Welcome to Part 55 of the ASCP MLS Exam Practice Series, focusing on Clinical Chemistry and Quality Control. This final section brings together essential laboratory principles that ensure accuracy, precision, and reliability of biochemical testing. It covers clinical chemistry instrumentation, automation, calibration, and statistical quality control — all critical for producing trustworthy laboratory results in patient care.
📘 Key Topics Covered
- Fundamentals of clinical chemistry instrumentation
- Spectrophotometry, electrophoresis, and chromatography
- Ion-selective electrodes (ISE) and immunoassay techniques
- Automation and workflow in clinical laboratories
- Calibration, standardization, and reagent management
- Quality assurance (QA) and quality control (QC) concepts
- Internal and external QC programs
- Westgard rules and Levey-Jennings chart interpretation
- Reference ranges and analytical performance criteria
- Laboratory safety, error prevention, and documentation
🧠 Learning Objectives
By the end of this part, you should be able to:
- Understand the working principles of key clinical chemistry instruments.
- Apply quality control procedures to ensure analytical reliability.
- Interpret QC charts and identify analytical errors.
- Relate laboratory performance to patient safety and accreditation standards.
60 MCQs (4241 – 4300):
- Enzymes are best described as:
a) Structural proteins
b) Biological catalysts that speed up chemical reactions
c) Hormones that regulate metabolism
d) Vitamins that activate reactions - The protein part of an enzyme without its cofactor is called a:
a) Holoenzyme
b) Apoenzyme
c) Coenzyme
d) Prosthetic group - A cofactor that is loosely bound to an enzyme and participates in catalysis is known as a:
a) Metal ion
b) Coenzyme
c) Apoenzyme
d) Inhibitor - The complete, active form of an enzyme is called a:
a) Holoenzyme
b) Apoenzyme
c) Isoenzyme
d) Substrate - Enzymes act by:
a) Increasing activation energy
b) Decreasing activation energy
c) Changing reaction equilibrium
d) Increasing product concentration - The substance upon which an enzyme acts is the:
a) Product
b) Inhibitor
c) Substrate
d) Coenzyme - The specific region on an enzyme where the substrate binds is the:
a) Regulatory site
b) Active site
c) Allosteric site
d) Cofactor site - Enzyme activity is most affected by:
a) pH, temperature, and substrate concentration
b) Light intensity
c) Osmotic pressure only
d) Radiation exposure - The relationship between enzyme velocity and substrate concentration is described by:
a) Henderson–Hasselbalch equation
b) Michaelis–Menten equation
c) Beer–Lambert law
d) Lineweaver–Burk equation - The substrate concentration at which an enzyme achieves half its maximum velocity (Vmax) is called:
a) Vmax
b) Km (Michaelis constant)
c) Ki
d) pKa - An enzyme that catalyzes oxidation-reduction reactions belongs to the class:
a) Oxidoreductases
b) Transferases
c) Hydrolases
d) Ligases - Enzymes that transfer functional groups between molecules are called:
a) Isomerases
b) Transferases
c) Hydrolases
d) Lyases - Enzymes that catalyze the breakdown of molecules using water are:
a) Hydrolases
b) Lyases
c) Isomerases
d) Oxidoreductases - Isoenzymes are:
a) Chemically identical enzymes with different activities
b) Different forms of an enzyme that catalyze the same reaction
c) Enzymes that inhibit each other
d) Non-protein cofactors - Which enzyme is most specific for myocardial infarction?
a) AST
b) LDH
c) CK-MB
d) ALT - The earliest cardiac marker to rise after a heart attack is:
a) CK-MB
b) Troponin
c) Myoglobin
d) LDH - Troponin is preferred over CK-MB for myocardial infarction diagnosis because it:
a) Rises earlier and returns to normal faster
b) Rises later but stays elevated longer
c) Is not cardiac-specific
d) Is unstable in serum - LDH (lactate dehydrogenase) catalyzes the interconversion of:
a) Glucose and pyruvate
b) Pyruvate and lactate
c) Creatine and creatinine
d) Alanine and pyruvate - The total LDH enzyme is composed of how many subunits?
