CALIFORNIA CLINICAL LABORATORY SCIENTIST
(CLS)
LICENSING EXAMINATION
PRACTICE TEST
2026–2027 Testing Cycle
1. A clinical laboratory scientist is preparing a series of dilutions for a glucose tolerance test. The
stock glucose standard is 2000 mg/dL. What volume of stock is required to prepare 500 mL of a
200 mg/dL working standard?
A) 5 mL
B) 10 mL
C) 25 mL
D) 50 mL
Correct Answer: D
Rationale: Using C1V1 = C2V2, (2000 mg/dL)(V1) = (200 mg/dL)(500 mL) → V1 = 50 mL. The
other options result from miscalculation of the dilution factor or incorrect unit conversion.
2. Which of the following blood collection tubes is the most appropriate for obtaining serum for
a comprehensive metabolic panel?
A) Lavender top (EDTA)
B) Light blue top (sodium citrate)
C) Gold top (serum separator with clot activator and gel)
D) Green top (sodium heparin)
Correct Answer: C
Rationale: Serum separator tubes allow blood to clot and then separate serum via gel barrier;
,they are suitable for most chemistry panels. Lavender top is used for whole blood hematology,
light blue for coagulation studies, and green top yields plasma rather than serum.
3. In brightfield microscopy, what is the primary purpose of the condenser?
A) To magnify the image after the objective lens
B) To provide initial light filtration for fluorescence
C) To focus light onto the specimen to improve resolution
D) To protect the objective lens from immersion oil
Correct Answer: C
Rationale: The condenser collects and focuses light from the illuminator onto the specimen,
controlling the cone of light that enters the objective to enhance resolution and contrast.
Magnification is a function of objective and ocular lenses, not the condenser.
4. A manual white blood cell count yields 45 cells counted in the four corner squares of a
Neubauer hemocytometer using a 1:20 dilution. What is the WBC count per microliter?
A) 2.25 x 10³/µL
B) 4.5 x 10³/µL
C) 9.0 x 10³/µL
D) 22.5 x 10³/µL
Correct Answer: B
*Rationale: WBC count = (cells counted / number of squares) × dilution factor × depth factor.
For 4 squares, volume is 0.1 mm² × 0.1 mm depth × 4 = 0.4 mm³? Actually standard formula:
cells/µL = (cells counted × dilution factor) / (area counted × depth). Area 4 mm² (4 squares each
1 mm²) × 0.1 mm depth = 0.4 µL. So count = (45 × 20) / 0.4 = .4 = 2250, but wait 45 cells
,in 4 squares, dilution 1:20, factor 20; volume 0.4 µL, so cells/µL = (45 × 20) / 0.4 = .4 =
2250/µL = 2.25 × 10³/µL. I gave answer B as 4.5 x 10³, that is incorrect. Recalculate: Total
volume of 4 corner squares (each 1 mm × 1 mm × 0.1 mm) = 4 × 0.1 mm³ = 0.4 mm³ = 0.4 µL.
Count 45 cells in 0.4 µL of diluted sample. Dilution 1:20 means 1 part blood + 19 parts diluent.
The count in diluted sample is 45/0.4 µL = 112.5 cells/µL diluted. Undiluted = 112.5 × 20 = 2250
cells/µL = 2.25 × 10³/µL. So correct answer is A. I mistakenly set answer B. I need to correct.
Let's make sure the question's math is right. I'll recalc: cells/µL = (cells counted / volume in µL)
× dilution factor. Volume = 4 squares × (1 mm × 1 mm × 0.1 mm) = 0.4 mm³ = 0.4 µL. So
diluted concentration = 45/0.4 = 112.5/µL. Multiply by dilution factor 20 = 2250/µL = 2.25 ×
10³/µL. So correct answer A. I'll adjust answer and rationale. Rationale: WBC count = (cells
counted × dilution) / (area counted × depth) = (45 × 20) / (4 × 0.1) = .4 = 2,250/µL.
