ASCP MLS MEDICAL LAB SCIENTIST EXAM | ALL
PRACTICE Q&A 2026/2027 | A+ GRADED |
COMPREHENSIVE EXAM GUIDE 2026&2027
1. A patient’s complete blood count shows a hemoglobin concentration of 7.8 g/dL,
hematocrit of 23%, and MCV of 72 fL. Which additional finding would most
strongly support iron deficiency as the cause of this anemia?
A. Increased serum ferritin
B. Decreased total iron-binding capacity
C. Increased red cell distribution width
D. Increased mean corpuscular hemoglobin
Iron deficiency commonly produces microcytosis with increased RDW because newly produced
cells become progressively smaller as iron stores are depleted.
2. A peripheral blood smear demonstrates numerous neutrophils with more than five
nuclear lobes. Which condition is most strongly associated with this finding?
A. Vitamin B12 deficiency
B. Acute blood loss
C. Iron deficiency
D. Hereditary spherocytosis
Hypersegmented neutrophils are characteristic of megaloblastic anemia caused by impaired
DNA synthesis, particularly vitamin B12 or folate deficiency.
3. A blood specimen submitted for potassium testing is visibly hemolyzed. The
potassium result is markedly increased, while the patient has no clinical evidence of
hyperkalemia. What is the most appropriate laboratory action?
A. Report the result immediately
B. Dilute the specimen and repeat the test
C. Add an anticoagulant and retest
D. Request a new specimen
Hemolysis releases intracellular potassium from erythrocytes and can produce a falsely
increased result. A new properly collected specimen is appropriate when the integrity of the
original sample is compromised.
4. Which white blood cell is normally the most abundant leukocyte in the peripheral
blood of a healthy adult?
A. Lymphocyte
B. Neutrophil
C. Monocyte
D. Eosinophil
,Neutrophils normally constitute the largest proportion of circulating leukocytes in healthy
adults and are central to the innate immune response.
5. A patient with suspected hereditary spherocytosis has a peripheral smear showing
numerous small, dense erythrocytes without central pallor. Which additional test is
most useful for supporting the diagnosis?
A. Osmotic fragility or eosin-5-maleimide binding testing
B. Sickling solubility testing
C. Direct antiglobulin testing only
D. Hemoglobin electrophoresis
Spherocytes are characteristic of hereditary spherocytosis, and eosin-5-maleimide binding or
appropriate osmotic fragility testing can provide supportive evidence.
6. A patient has a prolonged PT and normal aPTT. Which coagulation factor
deficiency is most likely to produce this pattern?
A. Factor VIII
B. Factor IX
C. Factor XI
D. Factor VII
Factor VII belongs to the extrinsic pathway and is assessed primarily by PT. An isolated
prolonged PT therefore suggests a factor VII problem or another cause selectively affecting
the extrinsic pathway.
7. A patient receiving unfractionated heparin therapy requires laboratory monitoring.
Which test is traditionally used to monitor its anticoagulant effect?
A. PT/INR
B. aPTT
C. Bleeding time
D. Fibrinogen assay
The activated partial thromboplastin time is commonly used to monitor unfractionated
heparin, although anti-Xa testing may be preferred in specific clinical circumstances.
8. A prolonged aPTT fails to correct after a 1:1 mixture of patient plasma with normal
pooled plasma. What does this result most strongly suggest?
A. Factor deficiency
B. Specimen hemolysis
C. An inhibitor
D. Excess fibrinogen
Failure of correction in a mixing study suggests an inhibitor, such as a specific factor inhibitor
or lupus anticoagulant, rather than a simple factor deficiency.
, 9. Which organism is characterized by gram-positive cocci arranged in clusters and
production of catalase?
A. Streptococcus pyogenes
B. Enterococcus faecalis
C. Staphylococcus aureus
D. Streptococcus pneumoniae
Staphylococci are gram-positive cocci arranged in clusters and are catalase positive. S. aureus
is distinguished from many other staphylococci by additional characteristics such as coagulase
positivity.
10. A wound culture yields gram-positive cocci in chains that are catalase negative and
bile-esculin positive. Which organism is most likely?
A. Enterococcus faecalis
B. Staphylococcus epidermidis
C. Micrococcus luteus
D. Staphylococcus aureus
Enterococcus species are catalase-negative gram-positive cocci that can grow in bile and
hydrolyze esculin.
11. A urine culture from a symptomatic patient grows a lactose-fermenting gram-
negative rod that is indole positive and produces a characteristic metallic sheen on
certain differential media. Which organism is most likely?
