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AMT MEDICAL LABORATORY SCIENTIST (MLS) MIDTERM EXAMINATION
Complete Practice Test Bank – 75 Questions & Detailed Rationales
Based on AMT MLS Exam Content Guidelines – Latest 2026-2027 Edition
EXAM INSTRUCTIONS
- This midterm examination consists of 75 multiple-choice questions.
- Each question has four answer choices (A–D).
- Select the single best answer for each question.
- Questions are based on the AMT Medical Laboratory Scientist (MLS)
Certification Examcontent guidelines.
- Time suggested: 90 minutes** (approximately 1.2 minutes per question).
- Topics covered: Clinical Chemistry, Hematology, Coagulation,
Immunohematology/Blood Bank, Microbiology, Immunology/Serology,
Urinalysis/Body Fluids, and Laboratory Operations.
Question 1
A 52-year-old male patient with a history of diabetes mellitus and
hypertension is admitted to the hospital with acute kidney injury.
Laboratory tests reveal a serum creatinine of 3.8 mg/dL and a blood urea
nitrogen (BUN) of 85 mg/dL. The calculated BUN-to-creatinine ratio is 22:1.
Which of the following correctly interprets this ratio, and what is the most
likely underlying cause of the patient's acute kidney injury?**
,2
A) The ratio is consistent with prerenal azotemia, indicating decreased
renal perfusion due to hypovolemia, heart failure, or sepsis
B) The ratio is consistent with intrinsic renal azotemia, indicating damage
to the renal tubules or glomeruli
C) The ratio is consistent with postrenal azotemia, indicating obstruction of
the urinary tract
D) The ratio is within the normal reference range and provides no
additional diagnostic information
Answer: A
Rationale:The BUN-to-creatinine ratio is calculated by dividing the BUN
concentration (in mg/dL) by the serum creatinine concentration (in mg/dL).
A normal ratio is approximately 10:1 to 15:1 (in mass units) or 10:1 to 20:1
depending on laboratory reference ranges. A BUN-to-creatinine ratio of
22:1 is elevated. In prerenal azotemia, the ratio is typically > 20:1 because
the kidneys respond to decreased perfusion by increasing reabsorption of
urea in the proximal tubule, leading to a disproportionate increase in BUN
relative to creatinine. Prerenal azotemia can be caused by hypovolemia
(e.g., dehydration, hemorrhage), decreased cardiac output (e.g., heart
failure), or decreased systemic vascular resistance (e.g., sepsis). Intrinsic
renal azotemia (Option B) is characterized by a ratio of < 15:1 because both
BUN and creatinine increase proportionally due to decreased glomerular
filtration. Postrenal azotemia (Option C) is caused by urinary tract
obstruction and may have an elevated ratio, but it is less common and
,3
usually associated with other findings. Option D is incorrect because a ratio
of 22:1 is elevated and provides important diagnostic information.
Question 2
A technologist is performing a quality control assessment on a new lot
number of reagent for an enzymatic assay measuring serum lactate
dehydrogenase (LDH). The technologist runs 20 replicates of a control
sample and calculates the mean and standard deviation. Which of the
following statistical measures is most appropriate for assessing the
imprecision of the assay, and what is the formula for its calculation?**
A) Coefficient of variation (CV), calculated as (standard deviation / mean) ×
100%
B) Standard deviation (SD), calculated as the square root of the variance
C) Variance, calculated as the average of the squared differences from the
mean
D) Range, calculated as the difference between the highest and lowest
values
Answer: A
**Rationale:** The coefficient of variation (CV) is a measure of relative
variability that expresses the standard deviation as a percentage of the
mean. It is the most appropriate measure for assessing the imprecision
, 4
(random error) of an assay because it allows comparison of precision across
different concentrations and analytes. The formula for CV is: CV = (SD /
mean) × 100%. A lower CV indicates better precision. Option B describes
the standard deviation, which is a measure of absolute variability but does
not allow comparison across different means. Option C describes the
variance, which is the square of the standard deviation and is less
commonly used in laboratory quality control. Option D describes the range,
which is a crude measure of variability that is highly sensitive to outliers
and does not provide information about the distribution of values.
Question 3
A 45-year-old female patient presents with symptoms of fatigue, weight
gain, cold intolerance, and constipation. Laboratory tests reveal a serum
total thyroxine (T4) of 2.5 µg/dL (reference range: 4.5-12.5 µg/dL) and a
serum thyroid-stimulating hormone (TSH) of 12.0 µIU/mL (reference range:
0.4-4.0 µIU/mL). Which of the following correctly interprets the
relationship between TSH and T4 in this patient, and what is the most likely
diagnosis?**
A) Primary hypothyroidism, characterized by low T4 and elevated TSH due
to thyroid gland failure and loss of negative feedback on the pituitary
B) Secondary hypothyroidism, characterized by low T4 and low TSH due to
pituitary gland failure
C) Tertiary hypothyroidism, characterized by low T4 and low TSH due to
hypothalamic failure
AMT MEDICAL LABORATORY SCIENTIST (MLS) MIDTERM EXAMINATION
Complete Practice Test Bank – 75 Questions & Detailed Rationales
Based on AMT MLS Exam Content Guidelines – Latest 2026-2027 Edition
EXAM INSTRUCTIONS
- This midterm examination consists of 75 multiple-choice questions.
