect is most likely?

  1. Falsely elevated direct bilirubin only
  2. No effect on bilirubin
  3. Falsely decreased total bilirubin Correct answer.
  4. Falsely elevated total bilirubin

Explanation

Bilirubin is photosensitive and degrades when exposed to light, so prolonged exposure falsely lowers the measured concentration. Samples should be protected from light. The effect is not limited to the direct fraction, and it does not raise the result.

Question 25Clinical Chemistry

A patient has a serum osmolality of 300 mOsm/kg and a calculated osmolality of 270 mOsm/kg. Which condition could explain this osmolal gap?

  1. Severe hypernatremia
  2. Methanol ingestion Correct answer.
  3. Uremia
  4. Hyperglycemia

Explanation

An osmolal gap greater than about 10 mOsm/kg suggests the presence of unmeasured osmoles such as methanol or ethylene glycol. Hypernatremia, hyperglycemia and uremia raise measured osmolality but are accounted for in the calculated value, so they do not produce a gap.

Question 26Clinical Chemistry

A serum sample is analysed for total protein by the biuret method. Which chemical reaction accounts for the colour produced?

  1. Copper(II) ions in alkaline solution form a violet complex with peptide bonds Correct answer.
  2. Phosphomolybdic acid is reduced by phenolic groups in the protein
  3. Ninhydrin condenses with free amino groups to give a blue chromophore
  4. Dye binds to albumin at pH 4.2 and the absorbance falls as protein rises

Explanation

In the biuret reaction, cupric ions complex with peptide nitrogen atoms in an alkaline medium, producing a violet colour whose absorbance is proportional to the number of peptide bonds and therefore to protein concentration. The reaction requires at least two peptide bonds, so it responds to all proteins rather than albumin alone.

Question 27Clinical Chemistry

A patient with severe vomiting and dehydration has a serum sodium of 158 mmol/L. Which set of changes in serum osmolality and urine specific gravity is most consistent with this presentation?

  1. Increased osmolality and decreased urine specific gravity
  2. Increased osmolality and increased urine specific gravity Correct answer.
  3. Decreased osmolality and decreased urine specific gravity
  4. Decreased osmolality and increased urine specific gravity

Explanation

Hypernatraemia from water loss raises serum osmolality, which stimulates antidiuretic hormone release and concentrates the urine, so specific gravity rises. The combination of high osmolality with concentrated urine fits pure water depletion rather than a dilutional or renal concentrating defect.

Question 28Clinical Chemistry

A serum sample from a patient receiving high-dose intravenous vitamin C gives a falsely low glucose result on a glucose oxidase-based assay, while a hexokinase method on the same sample agrees with the clinical picture. Which explanation best accounts for this discrepancy?

  1. Ascorbate competes with the chromogen and consumes hydrogen peroxide before it can be measured Correct answer.
  2. Ascorbate binds glucose directly and lowers the true glucose concentration
  3. Ascorbate inhibits hexokinase, so the hexokinase method is the unreliable one
  4. Ascorbate raises the pH of the reaction and denatures glucose oxidase

Explanation

Glucose oxidase methods generate hydrogen peroxide, which is then measured in a peroxidase-coupled chromogenic step. Strong reducing agents such as ascorbate scavenge that peroxide, suppressing colour development and producing a falsely low result. Hexokinase methods do not depend on peroxide detection, so they are unaffected.

Question 29Clinical Chemistry

A patient with nephrotic syndrome has a serum albumin of 18 g/L. Which change in the serum protein electrophoresis pattern is most expected?

  1. A low albumin band with an increased alpha-2 globulin fraction Correct answer.
  2. A normal albumin band with a polyclonal increase in the gamma region
  3. A low albumin band with a restricted monoclonal band in the gamma region
  4. A low albumin band with absent alpha-1 and beta fractions

Explanation

Nephrotic syndrome causes urinary loss of albumin, lowering the albumin band, while hepatic synthesis of large carrier proteins such as alpha-2-macroglobulin increases, enlarging the alpha-2 fraction. This is a classic non-selective protein-losing pattern rather than a clonal proliferation.