Options B, C, D miscalculate volume or dilution factor. So I'll change correct answer to A. I'll
update question 4 accordingly. I'll do that in final output. Meanwhile continue.
4. A manual white blood cell count yields 45 cells counted in the four corner squares of a
Neubauer hemocytometer using a 1:20 dilution. What is the WBC count per microliter?
A) 2.25 × 10³/µL
B) 4.5 × 10³/µL
C) 9.0 × 10³/µL
D) 22.5 × 10³/µL
Correct Answer: A
Rationale: WBC count/µL = (cells counted × dilution) / (area counted [mm²] × depth [mm]).
Area 4 squares = 4 mm², depth 0.1 mm, volume 0.4 µL. Count = (45 × 20) / 0.4 = 2250/µL =
, 2.25 × 10³/µL. Dividing by 0.4 correctly yields 2.25; other answers invert the volume factor or
misplace decimal.
5. Which immunoglobulin class is primarily responsible for mediating allergic reactions and
defense against parasitic infections?
A) IgA
B) IgD
C) IgE
D) IgM
Correct Answer: C
Rationale: IgE binds to mast cells and basophils, triggering degranulation and release of
histamine in allergic responses, and plays a key role in defense against helminthic parasites. IgA
is mucosal, IgD is a B-cell receptor, IgM is primary response and isohemagglutinins.
6. A patient’s PT is 35 seconds (reference range 11–14 sec), PTT is 60 seconds (reference range
25–35 sec), and platelet count is 250,000/µL. These results are most consistent with:
A) Vitamin K deficiency
B) Hemophilia A
C) Disseminated intravascular coagulation (DIC) with consumption
D) Lupus anticoagulant
Correct Answer: A
Rationale: Prolonged PT and PTT with normal platelet count suggest deficiency of vitamin K-
dependent factors (II, VII, IX, X). Hemophilia A typically shows prolonged PTT only, DIC often
has decreased platelets, lupus anticoagulant prolongs PTT but PT is usually normal or
(CLS)
LICENSING EXAMINATION
PRACTICE TEST
2026–2027 Testing Cycle
1. A clinical laboratory scientist is preparing a series of dilutions for a glucose tolerance test. The
stock glucose standard is 2000 mg/dL. What volume of stock is required to prepare 500 mL of a
200 mg/dL working standard?
A) 5 mL
B) 10 mL
C) 25 mL
D) 50 mL
Correct Answer: D
Rationale: Using C1V1 = C2V2, (2000 mg/dL)(V1) = (200 mg/dL)(500 mL) → V1 = 50 mL. The
other options result from miscalculation of the dilution factor or incorrect unit conversion.
2. Which of the following blood collection tubes is the most appropriate for obtaining serum for
a comprehensive metabolic panel?
A) Lavender top (EDTA)
B) Light blue top (sodium citrate)
C) Gold top (serum separator with clot activator and gel)
D) Green top (sodium heparin)
Correct Answer: C
Rationale: Serum separator tubes allow blood to clot and then separate serum via gel barrier;
,they are suitable for most chemistry panels. Lavender top is used for whole blood hematology,
light blue for coagulation studies, and green top yields plasma rather than serum.
3. In brightfield microscopy, what is the primary purpose of the condenser?
A) To magnify the image after the objective lens
B) To provide initial light filtration for fluorescence
C) To focus light onto the specimen to improve resolution
D) To protect the objective lens from immersion oil
Correct Answer: C
Rationale: The condenser collects and focuses light from the illuminator onto the specimen,
controlling the cone of light that enters the objective to enhance resolution and contrast.
Magnification is a function of objective and ocular lenses, not the condenser.
4. A manual white blood cell count yields 45 cells counted in the four corner squares of a
Neubauer hemocytometer using a 1:20 dilution. What is the WBC count per microliter?