a) 2
b) 3
c) 4
d) 5 - LDH isoenzyme LD1 > LD2 (flipped pattern) indicates:
a) Liver disease
b) Myocardial infarction
c) Muscle injury
d) Hemolysis - ALT (alanine aminotransferase) is primarily found in the:
a) Heart
b) Liver
c) Muscle
d) Brain - AST (aspartate aminotransferase) is found in significant amounts in the:
a) Brain and kidney
b) Liver and heart
c) Pancreas and intestine
d) Bone and cartilage - Which enzyme is most specific for hepatocellular damage?
a) ALP
b) ALT
c) GGT
d) LDH - Alkaline phosphatase (ALP) is markedly increased in:
a) Myocardial infarction
b) Obstructive jaundice and bone disease
c) Liver failure only
d) Diabetes mellitus - Gamma-glutamyl transferase (GGT) is a sensitive marker for:
a) Muscle damage
b) Alcoholic liver disease
c) Thyroid disease
d) Kidney function - Amylase and lipase are primarily used to diagnose:
a) Myocardial infarction
b) Pancreatitis
c) Hepatitis
d) Muscle injury - Elevated serum amylase with normal lipase suggests:
a) Acute pancreatitis
b) Salivary gland disorder
c) Hepatitis
d) Renal failure - Creatine kinase (CK) exists as three isoenzymes. The cardiac-specific one is:
a) CK-MM
b) CK-MB
c) CK-BB
d) CK-1 - Acid phosphatase (ACP) was historically used to diagnose:
a) Bone disease
b) Prostate cancer
c) Liver dysfunction
d) Pancreatitis - The enzyme cholinesterase is clinically important in assessing:
a) Renal function
b) Pesticide poisoning or anesthesia sensitivity
c) Bone metabolism
d) Pancreatic function - 1. One International Unit (IU) of enzyme activity is defined as the amount of enzyme that converts what amount of substrate per minute under standard conditions?
a) 1 mol
b) 1 mmol
c) 1 μmol
d) 1 nmol - In spectrophotometry, the formula for calculating the absorbance (A) of a solution is:
a) A = (absorptivity × light path) / concentration
b) A = (absorptivity × concentration) / light path
c) A = absorptivity × light path × concentration
d) A = (light path × concentration) / absorptivity - Given a percent transmittance (%T) of a solution, the absorbance is calculated as:
a) 1 – log(%T)
b) log(%T) + 2
c) 2 × log(%T)
d) 2 – log(%T) - A substance used to detect stray light in a spectrophotometer is a:
a) Mercury vapor lamp
b) Holmium oxide glass
c) Potassium dichromate solution
d) Sharp cutoff filter - The principle of the pO₂ electrode in a blood gas analyzer is:
a) Potentiometry
b) Amperometry
c) Coulometry
d) Conductometry - The purpose of adding sodium fluoride to a blood collection tube for glucose analysis is to:
a) Serve as a coenzyme for hexokinase
b) Precipitate proteins
c) Inhibit glycolysis
d) Prevent reactivity of non-glucose reducing substances - In a method comparison study, if a new method shows a constant systematic error, this will be evident on a scatter plot as a difference in:
a) Slope
b) Intercept
c) Correlation coefficient (r)
d) Standard error of the estimate - A Levey-Jennings chart is used primarily for:
a) Comparing two different analytical methods
b) Monitoring the precision and accuracy of an assay over time
c) Calculating the sensitivity and specificity of a test
d) Establishing reference intervals for a new test - The “1-3s” Westgard rule is considered a violation, indicating possible random error, when:
a) One control value exceeds the mean ± 2SD
b) One control value exceeds the mean ± 3SD
c) Two consecutive controls exceed the mean ± 2SD
d) The difference between two control levels exceeds 4SD - A laboratory implements a new glucose method. To assess the random error (precision) of the method, the laboratory should perform:
a) A comparison of methods study with patient samples.
b) A linearity study using serial dilutions.
c) Replicate testing of a control material over multiple runs.
d) A recovery study by adding analyte to patient samples. - The term “reference range” is typically defined as the interval between which percentiles of a healthy reference population?
a) 1st and 99th
b) 2.5th and 97.5th
c) 5th and 95th
d) 10th and 90th - In the context of quality control, “accuracy” refers to how close a measured value is to the:
a) Average value of repeated measurements
b) True or accepted reference value
c) Value obtained by a reference method
d) Median of the reference range - In a chromatographic method, the term “reverse phase” implies that the mobile phase is:
a) Pumped up the column
b) More polar than the stationary phase
c) Always nonpolar
d) Less polar than the stationary phase - The best course of action for a grossly lipemic serum sample that may interfere with an indirect ISE sodium measurement is to:
a) Dilute the sample with saline and rerun.
