CBET Laboratory and In-Vitro Diagnostic Equipment

Question 1

A hematology analyzer using the Coulter principle counts and sizes blood cells by measuring changes in what physical property as cells pass through an aperture?

Accepted Answer

Electrical impedance

Answer

The Coulter principle (electrical impedance method) works by suspending cells in a conductive electrolyte and passing them through a small aperture. Each cell displaces electrolyte, momentarily increasing resistance. The magnitude of the impedance change corresponds to cell volume, while the frequency of pulses equals cell count.

Question 2

A blood gas analyzer's pO₂ electrode consistently reads 10–15% lower than expected across all QC levels. After confirming the sample path is clear, what is the most likely cause?

Accepted Answer

A fouled or expired Clark electrode membrane

Answer

The Clark polarographic electrode measures oxygen via a gas-permeable membrane. As the membrane ages or becomes protein-fouled, it restricts O₂ diffusion to the cathode, causing consistently low pO₂ readings across all control levels. Air bubbles typically cause falsely HIGH readings and affect only individual samples, not all QC levels.

Question 3

During PM on a clinical centrifuge, a BMET notices excessive vibration during a spin cycle. What should be checked FIRST?

Accepted Answer

Rotor balance and proper symmetrical tube loading

Answer

Vibration in a centrifuge is most commonly caused by imbalanced loads — mismatched tube weights or asymmetric placement in the rotor. An imbalanced rotor can cause catastrophic rotor failure. Motor brushes cause speed issues, not vibration, and the speed control and timer are not mechanical vibration sources.

Question 4

Which regulatory standard specifically mandates that clinical laboratories run quality control specimens at defined intervals before reporting patient results?

Accepted Answer

CLIA '88 (Clinical Laboratory Improvement Amendments)

Answer

CLIA '88 (Clinical Laboratory Improvement Amendments of 1988) sets federal standards for all U.S. clinical laboratory testing, including requirements to run calibrators and QC at minimum defined frequencies before reporting patient results. ISO 9001 is a generic quality standard, 510(k) governs device clearance, and NFPA 99 covers utilities and medical gases.

Question 5

A spectrophotometer used for hemoglobin measurement is checked and found to have a wavelength accuracy error of ±5 nm at 415 nm. Why is this clinically significant?

Accepted Answer

415 nm is the Soret band of hemoglobin, where absorbance changes sharply with wavelength, causing large measurement errors

Answer

Hemoglobin's Soret absorption band at ~415 nm is extremely narrow and steep. Even a small wavelength shift (±5 nm) moves the measurement off the peak into a region of dramatically different absorbance, producing significant inaccuracy. This is why wavelength accuracy is a critical PM parameter for spectrophotometers used in clinical labs.

CBET - Certified Biomedical Equipment Technician Practice Test

CBET - Certified Biomedical Equipment Technician Practice Test

CBET Laboratory and In-Vitro Diagnostic Equipment