CLS Diagnostic Methods & Technologies 5 — Questions and Answers
Question 1: In flow cytometry, side scatter (SSC) mainly reflects which cellular property?
- Cell size
- DNA content
- Internal complexity or granularity (Correct answer)
- Surface antigen density
Correct answer: Internal complexity or granularity
Side scatter is light deflected at about 90° by internal structures, so granulocytes show high SSC.
Question 2: In an impedance (Coulter principle) cell counter, the height of each voltage pulse is proportional to which property?
- Cell volume (Correct answer)
- Cell granularity
- Nuclear lobulation
- Hemoglobin content
Correct answer: Cell volume
A cell passing through the aperture displaces conductive fluid, and the size of the resistance change matches the cell's volume.
Question 3: Which CD marker is enumerated by flow cytometry to assess hematopoietic progenitor cell yield before stem cell transplant?
- CD3
- CD34 (Correct answer)
- CD19
- CD41
Correct answer: CD34
CD34 is the standard marker for hematopoietic stem and progenitor cells, usually counted with the ISHAGE gating protocol.
Question 4: Which technology lets newborn screening labs measure amino acids and acylcarnitines together from a single dried blood spot?
- Atomic absorption spectrophotometry
- Bacterial inhibition (Guthrie) assay
- Gas chromatography with flame ionization
- Tandem mass spectrometry (MS/MS) (Correct answer)
Correct answer: Tandem mass spectrometry (MS/MS)
MS/MS can quantify dozens of metabolites in one run, which allows panels for amino acid, fatty acid oxidation, and organic acid disorders.
Question 5: A peritoneal dialysis patient using icodextrin has a falsely elevated point-of-care glucose. Which strip chemistry is most likely responsible?
- Glucose oxidase
- Hexokinase
- Glucose dehydrogenase with PQQ cofactor (Correct answer)
- Glucose dehydrogenase with FAD cofactor
Correct answer: Glucose dehydrogenase with PQQ cofactor
GDH-PQQ is not specific for glucose and also reacts with maltose, which forms when icodextrin is metabolized, so results read falsely high.
Question 6: The Clark electrode in a blood gas analyzer measures pO2 by which principle?
- Amperometry, using the current from oxygen reduction at a platinum cathode (Correct answer)
- Potentiometry, using a pH-sensitive glass membrane
- Conductometry, using changes in solution resistance
- Coulometry, using silver ion generation
Correct answer: Amperometry, using the current from oxygen reduction at a platinum cathode
Oxygen diffuses through a membrane and is reduced at a polarized platinum cathode, and the current produced is proportional to pO2.
Question 7: Which HbA1c method measures all glycated hemoglobin and is least affected by common hemoglobin variants such as HbS or HbC?
- Cation-exchange HPLC
- Boronate affinity chromatography (Correct answer)
- Capillary electrophoresis
- Electrophoresis on cellulose acetate
Correct answer: Boronate affinity chromatography
Boronate binds the cis-diol groups of glycated hemoglobin regardless of charge, so structural variants interfere very little.