b) Use a direct ISE method or ultracentrifuge the sample.
c) Report the result with a comment about lipemic interference.
d) Filter the sample to remove the lipids. - The “Hook effect” in an immunoassay can lead to a falsely low result and is caused by:
a) The presence of heterophilic antibodies
b) An extremely high concentration of analyte
c) Inadequate washing of the reaction vessel
d) Deterioration of the chemiluminescent substrate - To prepare 100 mL of a 15 mg/dL BUN working standard from a 500 mg/dL stock solution, what volume of stock solution is required?
a) 3 mL
b) 5 mL
c) 33 mL
d) 75 mL - A 1:100 dilution of a patient’s serum is made. If 10 μL of serum is used, what is the total volume of the dilution?
a) 1.0 mL
b) 10 mL
c) 100 mL
d) 1000 mL (1 L) - In enzyme kinetics, a Lineweaver-Burk plot is used to determine:
a) The optimal temperature for the reaction
b) The Vmax and Km of the enzyme
c) The activation energy of the reaction
d) The isoelectric point of the enzyme - In competitive enzyme inhibition, the primary effect on kinetic parameters is:
a) Decreased Vmax, unchanged Km
b) Unchanged Vmax, increased Km
c) Decreased Vmax, decreased Km
d) Unchanged Vmax, decreased Km - A serum sample for ammonia determination should be:
a) Incubated at 37°C prior to testing
b) Spun and separated immediately, tested as routine
c) Spun, separated, iced, and tested immediately
d) Stored at room temperature until tested - Which of the following factors is LEAST likely to cause a pre-analytical error in potassium measurement?
a) Prolonged tourniquet application
b) Hemolysis of the sample
c) The patient’s recent dietary intake
d) Delayed separation of serum from cells - A creatinine clearance test requires which of the following for calculation?
a) 24-hour urine volume, urine creatinine, serum creatinine
b) Random urine creatinine and serum creatinine
c) 24-hour urine volume and serum creatinine
d) Urine creatinine and patient’s weight - The Jaffe reaction is a common method for the measurement of:
a) Glucose
b) Total Protein
c) Creatinine
d) Uric Acid - The Biuret method is used for the quantification of:
a) Specific immunoglobulins
b) Total serum protein
c) Serum albumin
d) Urinary microalbumin - In a spectrophotometric assay for Lactate Dehydrogenase (LD), the decrease in absorbance at 340 nm is measured due to the conversion of:
a) NAD to NADH
b) NADH to NAD
c) Lactate to Pyruvate
d) Pyruvate to Lactate (in the forward reaction) - A patient’s serum osmolality is measured at 301 mOsm/kg. The calculated osmolality is 286 mOsm/kg. The elevated osmolal gap suggests the presence of:
a) Unmeasured cations like magnesium
b) Unmeasured osmoles like ethanol or methanol
c) Laboratory calculation error
d) Severe hyponatremia - The primary purpose of a reagent blank in a spectrophotometric assay is to:
a) Check the accuracy of the standard
b) Correct for absorbance due to the reagent itself
c) Monitor the stability of the light source
d) Establish a baseline for the patient sample - A common cause of a falsely decreased sodium value when using an indirect ion-selective electrode is:
a) Hyperglycemia
b) Hyperlipidemia
c) Hemolysis
d) Alkalosis - The term “specificity” of a clinical test refers to its ability to correctly identify:
a) All individuals with the disease (true positives)
b) All individuals without the disease (true negatives)
c) The proportion of true positives in the tested population
d) The accuracy of the method at low concentrations - A laboratory introduces a new test. The “reportable range” is verified by performing a:
a) Linearity study
b) Precision study
c) Reference interval study
d) Method comparison study
📌 How to Use This Practice Set
- Answer each question before checking the key.
- Focus on why the correct answer is right and the others are wrong.
- Use this set as timed practice to simulate the real exam environment.