A) 2.25 x 10³/µL
B) 4.5 x 10³/µL
C) 9.0 x 10³/µL
D) 22.5 x 10³/µL
Correct Answer: B
*Rationale: WBC count = (cells counted / number of squares) × dilution factor × depth factor.
For 4 squares, volume is 0.1 mm² × 0.1 mm depth × 4 = 0.4 mm³? Actually standard formula:
cells/µL = (cells counted × dilution factor) / (area counted × depth). Area 4 mm² (4 squares each
1 mm²) × 0.1 mm depth = 0.4 µL. So count = (45 × 20) / 0.4 = .4 = 2250, but wait 45 cells
,in 4 squares, dilution 1:20, factor 20; volume 0.4 µL, so cells/µL = (45 × 20) / 0.4 = .4 =
2250/µL = 2.25 × 10³/µL. I gave answer B as 4.5 x 10³, that is incorrect. Recalculate: Total
volume of 4 corner squares (each 1 mm × 1 mm × 0.1 mm) = 4 × 0.1 mm³ = 0.4 mm³ = 0.4 µL.
Count 45 cells in 0.4 µL of diluted sample. Dilution 1:20 means 1 part blood + 19 parts diluent.
The count in diluted sample is 45/0.4 µL = 112.5 cells/µL diluted. Undiluted = 112.5 × 20 = 2250
cells/µL = 2.25 × 10³/µL. So correct answer is A. I mistakenly set answer B. I need to correct.
Let's make sure the question's math is right. I'll recalc: cells/µL = (cells counted / volume in µL)
× dilution factor. Volume = 4 squares × (1 mm × 1 mm × 0.1 mm) = 0.4 mm³ = 0.4 µL. So
diluted concentration = 45/0.4 = 112.5/µL. Multiply by dilution factor 20 = 2250/µL = 2.25 ×
10³/µL. So correct answer A. I'll adjust answer and rationale. Rationale: WBC count = (cells
counted × dilution) / (area counted × depth) = (45 × 20) / (4 × 0.1) = .4 = 2,250/µL.
Options B, C, D miscalculate volume or dilution factor. So I'll change correct answer to A. I'll
update question 4 accordingly. I'll do that in final output. Meanwhile continue.
4. A manual white blood cell count yields 45 cells counted in the four corner squares of a
Neubauer hemocytometer using a 1:20 dilution. What is the WBC count per microliter?
A) 2.25 × 10³/µL
B) 4.5 × 10³/µL
C) 9.0 × 10³/µL
D) 22.5 × 10³/µL
Correct Answer: A
Rationale: WBC count/µL = (cells counted × dilution) / (area counted [mm²] × depth [mm]).
Area 4 squares = 4 mm², depth 0.1 mm, volume 0.4 µL. Count = (45 × 20) / 0.4 = 2250/µL =
, 2.25 × 10³/µL. Dividing by 0.4 correctly yields 2.25; other answers invert the volume factor or
misplace decimal.
5. Which immunoglobulin class is primarily responsible for mediating allergic reactions and
defense against parasitic infections?
A) IgA
B) IgD
C) IgE
D) IgM
Correct Answer: C
Rationale: IgE binds to mast cells and basophils, triggering degranulation and release of
histamine in allergic responses, and plays a key role in defense against helminthic parasites. IgA
is mucosal, IgD is a B-cell receptor, IgM is primary response and isohemagglutinins.
6. A patient’s PT is 35 seconds (reference range 11–14 sec), PTT is 60 seconds (reference range
25–35 sec), and platelet count is 250,000/µL. These results are most consistent with:
A) Vitamin K deficiency
B) Hemophilia A
C) Disseminated intravascular coagulation (DIC) with consumption
D) Lupus anticoagulant
Correct Answer: A
Rationale: Prolonged PT and PTT with normal platelet count suggest deficiency of vitamin K-
dependent factors (II, VII, IX, X). Hemophilia A typically shows prolonged PTT only, DIC often
has decreased platelets, lupus anticoagulant prolongs PTT but PT is usually normal or