A. Proteus mirabilis
B. Escherichia coli
C. Pseudomonas aeruginosa
D. Salmonella enterica
Escherichia coli is a common urinary pathogen and typically produces lactose fermentation,
indole positivity, and characteristic growth on appropriate selective and differential media.
12. A gram-negative rod from a respiratory specimen produces a blue-green pigment
and has a fruity odor. Which organism is most likely?
A. Klebsiella pneumoniae
B. Escherichia coli
C. Pseudomonas aeruginosa
D. Haemophilus influenzae
Pseudomonas aeruginosa can produce pyocyanin, producing a blue-green appearance, and
may have a distinctive fruity or grape-like odor.
13. A blood culture becomes positive and demonstrates gram-positive cocci in clusters.
The organism is catalase positive and coagulase positive. Which identification is
most appropriate?
, A. Staphylococcus aureus
B. Staphylococcus epidermidis
C. Streptococcus agalactiae
D. Enterococcus faecium
The combination of gram-positive cocci in clusters, catalase positivity, and coagulase
positivity strongly supports Staphylococcus aureus.
14. Which organism is most characteristically associated with a positive CAMP test?
A. Streptococcus pyogenes
B. Streptococcus agalactiae
C. Streptococcus pneumoniae
D. Enterococcus faecalis
Streptococcus agalactiae, or group B Streptococcus, characteristically produces a positive
CAMP reaction.
15. A beta-hemolytic Streptococcus isolate is PYR positive and grows in bile-esculin
medium. Which organism is most likely?
A. Streptococcus pyogenes
B. Streptococcus agalactiae
C. Enterococcus species
D. Streptococcus pneumoniae
Enterococci are characteristically PYR positive and bile-esculin positive, helping distinguish
them from many other streptococci.
16. A cerebrospinal fluid specimen from a neonate demonstrates small gram-negative
coccobacilli that require X and V factors for growth. Which organism should be
suspected?
A. Haemophilus influenzae
B. Bordetella pertussis
C. Neisseria meningitidis
D. Moraxella catarrhalis
Haemophilus influenzae requires hemin (X factor) and NAD (V factor) for growth and can
cause serious invasive disease, including meningitis.
17. A patient develops profuse watery diarrhea after receiving broad-spectrum
antibiotics. Stool testing is requested for a toxin-producing organism. Which
pathogen is the primary concern?
A. Shigella sonnei
B. Campylobacter jejuni
C. Clostridioides difficile
D. Vibrio cholerae
PRACTICE Q&A 2026/2027 | A+ GRADED |
COMPREHENSIVE EXAM GUIDE 2026&2027
1. A patient’s complete blood count shows a hemoglobin concentration of 7.8 g/dL,
hematocrit of 23%, and MCV of 72 fL. Which additional finding would most
strongly support iron deficiency as the cause of this anemia?
A. Increased serum ferritin
B. Decreased total iron-binding capacity
C. Increased red cell distribution width
D. Increased mean corpuscular hemoglobin
Iron deficiency commonly produces microcytosis with increased RDW because newly produced
cells become progressively smaller as iron stores are depleted.
2. A peripheral blood smear demonstrates numerous neutrophils with more than five
nuclear lobes. Which condition is most strongly associated with this finding?
A. Vitamin B12 deficiency
B. Acute blood loss
C. Iron deficiency
D. Hereditary spherocytosis
Hypersegmented neutrophils are characteristic of megaloblastic anemia caused by impaired
DNA synthesis, particularly vitamin B12 or folate deficiency.
3. A blood specimen submitted for potassium testing is visibly hemolyzed. The
potassium result is markedly increased, while the patient has no clinical evidence of
hyperkalemia. What is the most appropriate laboratory action?
A. Report the result immediately
B. Dilute the specimen and repeat the test
C. Add an anticoagulant and retest
D. Request a new specimen
Hemolysis releases intracellular potassium from erythrocytes and can produce a falsely
increased result. A new properly collected specimen is appropriate when the integrity of the
original sample is compromised.
4. Which white blood cell is normally the most abundant leukocyte in the peripheral
blood of a healthy adult?
A. Lymphocyte
B. Neutrophil
C. Monocyte
D. Eosinophil
,Neutrophils normally constitute the largest proportion of circulating leukocytes in healthy
adults and are central to the innate immune response.
5. A patient with suspected hereditary spherocytosis has a peripheral smear showing
numerous small, dense erythrocytes without central pallor. Which additional test is
most useful for supporting the diagnosis?
A. Osmotic fragility or eosin-5-maleimide binding testing
B. Sickling solubility testing
C. Direct antiglobulin testing only
D. Hemoglobin electrophoresis
Spherocytes are characteristic of hereditary spherocytosis, and eosin-5-maleimide binding or
appropriate osmotic fragility testing can provide supportive evidence.