Question 30Clinical Chemistry

A patient with a suspected overdose has a measured serum osmolality of 340 mOsm/kg and a calculated osmolality of 285 mOsm/kg. Toxic alcohol ingestion is suspected. Which additional laboratory finding would best support ethylene glycol rather than isopropanol ingestion?

  1. A high anion gap metabolic acidosis with an elevated serum lactate that does not resolve with fluid resuscitation Correct answer.
  2. A high anion gap metabolic acidosis with a raised serum ketone concentration
  3. A normal osmolal gap with an elevated serum ethanol concentration
  4. A normal anion gap with an elevated serum acetone

Explanation

Ethylene glycol is metabolised to glycolate and oxalate, producing a high anion gap metabolic acidosis, and glycolate can cross-react in many lactate assays, giving a spuriously raised lactate that persists. Isopropanol is metabolised to acetone, which produces ketosis without a significant metabolic acidosis. The osmolal gap narrows as the parent alcohol is metabolised, so timing affects its size.

Question 31Hematology

A peripheral blood film shows a normochromic, normocytic anemia with marked rouleaux formation and a very high erythrocyte sedimentation rate. Which plasma protein abnormality most directly explains the rouleaux?

  1. Reduced plasma albumin lowering the zeta potential
  2. Increased fibrinogen and immunoglobulins raising plasma viscosity Correct answer.
  3. Increased plasma oncotic pressure expanding red cell volume
  4. Deficiency of clotting factors reducing plasma density

Explanation

Rouleaux occurs when elevated plasma proteins, especially fibrinogen and paraproteins such as immunoglobulins, neutralize the negative surface charge on red cells and allow them to stack like coins. This same protein excess raises the ESR, which is why marked rouleaux and a high ESR appear together.

Question 32Hematology

In the cyanmethemoglobin method for hemoglobin measurement, which reagent converts all hemoglobin forms (except sulfhemoglobin) to a stable colored compound?

  1. Drabkin reagent containing potassium ferricyanide and potassium cyanide Correct answer.
  2. Acetic acid with methylene blue diluent
  3. Sodium citrate anticoagulant with calcium chloride
  4. Wright stain dissolved in methanol

Explanation

Drabkin reagent oxidizes hemoglobin to methemoglobin with ferricyanide and then converts it to cyanmethemoglobin with cyanide, giving a stable absorbance read at 540 nm. The other reagents serve anticoagulation, staining, or manual cell dilution rather than hemoglobin conversion.

Question 33Hematology

A manual chamber count is performed on a 1:20 dilution of blood, and 80 platelets are counted in the appropriate area. Which factor must be applied to convert the chamber count to a final platelet concentration?

  1. Only the dilution factor
  2. Only the chamber depth
  3. Only the area counted
  4. The dilution factor and chamber depth/area constant Correct answer.

Explanation

Final concentration requires multiplying the observed count by both the dilution factor and the chamber conversion constant (depth times area). Using only one of these yields an incorrectly scaled result.

Question 34Hematology

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

  1. Basophilic stippling with decreased osmotic fragility
  2. Schistocytes with normal osmotic fragility
  3. Spherocytes with increased osmotic fragility and absent central pallor Correct answer.
  4. Target cells with increased osmotic fragility

Explanation

Hereditary spherocytosis produces round cells lacking central pallor because of membrane protein defects, and these cells lyse in hypotonic saline more readily than normal red cells. Target cells, schistocytes, and stippling point to other disorders.

Question 35Hematology

A patient with a prolonged activated partial thromboplastin time corrects fully when normal plasma is added in a mixing study. What does this indicate?

  1. The presence of a specific factor VIII inhibitor
  2. Lupus anticoagulant activity
  3. A factor deficiency rather than a circulating inhibitor Correct answer.
  4. Heparin contamination of the sample

Explanation

Immediate correction in a mixing study shows the prolonged clotting time was caused by missing factor activity, which normal plasma supplies. Failure to correct suggests an inhibitor, including lupus anticoagulant or specific factor antibodies.

Question 36Hematology

Which red cell index is calculated directly from the measured hemoglobin and hematocrit and reflects average red cell hemoglobin concentration?

