AACC AACC Instrumentation & Technology 1 — Questions and Answers
Question 1: Which detection principle is used in most automated clinical chemistry analyzers to measure the concentration of an analyte based on light absorption?
- Fluorometry
- Spectrophotometry (Correct answer)
- Nephelometry
- Electrochemiluminescence
Correct answer: Spectrophotometry
Spectrophotometry measures the amount of light absorbed by a solution at a specific wavelength, which is proportional to the analyte concentration per Beer-Lambert's law.
Question 2: In immunoassay analyzers, what does the term 'hook effect' (or 'high-dose hook effect') refer to?
- A mechanical failure in the probe arm
- A falsely low result caused by an extremely high concentration of analyte saturating both capture and detection antibodies (Correct answer)
- A cross-reactivity between two structurally similar analytes
- An instrument error during pipetting of calibrators
Correct answer: A falsely low result caused by an extremely high concentration of analyte saturating both capture and detection antibodies
The hook effect occurs when excess antigen saturates the antibodies in a sandwich immunoassay, resulting in a paradoxically low signal and a falsely low analyte result.
Question 3: What is the purpose of a daily linearity check on a clinical chemistry analyzer?
- To verify that the analyzer can accurately measure analyte concentrations across its full reportable range (Correct answer)
- To test the analyzer's pipetting speed
- To confirm reagent lot compatibility
- To assess analyzer downtime frequency
Correct answer: To verify that the analyzer can accurately measure analyte concentrations across its full reportable range
Linearity checks confirm that the analyzer produces proportionally accurate results across the entire clinically reportable measurement range.
Question 4: Which type of electrode is most commonly used in blood gas analyzers to measure pH?
- Clark electrode
- Severinghaus electrode
- Glass pH electrode (Correct answer)
- Ion-selective electrode for sodium
Correct answer: Glass pH electrode
A glass pH electrode measures hydrogen ion activity by detecting the potential difference across a pH-sensitive glass membrane in blood gas analyzers.
Question 5: In mass spectrometry-based clinical assays (LC-MS/MS), what is the role of the internal standard?
- To calibrate the ion source voltage
- To correct for variations in sample preparation, ionization efficiency, and instrument response (Correct answer)
- To identify the molecular formula of unknown compounds
- To measure total protein in the sample
Correct answer: To correct for variations in sample preparation, ionization efficiency, and instrument response
An internal standard, typically a stable isotope-labeled analog of the analyte, corrects for matrix effects and procedural variability, improving quantitative accuracy.
Question 6: What does the term 'carry-over' mean in the context of automated analyzer performance?
- Transferring patient results to the electronic health record
- Contamination of a sample by residual analyte from a previously analyzed high-concentration sample (Correct answer)
- A repeat analysis triggered by a delta check flag
- Moving samples between different analyzer modules
Correct answer: Contamination of a sample by residual analyte from a previously analyzed high-concentration sample
Carry-over occurs when residual analyte from a high-concentration specimen contaminates the subsequent specimen, potentially causing falsely elevated results.
AACC AACC Instrumentation & Technology 1
Which detection principle is used in most automated clinical chemistry analyzers to measure the concentration of an analyte based on light absorption?