Medical Laboratory Technician Exam Medical Laboratory Technician Clinical Chemistry Procedures 1 — Questions and Answers
Question 1: Which colorimetric method is the standard clinical laboratory procedure for measuring total protein in serum, based on the reaction of peptide bonds with copper ions in alkaline solution?
- Biuret method (Correct answer)
- Bradford assay
- Lowry method
- BCA (bicinchoninic acid) assay
Correct answer: Biuret method
The biuret method is the standard clinical chemistry procedure for total serum protein. Copper(II) ions in alkaline solution form a violet complex with peptide bonds (two or more), producing a color proportional to protein concentration measured at 540 nm.
Question 2: The van den Bergh reaction used in clinical chemistry laboratories distinguishes between which two fractions of bilirubin?
- Direct (conjugated) and indirect (unconjugated) bilirubin (Correct answer)
- Alpha-bilirubin and beta-bilirubin
- Free bilirubin and albumin-bound bilirubin
- Oxidized bilirubin and reduced bilirubin
Correct answer: Direct (conjugated) and indirect (unconjugated) bilirubin
The van den Bergh reaction uses diazonium salts that react directly with conjugated (direct) bilirubin in aqueous solution. Unconjugated (indirect) bilirubin requires addition of an accelerator such as methanol or caffeine to react, allowing differentiation of the two fractions.
Question 3: Ion-selective electrodes (ISE), the most widely used technology for measuring serum electrolytes such as sodium and potassium in clinical chemistry analyzers, operate on which electrochemical principle?
- Potentiometry — measuring the electrical potential difference across an ion-selective membrane (Correct answer)
- Amperometry — measuring current at a fixed applied voltage
- Coulometry — measuring total charge passed during a reaction
- Spectrophotometry — measuring light absorbance at a specific wavelength
Correct answer: Potentiometry — measuring the electrical potential difference across an ion-selective membrane
ISEs are potentiometric devices; they measure the voltage (potential) that develops across a selective membrane permeable only to the target ion. This potential is proportional to the logarithm of ion activity per the Nernst equation, allowing accurate electrolyte quantification.
Question 4: Hemoglobin A1c (HbA1c) is used in clinical chemistry to assess long-term glycemic control because it reflects average blood glucose over approximately what time period?
- 2 to 3 months (Correct answer)
- 1 to 2 weeks
- 6 to 12 months
- 24 to 48 hours
Correct answer: 2 to 3 months
HbA1c results from non-enzymatic glycation of the beta-chain N-terminal valine of hemoglobin. Because red blood cells survive approximately 120 days, HbA1c reflects the mean blood glucose concentration over the preceding 2–3 months, making it the standard marker for long-term glycemic monitoring.
Question 5: In the uricase (enzymatic) method for measuring uric acid in clinical chemistry, what is the direct product detected to quantify uric acid concentration?
- Hydrogen peroxide, which reacts with a chromogen via peroxidase to produce a colored product (Correct answer)
- Carbon dioxide released during uric acid oxidation
- Allantoin measured directly by spectrophotometry at 293 nm
- Ammonia produced from nitrogen-containing ring cleavage
Correct answer: Hydrogen peroxide, which reacts with a chromogen via peroxidase to produce a colored product
Uricase oxidizes uric acid to allantoin and hydrogen peroxide. The H2O2 produced then reacts with a chromogenic oxygen acceptor in the presence of peroxidase (Trinder reaction) to generate a colored compound measured photometrically, providing a specific and sensitive assay.
Question 6: When applying the albumin-adjusted calcium formula in clinical chemistry to correct total calcium for hypoalbuminemia, how much is added to the measured total calcium for each 1 g/dL that serum albumin falls below 4 g/dL?
- 0.8 mg/dL (Correct answer)
- 0.4 mg/dL
- 1.2 mg/dL
- 2.0 mg/dL
Correct answer: 0.8 mg/dL
Approximately 40–45% of serum calcium is protein-bound, primarily to albumin. The standard correction formula adds 0.8 mg/dL to total calcium for every 1 g/dL decrease in albumin below the reference value of 4 g/dL, estimating what total calcium would be under normal albumin conditions.
Medical Laboratory Technician Exam Medical Laboratory Technician Clinical Chemistry Procedures 1
Which colorimetric method is the standard clinical laboratory procedure for measuring total protein in serum, based on the reaction of peptide bonds with copper ions in alkaline solution?