  1. Red cell distribution width
  2. Mean cell hemoglobin concentration Correct answer.
  3. Mean cell volume
  4. Mean cell hemoglobin

Explanation

MCHC equals hemoglobin divided by hematocrit and expresses the average hemoglobin concentration per unit red cell volume. MCV measures size, RDW measures size variation, and MCH expresses hemoglobin per cell.

Question 37Hematology

Which anticoagulant is preferred for routine coagulation testing because it reversibly binds calcium?

  1. Sodium fluoride
  2. Sodium heparin
  3. Sodium citrate Correct answer.
  4. Potassium EDTA

Explanation

Sodium citrate chelates calcium reversibly, and the ratio is standardized at 9 parts blood to 1 part citrate for coagulation assays. EDTA irreversibly chelates calcium and is used for hematology, while heparin and fluoride serve other purposes.

Question 38Hematology

A blood film shows a dimorphic red cell population with microcytes and oval macrocytes. Which laboratory combination best supports combined iron deficiency and megaloblastic anemia?

  1. Normal ferritin with low RDW and target cells
  2. Low ferritin with elevated MCV variation and hypersegmented neutrophils Correct answer.
  3. Elevated ferritin with basophilic stippling
  4. Elevated ferritin with normal MCV and normal neutrophils

Explanation

Iron deficiency lowers ferritin and produces microcytes, while megaloblastic change raises MCV and produces oval macrocytes and hypersegmented neutrophils, creating a dimorphic picture. The combination of low ferritin and megaloblastic features is the diagnostic clue.

Question 39Hematology

In chronic lymphocytic leukemia, which immunophenotype is most typical of the neoplastic cells?

  1. CD5 negative, CD10 positive, CD20 bright
  2. CD5 positive, CD10 positive, TdT positive
  3. CD5 positive, CD23 positive, CD20 dim Correct answer.
  4. CD5 negative, CD23 negative, CD103 positive

Explanation

CLL cells typically co-express CD5 and CD23 with dim CD20, reflecting a mature B-cell neoplasm. CD10 and TdT indicate immature or follicular/mantle neoplasms, and CD103 marks hairy cell leukemia.

Question 40Hematology

Which laboratory finding most strongly suggests disseminated intravascular coagulation in a bleeding patient?

  1. Shortened APTT with elevated fibrinogen
  2. Prolonged PT with normal fibrinogen and normal D-dimer
  3. Isolated prolonged bleeding time with normal platelet count
  4. Prolonged PT and APTT with low fibrinogen and elevated D-dimer Correct answer.

Explanation

DIC consumes clotting factors and fibrinogen while generating fibrin degradation products, so PT and APTT prolong, fibrinogen falls, and D-dimer rises. Isolated or shortened results do not fit consumptive coagulopathy.

Question 41Hematology

A patient has a normocytic anemia, a low reticulocyte count, and a markedly elevated ferritin with normal transferrin saturation. Which condition best fits this pattern?

  1. Iron deficiency anemia
  2. Acute blood loss anemia
  3. Hemolytic anemia
  4. Anemia of chronic inflammation Correct answer.

Explanation

Inflammation raises ferritin as an acute phase reactant and impairs iron release, producing a normocytic anemia with low reticulocyte response and normal or low transferrin saturation. Iron deficiency gives low ferritin, while hemolysis and blood loss raise reticulocytes.

Question 42Hematology

Which finding on the automated analyzer suggests a cold agglutinin interfering with red cell count and MCV?

  1. Isolated elevation of RDW with normal MCV
  2. Normal red cell count with elevated platelet count
  3. Falsely low red cell count and falsely high MCV with a low MCHC Correct answer.
  4. Falsely high red cell count and low MCV with high MCHC

Explanation

Cold agglutinins clump red cells, so analyzers count fewer larger particles, lowering the red cell count and raising MCV, which dilutes the calculated MCHC. Warming the sample usually resolves the discrepancy.

Question 43Hematology

Which feature best distinguishes immune thrombocytopenia from decreased platelet production on a peripheral film?