Answer Key
Answer Key:
- b) Biological catalysts that speed up chemical reactions
- b) Apoenzyme
- b) Coenzyme
- a) Holoenzyme
- b) Decreasing activation energy
- c) Substrate
- b) Active site
- a) pH, temperature, and substrate concentration
- b) Michaelis–Menten equation
- b) Km (Michaelis constant)
- b) Liver
- b) Liver and heart
- b) ALT
- b) Obstructive jaundice and bone disease
- b) Alcoholic liver disease
- b) Pancreatitis
- b) Salivary gland disorder
- b) CK-MB
- b) Prostate cancer
- b) Pesticide poisoning or anesthesia sensitivity
- b) 2.5th and 97.5th
- b) True or accepted reference value
- b) More polar than the stationary phase
- b) Use a direct ISE method or ultracentrifuge the sample.
- b) An extremely high concentration of analyte
- a) 3 mL
- a) 1.0 mL
- b) The Vmax and Km of the enzyme
- b) Unchanged Vmax, increased Km
- c) Spun, separated, iced, and tested immediately
- a) Oxidoreductases
- b) Transferases
- a) Hydrolases
- b) Different forms of an enzyme that catalyze the same reaction
- c) CK-MB
- c) Myoglobin
- b) Rises later but stays elevated longer
- b) Pyruvate and lactate
- c) 4
- b) Myocardial infarction
- c) 1 μmol
- c) A = absorptivity × light path × concentration
- d) 2 – log(%T)
- d) Sharp cutoff filter
- b) Amperometry
- c) Inhibit glycolysis
- b) Intercept
- b) Monitoring the precision and accuracy of an assay over time
- b) One control value exceeds the mean ± 3SD
- c) Replicate testing of a control material over multiple runs.
- c) The patient’s recent dietary intake
- a) 24-hour urine volume, urine creatinine, serum creatinine
- c) Creatinine
- b) Total serum protein
- b) NADH to NAD
- b) Unmeasured osmoles like ethanol or methanol
- b) Correct for absorbance due to the reagent itself
- b) Hyperlipidemia
- b) All individuals without the disease (true negatives)
- a) Linearity study
Top 8 Medical Laboratory Scientist (MLS) Exams:
Top 8 Medical Laboratory Scientist (MLS) Exams that are recognized globally and can help professionals validate their credentials and enhance their career opportunities:
1. ASCP – American Society for Clinical Pathology (USA)
- Exam Name: MLS(ASCP)
- Eligibility: Bachelor’s degree with clinical laboratory experience.
- Global Recognition: High
- Purpose: Certifies Medical Laboratory Scientists in the United States and internationally.
2. AMT – American Medical Technologists (USA)
- Exam Name: MLT(AMT) or MT(AMT)
- Eligibility: Academic and/or work experience in medical laboratory technology.
- Global Recognition: Moderate
- Purpose: Credentialing for medical technologists and technicians.
3. AIMS – Australian Institute of Medical and Clinical Scientists
- Exam Name: AIMS Certification Exam
- Eligibility: Assessment of qualifications and work experience.
- Recognition: Required for practice in Australia.
- Purpose: Certification and registration in Australia.
4. CSMLS – Canadian Society for Medical Laboratory Science
- Exam Name: CSMLS General or Subject-specific Exams
- Eligibility: Graduation from a CSMLS-accredited program or equivalent.
- Recognition: Canada
- Purpose: Entry-to-practice certification in Canada.
5. IBMS – Institute of Biomedical Science (UK)
- Exam Name: Registration and Specialist Portfolio Assessment
- Eligibility: Accredited degree and lab experience.
- Recognition: UK and some Commonwealth countries.
- Purpose: Biomedical Scientist registration with the HCPC (UK).
6. HAAD / DOH – Department of Health, Abu Dhabi (UAE)
- Exam Name: DOH/HAAD License Exam
- Eligibility: Degree in medical laboratory science and experience.
- Recognition: UAE (Abu Dhabi)
- Purpose: Licensure for medical laboratory practice in Abu Dhabi.
7. DHA – Dubai Health Authority (UAE)
- Exam Name: DHA License Exam for Medical Laboratory Technologists
- Eligibility: Relevant degree and experience.
- Recognition: Dubai, UAE
- Purpose: Professional license for clinical laboratory practice in Dubai.
8. MOH – Ministry of Health (Gulf Countries like UAE, Saudi Arabia, Kuwait)
- Exam Name: MOH License Exam
- Eligibility: BSc/Diploma in Medical Laboratory + experience.
- Recognition: Varies by country.
- Purpose: Required for practicing in public and private sector labs.
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#ASCPMLS #MLSexam #LabTech #MedicalLaboratory #BOCexam #FreePracticeQuestions #QualityControl #LaboratorySafety
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