CLINICAL LABORATORY SCIENTIST (CLS)
EXAMINATION
100 PRACTICE QUESTIONS WITH ANSWERS AND
RATIONALES
2026–2027 TESTING CYCLE
SECTION 1: HEMATOLOGY (Questions 1–20)
Question 1: Which anticoagulant is most commonly used for complete blood count (CBC)
testing?
Answer: EDTA
Rationale: EDTA chelates calcium and preserves cellular morphology, making it the standard
anticoagulant for CBCs. Sodium citrate is used for coagulation studies, heparin for chemistry
testing, and oxalate for some special studies.
Question 2: A patient has a hematocrit of 30%, hemoglobin of 10 g/dL, and MCV of 70 fL.
Which type of anemia is suggested?
Answer: Microcytic anemia
,Rationale: Microcytic anemia is indicated by a low MCV (<80 fL). The low hemoglobin and
hematocrit support the presence of anemia. Normocytic anemia has normal MCV, and
macrocytic anemia has high MCV.
Question 3: Which leukocyte is primarily involved in allergic reactions and parasitic infections?
Answer: Eosinophil
Rationale: Eosinophils play a key role in mediating hypersensitivity reactions and combating
multicellular parasites. Neutrophils are primarily involved in bacterial infections, lymphocytes
in viral immunity, and monocytes in phagocytosis.
Question 4: A patient's hemoglobin is critically low. Which test should be performed to confirm
the type of anemia?
Answer: Reticulocyte count
Rationale: The reticulocyte count assesses bone marrow response to anemia. It helps
differentiate between hypoproliferative anemias (low reticulocyte count) and hemolytic anemias
(high reticulocyte count).
Question 5: Which of the following cells is the primary precursor of platelets?
Answer: Megakaryocyte
,Rationale: Megakaryocytes are the bone marrow cells that produce platelets through
fragmentation of their cytoplasm. Myeloblasts give rise to granulocytes, erythroblasts to red
blood cells, and lymphoblasts to lymphocytes.
Question 6: A peripheral blood smear shows numerous target cells, basophilic stippling, and
occasional ringed sideroblasts. What condition is most likely?
Answer: Thalassemia
Rationale: Target cells, basophilic stippling, and ringed sideroblasts are characteristic findings
in thalassemia. Lead poisoning may show basophilic stippling but not target cells or ringed
sideroblasts.
Question 7: The presence of Howell-Jolly bodies in a peripheral blood smear indicates:
Answer: Splenic dysfunction
Rationale: Howell-Jolly bodies are nuclear remnants normally removed by the spleen. Their
presence indicates splenic dysfunction or absence (post-splenectomy).
Question 8: Which of the following is a characteristic finding in chronic myelogenous leukemia
(CML)?
Answer: Philadelphia chromosome
, Rationale: The Philadelphia chromosome (t(9;22)) is found in over 95% of CML cases. Auer
rods are seen in acute myeloid leukemia, schistocytes in microangiopathic hemolytic anemia,
and target cells in thalassemia or liver disease.
Question 9: A patient has a prolonged PT but normal PTT. This suggests a deficiency of which
factor?
Answer: Factor VII
Rationale: The PT test evaluates the extrinsic pathway and common pathway. Factor VII is
specific to the extrinsic pathway, so a deficiency causes prolonged PT with normal PTT. Factor
VIII, IX, and XI deficiencies cause prolonged PTT.
Question 10: Which condition is associated with an elevated mean corpuscular volume (MCV)?
Answer: Vitamin B12 deficiency
Rationale: Vitamin B12 deficiency causes macrocytic anemia with elevated MCV. Iron
deficiency and thalassemia cause microcytic anemia. Aplastic anemia typically presents with
normocytic indices.
Question 11: What is the primary function of the red blood cell?
Answer: Oxygen transport
EXAMINATION
100 PRACTICE QUESTIONS WITH ANSWERS AND
RATIONALES
2026–2027 TESTING CYCLE
SECTION 1: HEMATOLOGY (Questions 1–20)
Question 1: Which anticoagulant is most commonly used for complete blood count (CBC)
testing?
Answer: EDTA
Rationale: EDTA chelates calcium and preserves cellular morphology, making it the standard
anticoagulant for CBCs. Sodium citrate is used for coagulation studies, heparin for chemistry
testing, and oxalate for some special studies.
Question 2: A patient has a hematocrit of 30%, hemoglobin of 10 g/dL, and MCV of 70 fL.
Which type of anemia is suggested?
Answer: Microcytic anemia
,Rationale: Microcytic anemia is indicated by a low MCV (<80 fL). The low hemoglobin and
hematocrit support the presence of anemia. Normocytic anemia has normal MCV, and
macrocytic anemia has high MCV.
Question 3: Which leukocyte is primarily involved in allergic reactions and parasitic infections?
Answer: Eosinophil
Rationale: Eosinophils play a key role in mediating hypersensitivity reactions and combating
multicellular parasites. Neutrophils are primarily involved in bacterial infections, lymphocytes
in viral immunity, and monocytes in phagocytosis.
Question 4: A patient's hemoglobin is critically low. Which test should be performed to confirm
the type of anemia?
Answer: Reticulocyte count
Rationale: The reticulocyte count assesses bone marrow response to anemia. It helps
differentiate between hypoproliferative anemias (low reticulocyte count) and hemolytic anemias
(high reticulocyte count).
Question 5: Which of the following cells is the primary precursor of platelets?
Answer: Megakaryocyte
,Rationale: Megakaryocytes are the bone marrow cells that produce platelets through
fragmentation of their cytoplasm. Myeloblasts give rise to granulocytes, erythroblasts to red
blood cells, and lymphoblasts to lymphocytes.
Question 6: A peripheral blood smear shows numerous target cells, basophilic stippling, and
occasional ringed sideroblasts. What condition is most likely?
Answer: Thalassemia
Rationale: Target cells, basophilic stippling, and ringed sideroblasts are characteristic findings
in thalassemia. Lead poisoning may show basophilic stippling but not target cells or ringed
sideroblasts.
Question 7: The presence of Howell-Jolly bodies in a peripheral blood smear indicates:
Answer: Splenic dysfunction
Rationale: Howell-Jolly bodies are nuclear remnants normally removed by the spleen. Their
presence indicates splenic dysfunction or absence (post-splenectomy).
Question 8: Which of the following is a characteristic finding in chronic myelogenous leukemia
(CML)?
Answer: Philadelphia chromosome
, Rationale: The Philadelphia chromosome (t(9;22)) is found in over 95% of CML cases. Auer
rods are seen in acute myeloid leukemia, schistocytes in microangiopathic hemolytic anemia,
and target cells in thalassemia or liver disease.
Question 9: A patient has a prolonged PT but normal PTT. This suggests a deficiency of which
factor?
Answer: Factor VII
Rationale: The PT test evaluates the extrinsic pathway and common pathway. Factor VII is
specific to the extrinsic pathway, so a deficiency causes prolonged PT with normal PTT. Factor
VIII, IX, and XI deficiencies cause prolonged PTT.
Question 10: Which condition is associated with an elevated mean corpuscular volume (MCV)?
Answer: Vitamin B12 deficiency
Rationale: Vitamin B12 deficiency causes macrocytic anemia with elevated MCV. Iron
deficiency and thalassemia cause microcytic anemia. Aplastic anemia typically presents with
normocytic indices.
Question 11: What is the primary function of the red blood cell?
Answer: Oxygen transport