  1. Normal platelets with marrow fibrosis
  2. Large platelets with normal or increased megakaryocytes in marrow Correct answer.
  3. Small platelets with decreased megakaryocytes
  4. Giant platelets with absent megakaryocytes

Explanation

In immune thrombocytopenia, destruction drives increased marrow megakaryocytes and release of large young platelets. Decreased production shows reduced megakaryocytes and typically normal-sized or small platelets.

Question 44Hematology

A patient with sickle cell disease has a painful crisis. Which laboratory change is expected on the blood film?

  1. Hypersegmented neutrophils with oval macrocytes
  2. Irreversibly sickled cells and target cells Correct answer.
  3. Marked spherocytosis with absent central pallor
  4. Numerous schistocytes with thrombocytopenia

Explanation

Sickle cell disease produces sickled forms and target cells reflecting hemoglobin S polymerization and membrane change. Spherocytes, schistocytes, and megaloblastic changes belong to other disorders.

Question 45Hematology

Which test is most appropriate to confirm a suspected lupus anticoagulant after a prolonged APTT that does not correct with normal plasma?

  1. Mixing study with factor VIII concentrate
  2. Fibrinogen assay and thrombin time
  3. Bleeding time and platelet aggregometry
  4. Phospholipid-dependent clotting assays with platelet neutralization or hexagonal phase phospholipid Correct answer.

Explanation

Lupus anticoagulant is confirmed with phospholipid-dependent assays that demonstrate inhibition reversed by excess phospholipid, such as platelet neutralization or hexagonal phase testing. Factor concentrate, aggregometry, and thrombin time address different pathways.

Question 46Hematology

A bone marrow aspirate shows sheets of blasts that are myeloperoxidase positive and express CD13 and CD33. Which diagnosis is most likely?

  1. Acute lymphoblastic leukemia
  2. Hairy cell leukemia
  3. Chronic lymphocytic leukemia
  4. Acute myeloid leukemia Correct answer.

Explanation

Myeloperoxidase positivity with CD13 and CD33 expression identifies myeloid lineage blasts, supporting acute myeloid leukemia. Lymphoid blasts lack MPO and express different markers, while CLL and hairy cell leukemia are mature B-cell disorders.

Question 47Hematology

Which finding is most consistent with a delta check flag on an automated hematology analyzer?

  1. A single elevated white cell count in a new patient
  2. A slightly low hemoglobin in a known anemic patient
  3. A sudden unexplained change in MCV between consecutive samples from the same patient Correct answer.
  4. A normal platelet count in a healthy donor

Explanation

Delta checks compare current results with the patient's previous values and flag abrupt changes that may indicate sample mix-up, dilution, or a true clinical change. A single result without prior data cannot trigger a delta check.

Question 48Hematology

Which red cell morphology is most characteristic of lead poisoning?

  1. Basophilic stippling with ring sideroblasts Correct answer.
  2. Target cells with spherocytes
  3. Schistocytes with helmet cells
  4. Acanthocytes with spur cells

Explanation

Lead inhibits heme synthesis and pyrimidine 5-prime nucleotidase, producing basophilic stippling and ring sideroblasts. Target cells, schistocytes, and acanthocytes reflect different membrane or fragmentation processes.

Question 49Hematology

A patient has a prolonged thrombin time that corrects with the addition of protamine sulfate. What is the most likely cause?

  1. Dysfibrinogenemia
  2. Vitamin K deficiency
  3. Heparin contamination Correct answer.
  4. Factor XIII deficiency

Explanation

Protamine neutralizes heparin, so correction of a prolonged thrombin time after protamine indicates heparin contamination. Dysfibrinogenemia and factor deficiencies do not correct with protamine.

Question 50Hematology

Which finding best supports a diagnosis of paroxysmal nocturnal hemoglobinuria?

  1. Increased osmotic fragility with spherocytes
  2. Reduced ADAMTS13 activity with schistocytes
  3. Loss of CD55 and CD59 on red cells with increased complement sensitivity Correct answer.
  4. Elevated fetal hemoglobin with target cells

Explanation

PNH arises from a PIGA mutation causing loss of complement-regulatory proteins CD55 and CD59, so red cells lyse with complement activation. Spherocytes, schistocytes, and fetal hemoglobin patterns belong to other disorders.