- Each question has four answer choices (A–D).
- Select the single best answer for each question.
- Questions are based on the AMT Medical Laboratory Scientist (MLS)
Certification Examcontent guidelines.
- Time suggested: 90 minutes** (approximately 1.2 minutes per question).
- Topics covered: Clinical Chemistry, Hematology, Coagulation,
Immunohematology/Blood Bank, Microbiology, Immunology/Serology,
Urinalysis/Body Fluids, and Laboratory Operations.
Question 1
A 52-year-old male patient with a history of diabetes mellitus and
hypertension is admitted to the hospital with acute kidney injury.
Laboratory tests reveal a serum creatinine of 3.8 mg/dL and a blood urea
nitrogen (BUN) of 85 mg/dL. The calculated BUN-to-creatinine ratio is 22:1.
Which of the following correctly interprets this ratio, and what is the most
likely underlying cause of the patient's acute kidney injury?**
,2
A) The ratio is consistent with prerenal azotemia, indicating decreased
renal perfusion due to hypovolemia, heart failure, or sepsis
B) The ratio is consistent with intrinsic renal azotemia, indicating damage
to the renal tubules or glomeruli
C) The ratio is consistent with postrenal azotemia, indicating obstruction of
the urinary tract
D) The ratio is within the normal reference range and provides no
additional diagnostic information
Answer: A
Rationale:The BUN-to-creatinine ratio is calculated by dividing the BUN
concentration (in mg/dL) by the serum creatinine concentration (in mg/dL).
A normal ratio is approximately 10:1 to 15:1 (in mass units) or 10:1 to 20:1
depending on laboratory reference ranges. A BUN-to-creatinine ratio of
22:1 is elevated. In prerenal azotemia, the ratio is typically > 20:1 because
the kidneys respond to decreased perfusion by increasing reabsorption of
urea in the proximal tubule, leading to a disproportionate increase in BUN
relative to creatinine. Prerenal azotemia can be caused by hypovolemia
(e.g., dehydration, hemorrhage), decreased cardiac output (e.g., heart
failure), or decreased systemic vascular resistance (e.g., sepsis). Intrinsic
renal azotemia (Option B) is characterized by a ratio of < 15:1 because both
BUN and creatinine increase proportionally due to decreased glomerular
filtration. Postrenal azotemia (Option C) is caused by urinary tract
obstruction and may have an elevated ratio, but it is less common and
,3
usually associated with other findings. Option D is incorrect because a ratio
of 22:1 is elevated and provides important diagnostic information.
Question 2
A technologist is performing a quality control assessment on a new lot
number of reagent for an enzymatic assay measuring serum lactate
dehydrogenase (LDH). The technologist runs 20 replicates of a control
sample and calculates the mean and standard deviation. Which of the
following statistical measures is most appropriate for assessing the
imprecision of the assay, and what is the formula for its calculation?**
A) Coefficient of variation (CV), calculated as (standard deviation / mean) ×
100%
B) Standard deviation (SD), calculated as the square root of the variance
C) Variance, calculated as the average of the squared differences from the
mean
D) Range, calculated as the difference between the highest and lowest
values
Answer: A
**Rationale:** The coefficient of variation (CV) is a measure of relative
variability that expresses the standard deviation as a percentage of the
mean. It is the most appropriate measure for assessing the imprecision
, 4
(random error) of an assay because it allows comparison of precision across
different concentrations and analytes. The formula for CV is: CV = (SD /
mean) × 100%. A lower CV indicates better precision. Option B describes
the standard deviation, which is a measure of absolute variability but does
not allow comparison across different means. Option C describes the
variance, which is the square of the standard deviation and is less
commonly used in laboratory quality control. Option D describes the range,
which is a crude measure of variability that is highly sensitive to outliers
and does not provide information about the distribution of values.
Question 3
A 45-year-old female patient presents with symptoms of fatigue, weight
gain, cold intolerance, and constipation. Laboratory tests reveal a serum
total thyroxine (T4) of 2.5 µg/dL (reference range: 4.5-12.5 µg/dL) and a
serum thyroid-stimulating hormone (TSH) of 12.0 µIU/mL (reference range:
0.4-4.0 µIU/mL). Which of the following correctly interprets the
relationship between TSH and T4 in this patient, and what is the most likely
diagnosis?**
A) Primary hypothyroidism, characterized by low T4 and elevated TSH due
to thyroid gland failure and loss of negative feedback on the pituitary
B) Secondary hypothyroidism, characterized by low T4 and low TSH due to
pituitary gland failure
C) Tertiary hypothyroidism, characterized by low T4 and low TSH due to
hypothalamic failure