6. A patient has a prolonged PT and normal aPTT. Which coagulation factor
deficiency is most likely to produce this pattern?
A. Factor VIII
B. Factor IX
C. Factor XI
D. Factor VII
Factor VII belongs to the extrinsic pathway and is assessed primarily by PT. An isolated
prolonged PT therefore suggests a factor VII problem or another cause selectively affecting
the extrinsic pathway.
7. A patient receiving unfractionated heparin therapy requires laboratory monitoring.
Which test is traditionally used to monitor its anticoagulant effect?
A. PT/INR
B. aPTT
C. Bleeding time
D. Fibrinogen assay
The activated partial thromboplastin time is commonly used to monitor unfractionated
heparin, although anti-Xa testing may be preferred in specific clinical circumstances.
8. A prolonged aPTT fails to correct after a 1:1 mixture of patient plasma with normal
pooled plasma. What does this result most strongly suggest?
A. Factor deficiency
B. Specimen hemolysis
C. An inhibitor
D. Excess fibrinogen
Failure of correction in a mixing study suggests an inhibitor, such as a specific factor inhibitor
or lupus anticoagulant, rather than a simple factor deficiency.
, 9. Which organism is characterized by gram-positive cocci arranged in clusters and
production of catalase?
A. Streptococcus pyogenes
B. Enterococcus faecalis
C. Staphylococcus aureus
D. Streptococcus pneumoniae
Staphylococci are gram-positive cocci arranged in clusters and are catalase positive. S. aureus
is distinguished from many other staphylococci by additional characteristics such as coagulase
positivity.
10. A wound culture yields gram-positive cocci in chains that are catalase negative and
bile-esculin positive. Which organism is most likely?
A. Enterococcus faecalis
B. Staphylococcus epidermidis
C. Micrococcus luteus
D. Staphylococcus aureus
Enterococcus species are catalase-negative gram-positive cocci that can grow in bile and
hydrolyze esculin.
11. A urine culture from a symptomatic patient grows a lactose-fermenting gram-
negative rod that is indole positive and produces a characteristic metallic sheen on
certain differential media. Which organism is most likely?
A. Proteus mirabilis
B. Escherichia coli
C. Pseudomonas aeruginosa
D. Salmonella enterica
Escherichia coli is a common urinary pathogen and typically produces lactose fermentation,
indole positivity, and characteristic growth on appropriate selective and differential media.
12. A gram-negative rod from a respiratory specimen produces a blue-green pigment
and has a fruity odor. Which organism is most likely?
A. Klebsiella pneumoniae
B. Escherichia coli
C. Pseudomonas aeruginosa
D. Haemophilus influenzae
Pseudomonas aeruginosa can produce pyocyanin, producing a blue-green appearance, and
may have a distinctive fruity or grape-like odor.
13. A blood culture becomes positive and demonstrates gram-positive cocci in clusters.
The organism is catalase positive and coagulase positive. Which identification is
most appropriate?
, A. Staphylococcus aureus
B. Staphylococcus epidermidis
C. Streptococcus agalactiae
D. Enterococcus faecium
The combination of gram-positive cocci in clusters, catalase positivity, and coagulase
positivity strongly supports Staphylococcus aureus.
14. Which organism is most characteristically associated with a positive CAMP test?
A. Streptococcus pyogenes
B. Streptococcus agalactiae
C. Streptococcus pneumoniae
D. Enterococcus faecalis
Streptococcus agalactiae, or group B Streptococcus, characteristically produces a positive
CAMP reaction.
15. A beta-hemolytic Streptococcus isolate is PYR positive and grows in bile-esculin
medium. Which organism is most likely?
A. Streptococcus pyogenes
B. Streptococcus agalactiae
C. Enterococcus species
D. Streptococcus pneumoniae
Enterococci are characteristically PYR positive and bile-esculin positive, helping distinguish
them from many other streptococci.
16. A cerebrospinal fluid specimen from a neonate demonstrates small gram-negative
coccobacilli that require X and V factors for growth. Which organism should be
suspected?
A. Haemophilus influenzae
B. Bordetella pertussis
C. Neisseria meningitidis
D. Moraxella catarrhalis
Haemophilus influenzae requires hemin (X factor) and NAD (V factor) for growth and can
cause serious invasive disease, including meningitis.
17. A patient develops profuse watery diarrhea after receiving broad-spectrum
antibiotics. Stool testing is requested for a toxin-producing organism. Which
pathogen is the primary concern?
A. Shigella sonnei
B. Campylobacter jejuni
C. Clostridioides difficile
D. Vibrio cholerae
